FFmpeg/libavfilter/avfilter.h

/*
 * filter layer
 * Copyright (c) 2007 Bobby Bingham
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#ifndef AVFILTER_AVFILTER_H
#define AVFILTER_AVFILTER_H

/**
 * @file
 * @ingroup lavfi
 * Main libavfilter public API header
 */

/**
 * @defgroup lavfi Libavfilter - graph-based frame editing library
 * @{
 */

#include <stddef.h>

#include "libavutil/attributes.h"
#include "libavutil/avutil.h"
#include "libavutil/dict.h"
#include "libavutil/frame.h"
#include "libavutil/log.h"
#include "libavutil/samplefmt.h"
#include "libavutil/pixfmt.h"
#include "libavutil/rational.h"

#include "libavfilter/version.h"

/**
 * Return the LIBAVFILTER_VERSION_INT constant.
 */
unsigned avfilter_version(void);

/**
 * Return the libavfilter build-time configuration.
 */
const char *avfilter_configuration(void);

/**
 * Return the libavfilter license.
 */
const char *avfilter_license(void);

typedef struct AVFilterContext AVFilterContext;
typedef struct AVFilterLink    AVFilterLink;
typedef struct AVFilterPad     AVFilterPad;
typedef struct AVFilterFormats AVFilterFormats;

#if FF_API_AVFILTERBUFFER
/**
 * A reference-counted buffer data type used by the filter system. Filters
 * should not store pointers to this structure directly, but instead use the
 * AVFilterBufferRef structure below.
 */
typedef struct AVFilterBuffer {
    uint8_t *data[8];           ///< buffer data for each plane/channel

    /**
     * pointers to the data planes/channels.
     *
     * For video, this should simply point to data[].
     *
     * For planar audio, each channel has a separate data pointer, and
     * linesize[0] contains the size of each channel buffer.
     * For packed audio, there is just one data pointer, and linesize[0]
     * contains the total size of the buffer for all channels.
     *
     * Note: Both data and extended_data will always be set, but for planar
     * audio with more channels that can fit in data, extended_data must be used
     * in order to access all channels.
     */
    uint8_t **extended_data;
    int linesize[8];            ///< number of bytes per line

    /** private data to be used by a custom free function */
    void *priv;
    /**
     * A pointer to the function to deallocate this buffer if the default
     * function is not sufficient. This could, for example, add the memory
     * back into a memory pool to be reused later without the overhead of
     * reallocating it from scratch.
     */
    void (*free)(struct AVFilterBuffer *buf);

    int format;                 ///< media format
    int w, h;                   ///< width and height of the allocated buffer
    unsigned refcount;          ///< number of references to this buffer
} AVFilterBuffer;

#define AV_PERM_READ     0x01   ///< can read from the buffer
#define AV_PERM_WRITE    0x02   ///< can write to the buffer
#define AV_PERM_PRESERVE 0x04   ///< nobody else can overwrite the buffer
#define AV_PERM_REUSE    0x08   ///< can output the buffer multiple times, with the same contents each time
#define AV_PERM_REUSE2   0x10   ///< can output the buffer multiple times, modified each time
#define AV_PERM_NEG_LINESIZES 0x20  ///< the buffer requested can have negative linesizes
#define AV_PERM_ALIGN    0x40   ///< the buffer must be aligned

#define AVFILTER_ALIGN 16 //not part of ABI

/**
 * Audio specific properties in a reference to an AVFilterBuffer. Since
 * AVFilterBufferRef is common to different media formats, audio specific
 * per reference properties must be separated out.
 */
typedef struct AVFilterBufferRefAudioProps {
    uint64_t channel_layout;    ///< channel layout of audio buffer
    int nb_samples;             ///< number of audio samples per channel
    int sample_rate;            ///< audio buffer sample rate
    int channels;               ///< number of channels (do not access directly)
} AVFilterBufferRefAudioProps;

/**
 * Video specific properties in a reference to an AVFilterBuffer. Since
 * AVFilterBufferRef is common to different media formats, video specific
 * per reference properties must be separated out.
 */
typedef struct AVFilterBufferRefVideoProps {
    int w;                      ///< image width
    int h;                      ///< image height
    AVRational sample_aspect_ratio; ///< sample aspect ratio
    int interlaced;             ///< is frame interlaced
    int top_field_first;        ///< field order
    enum AVPictureType pict_type; ///< picture type of the frame
    int key_frame;              ///< 1 -> keyframe, 0-> not
    int qp_table_linesize;                ///< qp_table stride
    int qp_table_size;            ///< qp_table size
    int8_t *qp_table;             ///< array of Quantization Parameters
} AVFilterBufferRefVideoProps;

/**
 * A reference to an AVFilterBuffer. Since filters can manipulate the origin of
 * a buffer to, for example, crop image without any memcpy, the buffer origin
 * and dimensions are per-reference properties. Linesize is also useful for
 * image flipping, frame to field filters, etc, and so is also per-reference.
 *
 * TODO: add anything necessary for frame reordering
 */
typedef struct AVFilterBufferRef {
    AVFilterBuffer *buf;        ///< the buffer that this is a reference to
    uint8_t *data[8];           ///< picture/audio data for each plane
    /**
     * pointers to the data planes/channels.
     *
     * For video, this should simply point to data[].
     *
     * For planar audio, each channel has a separate data pointer, and
     * linesize[0] contains the size of each channel buffer.
     * For packed audio, there is just one data pointer, and linesize[0]
     * contains the total size of the buffer for all channels.
     *
     * Note: Both data and extended_data will always be set, but for planar
     * audio with more channels that can fit in data, extended_data must be used
     * in order to access all channels.
     */
    uint8_t **extended_data;
    int linesize[8];            ///< number of bytes per line

    AVFilterBufferRefVideoProps *video; ///< video buffer specific properties
    AVFilterBufferRefAudioProps *audio; ///< audio buffer specific properties

    /**
     * presentation timestamp. The time unit may change during
     * filtering, as it is specified in the link and the filter code
     * may need to rescale the PTS accordingly.
     */
    int64_t pts;
    int64_t pos;                ///< byte position in stream, -1 if unknown

    int format;                 ///< media format

    int perms;                  ///< permissions, see the AV_PERM_* flags

    enum AVMediaType type;      ///< media type of buffer data

    AVDictionary *metadata;     ///< dictionary containing metadata key=value tags
} AVFilterBufferRef;

/**
 * Copy properties of src to dst, without copying the actual data
 */
attribute_deprecated
void avfilter_copy_buffer_ref_props(AVFilterBufferRef *dst, AVFilterBufferRef *src);

/**
 * Add a new reference to a buffer.
 *
 * @param ref   an existing reference to the buffer
 * @param pmask a bitmask containing the allowable permissions in the new
 *              reference
 * @return      a new reference to the buffer with the same properties as the
 *              old, excluding any permissions denied by pmask
 */
attribute_deprecated
AVFilterBufferRef *avfilter_ref_buffer(AVFilterBufferRef *ref, int pmask);

/**
 * Remove a reference to a buffer. If this is the last reference to the
 * buffer, the buffer itself is also automatically freed.
 *
 * @param ref reference to the buffer, may be NULL
 *
 * @note it is recommended to use avfilter_unref_bufferp() instead of this
 * function
 */
attribute_deprecated
void avfilter_unref_buffer(AVFilterBufferRef *ref);

/**
 * Remove a reference to a buffer and set the pointer to NULL.
 * If this is the last reference to the buffer, the buffer itself
 * is also automatically freed.
 *
 * @param ref pointer to the buffer reference
 */
attribute_deprecated
void avfilter_unref_bufferp(AVFilterBufferRef **ref);
#endif

/**
 * Get the number of channels of a buffer reference.
 */
attribute_deprecated
int avfilter_ref_get_channels(AVFilterBufferRef *ref);

#if FF_API_AVFILTERPAD_PUBLIC
/**
 * A filter pad used for either input or output.
 *
 * See doc/filter_design.txt for details on how to implement the methods.
 *
 * @warning this struct might be removed from public API.
 * users should call avfilter_pad_get_name() and avfilter_pad_get_type()
 * to access the name and type fields; there should be no need to access
 * any other fields from outside of libavfilter.
 */
struct AVFilterPad {
    /**
     * Pad name. The name is unique among inputs and among outputs, but an
     * input may have the same name as an output. This may be NULL if this
     * pad has no need to ever be referenced by name.
     */
    const char *name;

    /**
     * AVFilterPad type.
     */
    enum AVMediaType type;

    /**
     * Input pads:
     * Minimum required permissions on incoming buffers. Any buffer with
     * insufficient permissions will be automatically copied by the filter
     * system to a new buffer which provides the needed access permissions.
     *
     * Output pads:
     * Guaranteed permissions on outgoing buffers. Any buffer pushed on the
     * link must have at least these permissions; this fact is checked by
     * asserts. It can be used to optimize buffer allocation.
     */
    attribute_deprecated int min_perms;

    /**
     * Input pads:
     * Permissions which are not accepted on incoming buffers. Any buffer
     * which has any of these permissions set will be automatically copied
     * by the filter system to a new buffer which does not have those
     * permissions. This can be used to easily disallow buffers with
     * AV_PERM_REUSE.
     *
     * Output pads:
     * Permissions which are automatically removed on outgoing buffers. It
     * can be used to optimize buffer allocation.
     */
    attribute_deprecated int rej_perms;

    /**
     * @deprecated unused
     */
    int (*start_frame)(AVFilterLink *link, AVFilterBufferRef *picref);

    /**
     * Callback function to get a video buffer. If NULL, the filter system will
     * use ff_default_get_video_buffer().
     *
     * Input video pads only.
     */
    AVFrame *(*get_video_buffer)(AVFilterLink *link, int w, int h);

    /**
     * Callback function to get an audio buffer. If NULL, the filter system will
     * use ff_default_get_audio_buffer().
     *
     * Input audio pads only.
     */
    AVFrame *(*get_audio_buffer)(AVFilterLink *link, int nb_samples);

    /**
     * @deprecated unused
     */
    int (*end_frame)(AVFilterLink *link);

    /**
     * @deprecated unused
     */
    int (*draw_slice)(AVFilterLink *link, int y, int height, int slice_dir);

    /**
     * Filtering callback. This is where a filter receives a frame with
     * audio/video data and should do its processing.
     *
     * Input pads only.
     *
     * @return >= 0 on success, a negative AVERROR on error. This function
     * must ensure that frame is properly unreferenced on error if it
     * hasn't been passed on to another filter.
     */
    int (*filter_frame)(AVFilterLink *link, AVFrame *frame);

    /**
     * Frame poll callback. This returns the number of immediately available
     * samples. It should return a positive value if the next request_frame()
     * is guaranteed to return one frame (with no delay).
     *
     * Defaults to just calling the source poll_frame() method.
     *
     * Output pads only.
     */
    int (*poll_frame)(AVFilterLink *link);

    /**
     * Frame request callback. A call to this should result in at least one
     * frame being output over the given link. This should return zero on
     * success, and another value on error.
     * See ff_request_frame() for the error codes with a specific
     * meaning.
     *
     * Output pads only.
     */
    int (*request_frame)(AVFilterLink *link);

    /**
     * Link configuration callback.
     *
     * For output pads, this should set the following link properties:
     * video: width, height, sample_aspect_ratio, time_base
     * audio: sample_rate.
     *
     * This should NOT set properties such as format, channel_layout, etc which
     * are negotiated between filters by the filter system using the
     * query_formats() callback before this function is called.
     *
     * For input pads, this should check the properties of the link, and update
     * the filter's internal state as necessary.
     *
     * For both input and output pads, this should return zero on success,
     * and another value on error.
     */
    int (*config_props)(AVFilterLink *link);

    /**
     * The filter expects a fifo to be inserted on its input link,
     * typically because it has a delay.
     *
     * input pads only.
     */
    int needs_fifo;

    /**
     * The filter expects writable frames from its input link,
     * duplicating data buffers if needed.
     *
     * input pads only.
     */
    int needs_writable;
};
#endif

/**
 * Get the number of elements in a NULL-terminated array of AVFilterPads (e.g.
 * AVFilter.inputs/outputs).
 */
int avfilter_pad_count(const AVFilterPad *pads);

/**
 * Get the name of an AVFilterPad.
 *
 * @param pads an array of AVFilterPads
 * @param pad_idx index of the pad in the array it; is the caller's
 *                responsibility to ensure the index is valid
 *
 * @return name of the pad_idx'th pad in pads
 */
const char *avfilter_pad_get_name(const AVFilterPad *pads, int pad_idx);

/**
 * Get the type of an AVFilterPad.
 *
 * @param pads an array of AVFilterPads
 * @param pad_idx index of the pad in the array; it is the caller's
 *                responsibility to ensure the index is valid
 *
 * @return type of the pad_idx'th pad in pads
 */
enum AVMediaType avfilter_pad_get_type(const AVFilterPad *pads, int pad_idx);

/**
 * The number of the filter inputs is not determined just by AVFilter.inputs.
 * The filter might add additional inputs during initialization depending on the
 * options supplied to it.
 */
#define AVFILTER_FLAG_DYNAMIC_INPUTS        (1 << 0)
/**
 * The number of the filter outputs is not determined just by AVFilter.outputs.
 * The filter might add additional outputs during initialization depending on
 * the options supplied to it.
 */
#define AVFILTER_FLAG_DYNAMIC_OUTPUTS       (1 << 1)
/**
 * The filter supports multithreading by splitting frames into multiple parts
 * and processing them concurrently.
 */
#define AVFILTER_FLAG_SLICE_THREADS         (1 << 2)
/**
 * Some filters support a generic "enable" expression option that can be used
 * to enable or disable a filter in the timeline. Filters supporting this
 * option have this flag set. When the enable expression is false, the default
 * no-op filter_frame() function is called in place of the filter_frame()
 * callback defined on each input pad, thus the frame is passed unchanged to
 * the next filters.
 */
#define AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC  (1 << 16)
/**
 * Same as AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC, except that the filter will
 * have its filter_frame() callback(s) called as usual even when the enable
 * expression is false. The filter will disable filtering within the
 * filter_frame() callback(s) itself, for example executing code depending on
 * the AVFilterContext->is_disabled value.
 */
#define AVFILTER_FLAG_SUPPORT_TIMELINE_INTERNAL (1 << 17)
/**
 * Handy mask to test whether the filter supports or no the timeline feature
 * (internally or generically).
 */
#define AVFILTER_FLAG_SUPPORT_TIMELINE (AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC | AVFILTER_FLAG_SUPPORT_TIMELINE_INTERNAL)

/**
 * Filter definition. This defines the pads a filter contains, and all the
 * callback functions used to interact with the filter.
 */
typedef struct AVFilter {
    /**
     * Filter name. Must be non-NULL and unique among filters.
     */
    const char *name;

    /**
     * A description of the filter. May be NULL.
     *
     * You should use the NULL_IF_CONFIG_SMALL() macro to define it.
     */
    const char *description;

    /**
     * List of inputs, terminated by a zeroed element.
     *
     * NULL if there are no (static) inputs. Instances of filters with
     * AVFILTER_FLAG_DYNAMIC_INPUTS set may have more inputs than present in
     * this list.
     */
    const AVFilterPad *inputs;
    /**
     * List of outputs, terminated by a zeroed element.
     *
     * NULL if there are no (static) outputs. Instances of filters with
     * AVFILTER_FLAG_DYNAMIC_OUTPUTS set may have more outputs than present in
     * this list.
     */
    const AVFilterPad *outputs;

    /**
     * A class for the private data, used to declare filter private AVOptions.
     * This field is NULL for filters that do not declare any options.
     *
     * If this field is non-NULL, the first member of the filter private data
     * must be a pointer to AVClass, which will be set by libavfilter generic
     * code to this class.
     */
    const AVClass *priv_class;

    /**
     * A combination of AVFILTER_FLAG_*
     */
    int flags;

    /*****************************************************************
     * All fields below this line are not part of the public API. They
     * may not be used outside of libavfilter and can be changed and
     * removed at will.
     * New public fields should be added right above.
     *****************************************************************
     */

    /**
     * Filter initialization function.
     *
     * This callback will be called only once during the filter lifetime, after
     * all the options have been set, but before links between filters are
     * established and format negotiation is done.
     *
     * Basic filter initialization should be done here. Filters with dynamic
     * inputs and/or outputs should create those inputs/outputs here based on
     * provided options. No more changes to this filter's inputs/outputs can be
     * done after this callback.
     *
     * This callback must not assume that the filter links exist or frame
     * parameters are known.
     *
     * @ref AVFilter.uninit "uninit" is guaranteed to be called even if
     * initialization fails, so this callback does not have to clean up on
     * failure.
     *
     * @return 0 on success, a negative AVERROR on failure
     */
    int (*init)(AVFilterContext *ctx);

    /**
     * Should be set instead of @ref AVFilter.init "init" by the filters that
     * want to pass a dictionary of AVOptions to nested contexts that are
     * allocated during init.
     *
     * On return, the options dict should be freed and replaced with one that
     * contains all the options which could not be processed by this filter (or
     * with NULL if all the options were processed).
     *
     * Otherwise the semantics is the same as for @ref AVFilter.init "init".
     */
    int (*init_dict)(AVFilterContext *ctx, AVDictionary **options);

    /**
     * Filter uninitialization function.
     *
     * Called only once right before the filter is freed. Should deallocate any
     * memory held by the filter, release any buffer references, etc. It does
     * not need to deallocate the AVFilterContext.priv memory itself.
     *
     * This callback may be called even if @ref AVFilter.init "init" was not
     * called or failed, so it must be prepared to handle such a situation.
     */
    void (*uninit)(AVFilterContext *ctx);

    /**
     * Query formats supported by the filter on its inputs and outputs.
     *
     * This callback is called after the filter is initialized (so the inputs
     * and outputs are fixed), shortly before the format negotiation. This
     * callback may be called more than once.
     *
     * This callback must set AVFilterLink.out_formats on every input link and
     * AVFilterLink.in_formats on every output link to a list of pixel/sample
     * formats that the filter supports on that link. For audio links, this
     * filter must also set @ref AVFilterLink.in_samplerates "in_samplerates" /
     * @ref AVFilterLink.out_samplerates "out_samplerates" and
     * @ref AVFilterLink.in_channel_layouts "in_channel_layouts" /
     * @ref AVFilterLink.out_channel_layouts "out_channel_layouts" analogously.
     *
     * This callback may be NULL for filters with one input, in which case
     * libavfilter assumes that it supports all input formats and preserves
     * them on output.
     *
     * @return zero on success, a negative value corresponding to an
     * AVERROR code otherwise
     */
    int (*query_formats)(AVFilterContext *);

    int priv_size;      ///< size of private data to allocate for the filter

    /**
     * Used by the filter registration system. Must not be touched by any other
     * code.
     */
    struct AVFilter *next;

    /**
     * Make the filter instance process a command.
     *
     * @param cmd    the command to process, for handling simplicity all commands must be alphanumeric only
     * @param arg    the argument for the command
     * @param res    a buffer with size res_size where the filter(s) can return a response. This must not change when the command is not supported.
     * @param flags  if AVFILTER_CMD_FLAG_FAST is set and the command would be
     *               time consuming then a filter should treat it like an unsupported command
     *
     * @returns >=0 on success otherwise an error code.
     *          AVERROR(ENOSYS) on unsupported commands
     */
    int (*process_command)(AVFilterContext *, const char *cmd, const char *arg, char *res, int res_len, int flags);

    /**
     * Filter initialization function, alternative to the init()
     * callback. Args contains the user-supplied parameters, opaque is
     * used for providing binary data.
     */
    int (*init_opaque)(AVFilterContext *ctx, void *opaque);
} AVFilter;

/**
 * Process multiple parts of the frame concurrently.
 */
#define AVFILTER_THREAD_SLICE (1 << 0)

typedef struct AVFilterInternal AVFilterInternal;

/** An instance of a filter */
struct AVFilterContext {
    const AVClass *av_class;        ///< needed for av_log() and filters common options

    const AVFilter *filter;         ///< the AVFilter of which this is an instance

    char *name;                     ///< name of this filter instance

    AVFilterPad   *input_pads;      ///< array of input pads
    AVFilterLink **inputs;          ///< array of pointers to input links
#if FF_API_FOO_COUNT
    attribute_deprecated unsigned input_count; ///< @deprecated use nb_inputs
#endif
    unsigned    nb_inputs;          ///< number of input pads

    AVFilterPad   *output_pads;     ///< array of output pads
    AVFilterLink **outputs;         ///< array of pointers to output links
#if FF_API_FOO_COUNT
    attribute_deprecated unsigned output_count; ///< @deprecated use nb_outputs
#endif
    unsigned    nb_outputs;         ///< number of output pads

    void *priv;                     ///< private data for use by the filter

    struct AVFilterGraph *graph;    ///< filtergraph this filter belongs to

    /**
     * Type of multithreading being allowed/used. A combination of
     * AVFILTER_THREAD_* flags.
     *
     * May be set by the caller before initializing the filter to forbid some
     * or all kinds of multithreading for this filter. The default is allowing
     * everything.
     *
     * When the filter is initialized, this field is combined using bit AND with
     * AVFilterGraph.thread_type to get the final mask used for determining
     * allowed threading types. I.e. a threading type needs to be set in both
     * to be allowed.
     *
     * After the filter is initialzed, libavfilter sets this field to the
     * threading type that is actually used (0 for no multithreading).
     */
    int thread_type;

    /**
     * An opaque struct for libavfilter internal use.
     */
    AVFilterInternal *internal;

    struct AVFilterCommand *command_queue;

    char *enable_str;               ///< enable expression string
    void *enable;                   ///< parsed expression (AVExpr*)
    double *var_values;             ///< variable values for the enable expression
    int is_disabled;                ///< the enabled state from the last expression evaluation
};

/**
 * A link between two filters. This contains pointers to the source and
 * destination filters between which this link exists, and the indexes of
 * the pads involved. In addition, this link also contains the parameters
 * which have been negotiated and agreed upon between the filter, such as
 * image dimensions, format, etc.
 */
struct AVFilterLink {
    AVFilterContext *src;       ///< source filter
    AVFilterPad *srcpad;        ///< output pad on the source filter

    AVFilterContext *dst;       ///< dest filter
    AVFilterPad *dstpad;        ///< input pad on the dest filter

    enum AVMediaType type;      ///< filter media type

    /* These parameters apply only to video */
    int w;                      ///< agreed upon image width
    int h;                      ///< agreed upon image height
    AVRational sample_aspect_ratio; ///< agreed upon sample aspect ratio
    /* These parameters apply only to audio */
    uint64_t channel_layout;    ///< channel layout of current buffer (see libavutil/channel_layout.h)
    int sample_rate;            ///< samples per second

    int format;                 ///< agreed upon media format

    /**
     * Define the time base used by the PTS of the frames/samples
     * which will pass through this link.
     * During the configuration stage, each filter is supposed to
     * change only the output timebase, while the timebase of the
     * input link is assumed to be an unchangeable property.
     */
    AVRational time_base;

    /*****************************************************************
     * All fields below this line are not part of the public API. They
     * may not be used outside of libavfilter and can be changed and
     * removed at will.
     * New public fields should be added right above.
     *****************************************************************
     */
    /**
     * Lists of formats and channel layouts supported by the input and output
     * filters respectively. These lists are used for negotiating the format
     * to actually be used, which will be loaded into the format and
     * channel_layout members, above, when chosen.
     *
     */
    AVFilterFormats *in_formats;
    AVFilterFormats *out_formats;

    /**
     * Lists of channel layouts and sample rates used for automatic
     * negotiation.
     */
    AVFilterFormats  *in_samplerates;
    AVFilterFormats *out_samplerates;
    struct AVFilterChannelLayouts  *in_channel_layouts;
    struct AVFilterChannelLayouts *out_channel_layouts;

    /**
     * Audio only, the destination filter sets this to a non-zero value to
     * request that buffers with the given number of samples should be sent to
     * it. AVFilterPad.needs_fifo must also be set on the corresponding input
     * pad.
     * Last buffer before EOF will be padded with silence.
     */
    int request_samples;

    /** stage of the initialization of the link properties (dimensions, etc) */
    enum {
        AVLINK_UNINIT = 0,      ///< not started
        AVLINK_STARTINIT,       ///< started, but incomplete
        AVLINK_INIT             ///< complete
    } init_state;

    struct AVFilterPool *pool;

    /**
     * Graph the filter belongs to.
     */
    struct AVFilterGraph *graph;

    /**
     * Current timestamp of the link, as defined by the most recent
     * frame(s), in AV_TIME_BASE units.
     */
    int64_t current_pts;

    /**
     * Index in the age array.
     */
    int age_index;

    /**
     * Frame rate of the stream on the link, or 1/0 if unknown;
     * if left to 0/0, will be automatically be copied from the first input
     * of the source filter if it exists.
     *
     * Sources should set it to the best estimation of the real frame rate.
     * Filters should update it if necessary depending on their function.
     * Sinks can use it to set a default output frame rate.
     * It is similar to the r_frame_rate field in AVStream.
     */
    AVRational frame_rate;

    /**
     * Buffer partially filled with samples to achieve a fixed/minimum size.
     */
    AVFrame *partial_buf;

    /**
     * Size of the partial buffer to allocate.
     * Must be between min_samples and max_samples.
     */
    int partial_buf_size;

    /**
     * Minimum number of samples to filter at once. If filter_frame() is
     * called with fewer samples, it will accumulate them in partial_buf.
     * This field and the related ones must not be changed after filtering
     * has started.
     * If 0, all related fields are ignored.
     */
    int min_samples;

    /**
     * Maximum number of samples to filter at once. If filter_frame() is
     * called with more samples, it will split them.
     */
    int max_samples;

    /**
     * The buffer reference currently being received across the link by the
     * destination filter. This is used internally by the filter system to
     * allow automatic copying of buffers which do not have sufficient
     * permissions for the destination. This should not be accessed directly
     * by the filters.
     */
    AVFilterBufferRef *cur_buf_copy;

    /**
     * True if the link is closed.
     * If set, all attemps of start_frame, filter_frame or request_frame
     * will fail with AVERROR_EOF, and if necessary the reference will be
     * destroyed.
     * If request_frame returns AVERROR_EOF, this flag is set on the
     * corresponding link.
     * It can be set also be set by either the source or the destination
     * filter.
     */
    int closed;

    /**
     * Number of channels.
     */
    int channels;

    /**
     * True if a frame is being requested on the link.
     * Used internally by the framework.
     */
    unsigned frame_requested;

    /**
     * Link processing flags.
     */
    unsigned flags;

    /**
     * Number of past frames sent through the link.
     */
    int64_t frame_count;
};

/**
 * Link two filters together.
 *
 * @param src    the source filter
 * @param srcpad index of the output pad on the source filter
 * @param dst    the destination filter
 * @param dstpad index of the input pad on the destination filter
 * @return       zero on success
 */
int avfilter_link(AVFilterContext *src, unsigned srcpad,
                  AVFilterContext *dst, unsigned dstpad);

/**
 * Free the link in *link, and set its pointer to NULL.
 */
void avfilter_link_free(AVFilterLink **link);

/**
 * Get the number of channels of a link.
 */
int avfilter_link_get_channels(AVFilterLink *link);

/**
 * Set the closed field of a link.
 */
void avfilter_link_set_closed(AVFilterLink *link, int closed);

/**
 * Negotiate the media format, dimensions, etc of all inputs to a filter.
 *
 * @param filter the filter to negotiate the properties for its inputs
 * @return       zero on successful negotiation
 */
int avfilter_config_links(AVFilterContext *filter);

#if FF_API_AVFILTERBUFFER
/**
 * Create a buffer reference wrapped around an already allocated image
 * buffer.
 *
 * @param data pointers to the planes of the image to reference
 * @param linesize linesizes for the planes of the image to reference
 * @param perms the required access permissions
 * @param w the width of the image specified by the data and linesize arrays
 * @param h the height of the image specified by the data and linesize arrays
 * @param format the pixel format of the image specified by the data and linesize arrays
 */
attribute_deprecated
AVFilterBufferRef *
avfilter_get_video_buffer_ref_from_arrays(uint8_t * const data[4], const int linesize[4], int perms,
                                          int w, int h, enum AVPixelFormat format);

/**
 * Create an audio buffer reference wrapped around an already
 * allocated samples buffer.
 *
 * See avfilter_get_audio_buffer_ref_from_arrays_channels() for a version
 * that can handle unknown channel layouts.
 *
 * @param data           pointers to the samples plane buffers
 * @param linesize       linesize for the samples plane buffers
 * @param perms          the required access permissions
 * @param nb_samples     number of samples per channel
 * @param sample_fmt     the format of each sample in the buffer to allocate
 * @param channel_layout the channel layout of the buffer
 */
attribute_deprecated
AVFilterBufferRef *avfilter_get_audio_buffer_ref_from_arrays(uint8_t **data,
                                                             int linesize,
                                                             int perms,
                                                             int nb_samples,
                                                             enum AVSampleFormat sample_fmt,
                                                             uint64_t channel_layout);
/**
 * Create an audio buffer reference wrapped around an already
 * allocated samples buffer.
 *
 * @param data           pointers to the samples plane buffers
 * @param linesize       linesize for the samples plane buffers
 * @param perms          the required access permissions
 * @param nb_samples     number of samples per channel
 * @param sample_fmt     the format of each sample in the buffer to allocate
 * @param channels       the number of channels of the buffer
 * @param channel_layout the channel layout of the buffer,
 *                       must be either 0 or consistent with channels
 */
attribute_deprecated
AVFilterBufferRef *avfilter_get_audio_buffer_ref_from_arrays_channels(uint8_t **data,
                                                                      int linesize,
                                                                      int perms,
                                                                      int nb_samples,
                                                                      enum AVSampleFormat sample_fmt,
                                                                      int channels,
                                                                      uint64_t channel_layout);

#endif


#define AVFILTER_CMD_FLAG_ONE   1 ///< Stop once a filter understood the command (for target=all for example), fast filters are favored automatically
#define AVFILTER_CMD_FLAG_FAST  2 ///< Only execute command when its fast (like a video out that supports contrast adjustment in hw)

/**
 * Make the filter instance process a command.
 * It is recommended to use avfilter_graph_send_command().
 */
int avfilter_process_command(AVFilterContext *filter, const char *cmd, const char *arg, char *res, int res_len, int flags);

/** Initialize the filter system. Register all builtin filters. */
void avfilter_register_all(void);

#if FF_API_OLD_FILTER_REGISTER
/** Uninitialize the filter system. Unregister all filters. */
attribute_deprecated
void avfilter_uninit(void);
#endif

/**
 * Register a filter. This is only needed if you plan to use
 * avfilter_get_by_name later to lookup the AVFilter structure by name. A
 * filter can still by instantiated with avfilter_graph_alloc_filter even if it
 * is not registered.
 *
 * @param filter the filter to register
 * @return 0 if the registration was successful, a negative value
 * otherwise
 */
int avfilter_register(AVFilter *filter);

/**
 * Get a filter definition matching the given name.
 *
 * @param name the filter name to find
 * @return     the filter definition, if any matching one is registered.
 *             NULL if none found.
 */
#if !FF_API_NOCONST_GET_NAME
const
#endif
AVFilter *avfilter_get_by_name(const char *name);

/**
 * Iterate over all registered filters.
 * @return If prev is non-NULL, next registered filter after prev or NULL if
 * prev is the last filter. If prev is NULL, return the first registered filter.
 */
const AVFilter *avfilter_next(const AVFilter *prev);

#if FF_API_OLD_FILTER_REGISTER
/**
 * If filter is NULL, returns a pointer to the first registered filter pointer,
 * if filter is non-NULL, returns the next pointer after filter.
 * If the returned pointer points to NULL, the last registered filter
 * was already reached.
 * @deprecated use avfilter_next()
 */
attribute_deprecated
AVFilter **av_filter_next(AVFilter **filter);
#endif

#if FF_API_AVFILTER_OPEN
/**
 * Create a filter instance.
 *
 * @param filter_ctx put here a pointer to the created filter context
 * on success, NULL on failure
 * @param filter    the filter to create an instance of
 * @param inst_name Name to give to the new instance. Can be NULL for none.
 * @return >= 0 in case of success, a negative error code otherwise
 * @deprecated use avfilter_graph_alloc_filter() instead
 */
attribute_deprecated
int avfilter_open(AVFilterContext **filter_ctx, AVFilter *filter, const char *inst_name);
#endif


#if FF_API_AVFILTER_INIT_FILTER
/**
 * Initialize a filter.
 *
 * @param filter the filter to initialize
 * @param args   A string of parameters to use when initializing the filter.
 *               The format and meaning of this string varies by filter.
 * @param opaque Any extra non-string data needed by the filter. The meaning
 *               of this parameter varies by filter.
 * @return       zero on success
 */
attribute_deprecated
int avfilter_init_filter(AVFilterContext *filter, const char *args, void *opaque);
#endif

/**
 * Initialize a filter with the supplied parameters.
 *
 * @param ctx  uninitialized filter context to initialize
 * @param args Options to initialize the filter with. This must be a
 *             ':'-separated list of options in the 'key=value' form.
 *             May be NULL if the options have been set directly using the
 *             AVOptions API or there are no options that need to be set.
 * @return 0 on success, a negative AVERROR on failure
 */
int avfilter_init_str(AVFilterContext *ctx, const char *args);

/**
 * Initialize a filter with the supplied dictionary of options.
 *
 * @param ctx     uninitialized filter context to initialize
 * @param options An AVDictionary filled with options for this filter. On
 *                return this parameter will be destroyed and replaced with
 *                a dict containing options that were not found. This dictionary
 *                must be freed by the caller.
 *                May be NULL, then this function is equivalent to
 *                avfilter_init_str() with the second parameter set to NULL.
 * @return 0 on success, a negative AVERROR on failure
 *
 * @note This function and avfilter_init_str() do essentially the same thing,
 * the difference is in manner in which the options are passed. It is up to the
 * calling code to choose whichever is more preferable. The two functions also
 * behave differently when some of the provided options are not declared as
 * supported by the filter. In such a case, avfilter_init_str() will fail, but
 * this function will leave those extra options in the options AVDictionary and
 * continue as usual.
 */
int avfilter_init_dict(AVFilterContext *ctx, AVDictionary **options);

/**
 * Free a filter context. This will also remove the filter from its
 * filtergraph's list of filters.
 *
 * @param filter the filter to free
 */
void avfilter_free(AVFilterContext *filter);

/**
 * Insert a filter in the middle of an existing link.
 *
 * @param link the link into which the filter should be inserted
 * @param filt the filter to be inserted
 * @param filt_srcpad_idx the input pad on the filter to connect
 * @param filt_dstpad_idx the output pad on the filter to connect
 * @return     zero on success
 */
int avfilter_insert_filter(AVFilterLink *link, AVFilterContext *filt,
                           unsigned filt_srcpad_idx, unsigned filt_dstpad_idx);

#if FF_API_AVFILTERBUFFER
/**
 * Copy the frame properties of src to dst, without copying the actual
 * image data.
 *
 * @return 0 on success, a negative number on error.
 */
attribute_deprecated
int avfilter_copy_frame_props(AVFilterBufferRef *dst, const AVFrame *src);

/**
 * Copy the frame properties and data pointers of src to dst, without copying
 * the actual data.
 *
 * @return 0 on success, a negative number on error.
 */
attribute_deprecated
int avfilter_copy_buf_props(AVFrame *dst, const AVFilterBufferRef *src);
#endif

/**
 * @return AVClass for AVFilterContext.
 *
 * @see av_opt_find().
 */
const AVClass *avfilter_get_class(void);

typedef struct AVFilterGraphInternal AVFilterGraphInternal;

/**
 * A function pointer passed to the @ref AVFilterGraph.execute callback to be
 * executed multiple times, possibly in parallel.
 *
 * @param ctx the filter context the job belongs to
 * @param arg an opaque parameter passed through from @ref
 *            AVFilterGraph.execute
 * @param jobnr the index of the job being executed
 * @param nb_jobs the total number of jobs
 *
 * @return 0 on success, a negative AVERROR on error
 */
typedef int (avfilter_action_func)(AVFilterContext *ctx, void *arg, int jobnr, int nb_jobs);

/**
 * A function executing multiple jobs, possibly in parallel.
 *
 * @param ctx the filter context to which the jobs belong
 * @param func the function to be called multiple times
 * @param arg the argument to be passed to func
 * @param ret a nb_jobs-sized array to be filled with return values from each
 *            invocation of func
 * @param nb_jobs the number of jobs to execute
 *
 * @return 0 on success, a negative AVERROR on error
 */
typedef int (avfilter_execute_func)(AVFilterContext *ctx, avfilter_action_func *func,
                                    void *arg, int *ret, int nb_jobs);

typedef struct AVFilterGraph {
    const AVClass *av_class;
#if FF_API_FOO_COUNT
    attribute_deprecated
    unsigned filter_count_unused;
#endif
    AVFilterContext **filters;
#if !FF_API_FOO_COUNT
    unsigned nb_filters;
#endif

    char *scale_sws_opts; ///< sws options to use for the auto-inserted scale filters
    char *resample_lavr_opts;   ///< libavresample options to use for the auto-inserted resample filters
#if FF_API_FOO_COUNT
    unsigned nb_filters;
#endif

    /**
     * Type of multithreading allowed for filters in this graph. A combination
     * of AVFILTER_THREAD_* flags.
     *
     * May be set by the caller at any point, the setting will apply to all
     * filters initialized after that. The default is allowing everything.
     *
     * When a filter in this graph is initialized, this field is combined using
     * bit AND with AVFilterContext.thread_type to get the final mask used for
     * determining allowed threading types. I.e. a threading type needs to be
     * set in both to be allowed.
     */
    int thread_type;

    /**
     * Maximum number of threads used by filters in this graph. May be set by
     * the caller before adding any filters to the filtergraph. Zero (the
     * default) means that the number of threads is determined automatically.
     */
    int nb_threads;

    /**
     * Opaque object for libavfilter internal use.
     */
    AVFilterGraphInternal *internal;

    /**
     * Opaque user data. May be set by the caller to an arbitrary value, e.g. to
     * be used from callbacks like @ref AVFilterGraph.execute.
     * Libavfilter will not touch this field in any way.
     */
    void *opaque;

    /**
     * This callback may be set by the caller immediately after allocating the
     * graph and before adding any filters to it, to provide a custom
     * multithreading implementation.
     *
     * If set, filters with slice threading capability will call this callback
     * to execute multiple jobs in parallel.
     *
     * If this field is left unset, libavfilter will use its internal
     * implementation, which may or may not be multithreaded depending on the
     * platform and build options.
     */
    avfilter_execute_func *execute;

    char *aresample_swr_opts; ///< swr options to use for the auto-inserted aresample filters, Access ONLY through AVOptions

    /**
     * Private fields
     *
     * The following fields are for internal use only.
     * Their type, offset, number and semantic can change without notice.
     */

    AVFilterLink **sink_links;
    int sink_links_count;

    unsigned disable_auto_convert;
} AVFilterGraph;

/**
 * Allocate a filter graph.
 */
AVFilterGraph *avfilter_graph_alloc(void);

/**
 * Create a new filter instance in a filter graph.
 *
 * @param graph graph in which the new filter will be used
 * @param filter the filter to create an instance of
 * @param name Name to give to the new instance (will be copied to
 *             AVFilterContext.name). This may be used by the caller to identify
 *             different filters, libavfilter itself assigns no semantics to
 *             this parameter. May be NULL.
 *
 * @return the context of the newly created filter instance (note that it is
 *         also retrievable directly through AVFilterGraph.filters or with
 *         avfilter_graph_get_filter()) on success or NULL or failure.
 */
AVFilterContext *avfilter_graph_alloc_filter(AVFilterGraph *graph,
                                             const AVFilter *filter,
                                             const char *name);

/**
 * Get a filter instance with name name from graph.
 *
 * @return the pointer to the found filter instance or NULL if it
 * cannot be found.
 */
AVFilterContext *avfilter_graph_get_filter(AVFilterGraph *graph, char *name);

#if FF_API_AVFILTER_OPEN
/**
 * Add an existing filter instance to a filter graph.
 *
 * @param graphctx  the filter graph
 * @param filter the filter to be added
 *
 * @deprecated use avfilter_graph_alloc_filter() to allocate a filter in a
 * filter graph
 */
attribute_deprecated
int avfilter_graph_add_filter(AVFilterGraph *graphctx, AVFilterContext *filter);
#endif

/**
 * Create and add a filter instance into an existing graph.
 * The filter instance is created from the filter filt and inited
 * with the parameters args and opaque.
 *
 * In case of success put in *filt_ctx the pointer to the created
 * filter instance, otherwise set *filt_ctx to NULL.
 *
 * @param name the instance name to give to the created filter instance
 * @param graph_ctx the filter graph
 * @return a negative AVERROR error code in case of failure, a non
 * negative value otherwise
 */
int avfilter_graph_create_filter(AVFilterContext **filt_ctx, const AVFilter *filt,
                                 const char *name, const char *args, void *opaque,
                                 AVFilterGraph *graph_ctx);

/**
 * Enable or disable automatic format conversion inside the graph.
 *
 * Note that format conversion can still happen inside explicitly inserted
 * scale and aresample filters.
 *
 * @param flags  any of the AVFILTER_AUTO_CONVERT_* constants
 */
void avfilter_graph_set_auto_convert(AVFilterGraph *graph, unsigned flags);

enum {
    AVFILTER_AUTO_CONVERT_ALL  =  0, /**< all automatic conversions enabled */
    AVFILTER_AUTO_CONVERT_NONE = -1, /**< all automatic conversions disabled */
};

/**
 * Check validity and configure all the links and formats in the graph.
 *
 * @param graphctx the filter graph
 * @param log_ctx context used for logging
 * @return >= 0 in case of success, a negative AVERROR code otherwise
 */
int avfilter_graph_config(AVFilterGraph *graphctx, void *log_ctx);

/**
 * Free a graph, destroy its links, and set *graph to NULL.
 * If *graph is NULL, do nothing.
 */
void avfilter_graph_free(AVFilterGraph **graph);

/**
 * A linked-list of the inputs/outputs of the filter chain.
 *
 * This is mainly useful for avfilter_graph_parse() / avfilter_graph_parse2(),
 * where it is used to communicate open (unlinked) inputs and outputs from and
 * to the caller.
 * This struct specifies, per each not connected pad contained in the graph, the
 * filter context and the pad index required for establishing a link.
 */
typedef struct AVFilterInOut {
    /** unique name for this input/output in the list */
    char *name;

    /** filter context associated to this input/output */
    AVFilterContext *filter_ctx;

    /** index of the filt_ctx pad to use for linking */
    int pad_idx;

    /** next input/input in the list, NULL if this is the last */
    struct AVFilterInOut *next;
} AVFilterInOut;

/**
 * Allocate a single AVFilterInOut entry.
 * Must be freed with avfilter_inout_free().
 * @return allocated AVFilterInOut on success, NULL on failure.
 */
AVFilterInOut *avfilter_inout_alloc(void);

/**
 * Free the supplied list of AVFilterInOut and set *inout to NULL.
 * If *inout is NULL, do nothing.
 */
void avfilter_inout_free(AVFilterInOut **inout);

#if AV_HAVE_INCOMPATIBLE_LIBAV_ABI || !FF_API_OLD_GRAPH_PARSE
/**
 * Add a graph described by a string to a graph.
 *
 * @note The caller must provide the lists of inputs and outputs,
 * which therefore must be known before calling the function.
 *
 * @note The inputs parameter describes inputs of the already existing
 * part of the graph; i.e. from the point of view of the newly created
 * part, they are outputs. Similarly the outputs parameter describes
 * outputs of the already existing filters, which are provided as
 * inputs to the parsed filters.
 *
 * @param graph   the filter graph where to link the parsed grap context
 * @param filters string to be parsed
 * @param inputs  linked list to the inputs of the graph
 * @param outputs linked list to the outputs of the graph
 * @return zero on success, a negative AVERROR code on error
 */
int avfilter_graph_parse(AVFilterGraph *graph, const char *filters,
                         AVFilterInOut *inputs, AVFilterInOut *outputs,
                         void *log_ctx);
#else
/**
 * Add a graph described by a string to a graph.
 *
 * @param graph   the filter graph where to link the parsed graph context
 * @param filters string to be parsed
 * @param inputs  pointer to a linked list to the inputs of the graph, may be NULL.
 *                If non-NULL, *inputs is updated to contain the list of open inputs
 *                after the parsing, should be freed with avfilter_inout_free().
 * @param outputs pointer to a linked list to the outputs of the graph, may be NULL.
 *                If non-NULL, *outputs is updated to contain the list of open outputs
 *                after the parsing, should be freed with avfilter_inout_free().
 * @return non negative on success, a negative AVERROR code on error
 * @deprecated Use avfilter_graph_parse_ptr() instead.
 */
attribute_deprecated
int avfilter_graph_parse(AVFilterGraph *graph, const char *filters,
                         AVFilterInOut **inputs, AVFilterInOut **outputs,
                         void *log_ctx);
#endif

/**
 * Add a graph described by a string to a graph.
 *
 * @param graph   the filter graph where to link the parsed graph context
 * @param filters string to be parsed
 * @param inputs  pointer to a linked list to the inputs of the graph, may be NULL.
 *                If non-NULL, *inputs is updated to contain the list of open inputs
 *                after the parsing, should be freed with avfilter_inout_free().
 * @param outputs pointer to a linked list to the outputs of the graph, may be NULL.
 *                If non-NULL, *outputs is updated to contain the list of open outputs
 *                after the parsing, should be freed with avfilter_inout_free().
 * @return non negative on success, a negative AVERROR code on error
 */
int avfilter_graph_parse_ptr(AVFilterGraph *graph, const char *filters,
                             AVFilterInOut **inputs, AVFilterInOut **outputs,
                             void *log_ctx);

/**
 * Add a graph described by a string to a graph.
 *
 * @param[in]  graph   the filter graph where to link the parsed graph context
 * @param[in]  filters string to be parsed
 * @param[out] inputs  a linked list of all free (unlinked) inputs of the
 *                     parsed graph will be returned here. It is to be freed
 *                     by the caller using avfilter_inout_free().
 * @param[out] outputs a linked list of all free (unlinked) outputs of the
 *                     parsed graph will be returned here. It is to be freed by the
 *                     caller using avfilter_inout_free().
 * @return zero on success, a negative AVERROR code on error
 *
 * @note This function returns the inputs and outputs that are left
 * unlinked after parsing the graph and the caller then deals with
 * them.
 * @note This function makes no reference whatsoever to already
 * existing parts of the graph and the inputs parameter will on return
 * contain inputs of the newly parsed part of the graph.  Analogously
 * the outputs parameter will contain outputs of the newly created
 * filters.
 */
int avfilter_graph_parse2(AVFilterGraph *graph, const char *filters,
                          AVFilterInOut **inputs,
                          AVFilterInOut **outputs);

/**
 * Send a command to one or more filter instances.
 *
 * @param graph  the filter graph
 * @param target the filter(s) to which the command should be sent
 *               "all" sends to all filters
 *               otherwise it can be a filter or filter instance name
 *               which will send the command to all matching filters.
 * @param cmd    the command to send, for handling simplicity all commands must be alphanumeric only
 * @param arg    the argument for the command
 * @param res    a buffer with size res_size where the filter(s) can return a response.
 *
 * @returns >=0 on success otherwise an error code.
 *              AVERROR(ENOSYS) on unsupported commands
 */
int avfilter_graph_send_command(AVFilterGraph *graph, const char *target, const char *cmd, const char *arg, char *res, int res_len, int flags);

/**
 * Queue a command for one or more filter instances.
 *
 * @param graph  the filter graph
 * @param target the filter(s) to which the command should be sent
 *               "all" sends to all filters
 *               otherwise it can be a filter or filter instance name
 *               which will send the command to all matching filters.
 * @param cmd    the command to sent, for handling simplicity all commands must be alphanummeric only
 * @param arg    the argument for the command
 * @param ts     time at which the command should be sent to the filter
 *
 * @note As this executes commands after this function returns, no return code
 *       from the filter is provided, also AVFILTER_CMD_FLAG_ONE is not supported.
 */
int avfilter_graph_queue_command(AVFilterGraph *graph, const char *target, const char *cmd, const char *arg, int flags, double ts);


/**
 * Dump a graph into a human-readable string representation.
 *
 * @param graph    the graph to dump
 * @param options  formatting options; currently ignored
 * @return  a string, or NULL in case of memory allocation failure;
 *          the string must be freed using av_free
 */
char *avfilter_graph_dump(AVFilterGraph *graph, const char *options);

/**
 * Request a frame on the oldest sink link.
 *
 * If the request returns AVERROR_EOF, try the next.
 *
 * Note that this function is not meant to be the sole scheduling mechanism
 * of a filtergraph, only a convenience function to help drain a filtergraph
 * in a balanced way under normal circumstances.
 *
 * Also note that AVERROR_EOF does not mean that frames did not arrive on
 * some of the sinks during the process.
 * When there are multiple sink links, in case the requested link
 * returns an EOF, this may cause a filter to flush pending frames
 * which are sent to another sink link, although unrequested.
 *
 * @return  the return value of ff_request_frame(),
 *          or AVERROR_EOF if all links returned AVERROR_EOF
 */
int avfilter_graph_request_oldest(AVFilterGraph *graph);

/**
 * @}
 */

#endif /* AVFILTER_AVFILTER_H */