apng: Add a basic APNG muxer

Additionally, update some documentation with support for APNG

Signed-off-by: Donny Yang <work@kota.moe>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

Changelog

@@ -12,6 +12,7 @@ version <next>:
 - Detelecine filter
 - Intel QSV-accelerated H.264 encoding
 - MMAL-accelerated H.264 decoding
+- basic APNG encoder and muxer
 
 
 version 2.6:

doc/general.texi

@@ -222,6 +222,7 @@ library:
     @tab Audio format used on the Nintendo Gamecube.
 @item AFC                       @tab   @tab X
     @tab Audio format used on the Nintendo Gamecube.
+@item APNG                      @tab X @tab X
 @item ASF                       @tab X @tab X
 @item AST                       @tab X @tab X
     @tab Audio format used on the Nintendo Wii.
@@ -508,6 +509,7 @@ following image formats are supported:
 @item Alias PIX    @tab X @tab X
     @tab Alias/Wavefront PIX image format
 @item animated GIF @tab X @tab X
+@item APNG         @tab X @tab X
 @item BMP          @tab X @tab X
     @tab Microsoft BMP image
 @item BRender PIX  @tab   @tab X

libavformat/Makefile

@@ -80,6 +80,7 @@ OBJS-$(CONFIG_ANM_DEMUXER)               += anm.o
 OBJS-$(CONFIG_APC_DEMUXER)               += apc.o
 OBJS-$(CONFIG_APE_DEMUXER)               += ape.o apetag.o img2.o
 OBJS-$(CONFIG_APNG_DEMUXER)              += apngdec.o
+OBJS-$(CONFIG_APNG_MUXER)                += apngenc.o
 OBJS-$(CONFIG_AQTITLE_DEMUXER)           += aqtitledec.o subtitles.o
 OBJS-$(CONFIG_ASF_DEMUXER)               += asfdec.o asf.o asfcrypt.o \
                                             avlanguage.o

libavformat/allformats.c

@@ -74,7 +74,7 @@ void av_register_all(void)
     REGISTER_DEMUXER (ANM,              anm);
     REGISTER_DEMUXER (APC,              apc);
     REGISTER_DEMUXER (APE,              ape);
-    REGISTER_DEMUXER (APNG,             apng);
+    REGISTER_MUXDEMUX(APNG,             apng);
     REGISTER_DEMUXER (AQTITLE,          aqtitle);
     REGISTER_MUXDEMUX(ASF,              asf);
     REGISTER_MUXDEMUX(ASS,              ass);

libavformat/apngenc.c

@@ -0,0 +1,271 @@
+/*
+ * APNG muxer
+ * Copyright (c) 2015 Donny Yang
+ *
+ * first version by Donny Yang <work@kota.moe>
+ *
+ * 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
+ */
+
+#include "avformat.h"
+#include "internal.h"
+#include "libavutil/avassert.h"
+#include "libavutil/crc.h"
+#include "libavutil/intreadwrite.h"
+#include "libavutil/log.h"
+#include "libavutil/opt.h"
+#include "libavcodec/png.h"
+#include "libavcodec/apng.h"
+
+typedef struct APNGMuxContext {
+    AVClass *class;
+
+    uint32_t plays;
+    AVRational last_delay;
+
+    uint64_t acTL_offset;
+    uint32_t frame_number;
+
+    AVPacket *prev_packet;
+    AVRational prev_delay;
+
+    int framerate_warned;
+} APNGMuxContext;
+
+static uint8_t *apng_find_chunk(uint32_t tag, uint8_t *buf, size_t length)
+{
+    size_t b;
+    for (b = 0; b < length; b += AV_RB32(buf + b) + 12)
+        if (AV_RB32(&buf[b + 4]) == tag)
+            return &buf[b];
+    return NULL;
+}
+
+static void apng_write_chunk(AVIOContext *io_context, uint32_t tag,
+                             uint8_t *buf, size_t length)
+{
+    const AVCRC *crc_table = av_crc_get_table(AV_CRC_32_IEEE_LE);
+    uint32_t crc = ~0U;
+    uint8_t tagbuf[4];
+
+    av_assert0(crc_table);
+
+    avio_wb32(io_context, length);
+    AV_WB32(tagbuf, tag);
+    crc = av_crc(crc_table, crc, tagbuf, 4);
+    avio_wb32(io_context, tag);
+    if (length > 0) {
+        crc = av_crc(crc_table, crc, buf, length);
+        avio_write(io_context, buf, length);
+    }
+    avio_wb32(io_context, ~crc);
+}
+
+static int apng_write_header(AVFormatContext *format_context)
+{
+    APNGMuxContext *apng = format_context->priv_data;
+
+    if (format_context->nb_streams != 1 ||
+        format_context->streams[0]->codec->codec_type != AVMEDIA_TYPE_VIDEO ||
+        format_context->streams[0]->codec->codec_id   != AV_CODEC_ID_APNG) {
+        av_log(format_context, AV_LOG_ERROR,
+               "APNG muxer supports only a single video APNG stream.\n");
+        return AVERROR(EINVAL);
+    }
+
+    if (apng->last_delay.num > USHRT_MAX || apng->last_delay.den > USHRT_MAX) {
+        av_reduce(&apng->last_delay.num, &apng->last_delay.den,
+                  apng->last_delay.num, apng->last_delay.den, USHRT_MAX);
+        av_log(format_context, AV_LOG_WARNING,
+               "Last frame delay is too precise. Reducing to %d/%d (%f).\n",
+               apng->last_delay.num, apng->last_delay.den, (double)apng->last_delay.num / apng->last_delay.den);
+    }
+
+    avio_wb64(format_context->pb, PNGSIG);
+    // Remaining headers are written when they are copied from the encoder
+
+    return 0;
+}
+
+static void flush_packet(AVFormatContext *format_context, AVPacket *packet)
+{
+    APNGMuxContext *apng = format_context->priv_data;
+    AVIOContext *io_context = format_context->pb;
+    AVStream *codec_stream = format_context->streams[0];
+    AVCodecContext *codec_context = codec_stream->codec;
+
+    av_assert0(apng->prev_packet);
+
+    if (apng->frame_number == 0 && !packet) {
+        uint8_t *existing_acTL_chunk;
+        uint8_t *existing_fcTL_chunk;
+
+        av_log(format_context, AV_LOG_WARNING, "Only a single frame so saving as a normal PNG.\n");
+
+        // Write normal PNG headers without acTL chunk
+        existing_acTL_chunk = apng_find_chunk(MKBETAG('a', 'c', 'T', 'L'), codec_context->extradata, codec_context->extradata_size);
+        if (existing_acTL_chunk) {
+            uint8_t *chunk_after_acTL = existing_acTL_chunk + AV_RB32(existing_acTL_chunk) + 12;
+            avio_write(io_context, codec_context->extradata, existing_acTL_chunk - codec_context->extradata);
+            avio_write(io_context, chunk_after_acTL, codec_context->extradata + codec_context->extradata_size - chunk_after_acTL);
+        } else {
+            avio_write(io_context, codec_context->extradata, codec_context->extradata_size);
+        }
+
+        // Write frame data without fcTL chunk
+        existing_fcTL_chunk = apng_find_chunk(MKBETAG('f', 'c', 'T', 'L'), apng->prev_packet->data, apng->prev_packet->size);
+        if (existing_fcTL_chunk) {
+            uint8_t *chunk_after_fcTL = existing_fcTL_chunk + AV_RB32(existing_fcTL_chunk) + 12;
+            avio_write(io_context, apng->prev_packet->data, existing_fcTL_chunk - apng->prev_packet->data);
+            avio_write(io_context, chunk_after_fcTL, apng->prev_packet->data + apng->prev_packet->size - chunk_after_fcTL);
+        } else {
+            avio_write(io_context, apng->prev_packet->data, apng->prev_packet->size);
+        }
+    } else {
+        uint8_t *existing_fcTL_chunk;
+
+        if (apng->frame_number == 0) {
+            uint8_t *existing_acTL_chunk;
+
+            // Write normal PNG headers
+            avio_write(io_context, codec_context->extradata, codec_context->extradata_size);
+
+            existing_acTL_chunk = apng_find_chunk(MKBETAG('a', 'c', 'T', 'L'), codec_context->extradata, codec_context->extradata_size);
+            if (!existing_acTL_chunk) {
+                uint8_t buf[8];
+                // Write animation control header
+                apng->acTL_offset = avio_tell(io_context);
+                AV_WB32(buf, UINT_MAX); // number of frames (filled in later)
+                AV_WB32(buf + 4, apng->plays);
+                apng_write_chunk(io_context, MKBETAG('a', 'c', 'T', 'L'), buf, 8);
+            }
+        }
+
+        existing_fcTL_chunk = apng_find_chunk(MKBETAG('f', 'c', 'T', 'L'), apng->prev_packet->data, apng->prev_packet->size);
+        if (existing_fcTL_chunk) {
+            AVRational delay;
+
+            existing_fcTL_chunk += 8;
+            delay.num = AV_RB16(existing_fcTL_chunk + 20);
+            delay.den = AV_RB16(existing_fcTL_chunk + 22);
+
+            if (delay.num == 0 && delay.den == 0) {
+                if (packet) {
+                    int64_t delay_num_raw = (packet->dts - apng->prev_packet->dts) * codec_stream->time_base.num;
+                    int64_t delay_den_raw = codec_stream->time_base.den;
+                    if (!av_reduce(&delay.num, &delay.den, delay_num_raw, delay_den_raw, USHRT_MAX) &&
+                        !apng->framerate_warned) {
+                        av_log(format_context, AV_LOG_WARNING,
+                               "Frame rate is too high or specified too precisely. Unable to copy losslessly.\n");
+                        apng->framerate_warned = 1;
+                    }
+                } else if (apng->last_delay.den > 0) {
+                    delay = apng->last_delay;
+                } else {
+                    delay = apng->prev_delay;
+                }
+
+                // Update frame control header with new delay
+                AV_WB16(existing_fcTL_chunk + 20, delay.num);
+                AV_WB16(existing_fcTL_chunk + 22, delay.den);
+                AV_WB32(existing_fcTL_chunk + 26, ~av_crc(av_crc_get_table(AV_CRC_32_IEEE_LE), ~0U, existing_fcTL_chunk - 4, 26 + 4));
+            }
+            apng->prev_delay = delay;
+        }
+
+        // Write frame data
+        avio_write(io_context, apng->prev_packet->data, apng->prev_packet->size);
+    }
+    ++apng->frame_number;
+
+    av_free_packet(apng->prev_packet);
+    if (packet)
+        av_copy_packet(apng->prev_packet, packet);
+}
+
+static int apng_write_packet(AVFormatContext *format_context, AVPacket *packet)
+{
+    APNGMuxContext *apng = format_context->priv_data;
+
+    if (!apng->prev_packet) {
+        apng->prev_packet = av_malloc(sizeof(*apng->prev_packet));
+        if (!apng->prev_packet)
+            return AVERROR(ENOMEM);
+
+        av_copy_packet(apng->prev_packet, packet);
+    } else {
+        flush_packet(format_context, packet);
+    }
+
+    return 0;
+}
+
+static int apng_write_trailer(AVFormatContext *format_context)
+{
+    APNGMuxContext *apng = format_context->priv_data;
+    AVIOContext *io_context = format_context->pb;
+    uint8_t buf[8];
+
+    if (apng->prev_packet) {
+        flush_packet(format_context, NULL);
+        av_freep(&apng->prev_packet);
+    }
+
+    apng_write_chunk(io_context, MKBETAG('I', 'E', 'N', 'D'), NULL, 0);
+
+    if (apng->acTL_offset && io_context->seekable) {
+        avio_seek(io_context, apng->acTL_offset, SEEK_SET);
+
+        AV_WB32(buf, apng->frame_number);
+        AV_WB32(buf + 4, apng->plays);
+        apng_write_chunk(io_context, MKBETAG('a', 'c', 'T', 'L'), buf, 8);
+    }
+
+    return 0;
+}
+
+#define OFFSET(x) offsetof(APNGMuxContext, x)
+#define ENC AV_OPT_FLAG_ENCODING_PARAM
+static const AVOption options[] = {
+    { "plays", "Number of times to play the output: 0 - infinite loop, 1 - no loop", OFFSET(plays),
+      AV_OPT_TYPE_INT, { .i64 = 1 }, 0, UINT_MAX, ENC },
+    { "final_delay", "Force delay after the last frame", OFFSET(last_delay),
+      AV_OPT_TYPE_RATIONAL, { .dbl = 0 }, 0, USHRT_MAX, ENC },
+    { NULL },
+};
+
+static const AVClass apng_muxer_class = {
+    .class_name = "APNG muxer",
+    .item_name  = av_default_item_name,
+    .version    = LIBAVUTIL_VERSION_INT,
+    .option     = options,
+};
+
+AVOutputFormat ff_apng_muxer = {
+    .name           = "apng",
+    .long_name      = NULL_IF_CONFIG_SMALL("Animated Portable Network Graphics"),
+    .mime_type      = "image/png",
+    .extensions     = "png",
+    .priv_data_size = sizeof(APNGMuxContext),
+    .audio_codec    = AV_CODEC_ID_NONE,
+    .video_codec    = AV_CODEC_ID_APNG,
+    .write_header   = apng_write_header,
+    .write_packet   = apng_write_packet,
+    .write_trailer  = apng_write_trailer,
+    .priv_class     = &apng_muxer_class,
+    .flags          = AVFMT_VARIABLE_FPS,
+};