avcodec: Implement mpeg4 nvdec hwaccel

This was predictably nightmarish, given how ridiculous mpeg4 is.
I had to stare at the cuvid parser output for a long time to work
out what each field was supposed to be, and even then, I still don't
fully understand some of them. Particularly:

vop_coded: If I'm reading the decoder correctly, this flag will always
           be 1 as the decoder will not pass the hwaccel any frame
           where it is not 1.
divx_flags: There's obviously no documentation on what the possible
            flags are. I simply observed that this is '0' for a
            normal bitstream and '5' for packed b-frames.
gmc_enabled: I had a number of guesses as to what this mapped to.
             I picked the condition I did based on when the cuvid
             parser was setting flag.

Also note that as with the vdpau hwaccel, the decoder needs to
consume the entire frame and not the slice.

Changelog

@@ -13,7 +13,7 @@ version <next>:
 - PCE support for extended channel layouts in the AAC encoder
 - native aptX encoder and decoder
 - Raw aptX muxer and demuxer
-- NVIDIA NVDEC-accelerated H.264, HEVC, MPEG-1/2, VC1 and VP9 hwaccel decoding
+- NVIDIA NVDEC-accelerated H.264, HEVC, MPEG-1/2/4, VC1 and VP9 hwaccel decoding
 - Intel QSV-accelerated overlay filter
 - mcompand audio filter
 - acontrast audio filter

configure

@@ -2735,6 +2735,8 @@ mpeg2_xvmc_hwaccel_select="mpeg2video_decoder"
 mpeg4_cuvid_hwaccel_select="mpeg4_cuvid_decoder"
 mpeg4_mediacodec_hwaccel_deps="mediacodec"
 mpeg4_mmal_hwaccel_deps="mmal"
+mpeg4_nvdec_hwaccel_deps="nvdec"
+mpeg4_nvdec_hwaccel_select="mpeg4_decoder"
 mpeg4_vaapi_hwaccel_deps="vaapi"
 mpeg4_vaapi_hwaccel_select="mpeg4_decoder"
 mpeg4_vdpau_hwaccel_deps="vdpau"

libavcodec/Makefile

@@ -861,6 +861,7 @@ OBJS-$(CONFIG_MPEG2_VAAPI_HWACCEL)        += vaapi_mpeg2.o
 OBJS-$(CONFIG_MPEG2_VDPAU_HWACCEL)        += vdpau_mpeg12.o
 OBJS-$(CONFIG_MPEG2_VIDEOTOOLBOX_HWACCEL) += videotoolbox.o
 OBJS-$(CONFIG_MPEG2_XVMC_HWACCEL)         += mpegvideo_xvmc.o
+OBJS-$(CONFIG_MPEG4_NVDEC_HWACCEL)        += nvdec_mpeg4.o
 OBJS-$(CONFIG_MPEG4_VAAPI_HWACCEL)        += vaapi_mpeg4.o
 OBJS-$(CONFIG_MPEG4_VDPAU_HWACCEL)        += vdpau_mpeg4.o
 OBJS-$(CONFIG_MPEG4_VIDEOTOOLBOX_HWACCEL) += videotoolbox.o

libavcodec/allcodecs.c

@@ -106,6 +106,7 @@ static void register_all(void)
     REGISTER_HWACCEL(MPEG4_CUVID,       mpeg4_cuvid);
     REGISTER_HWACCEL(MPEG4_MEDIACODEC,  mpeg4_mediacodec);
     REGISTER_HWACCEL(MPEG4_MMAL,        mpeg4_mmal);
+    REGISTER_HWACCEL(MPEG4_NVDEC,       mpeg4_nvdec);
     REGISTER_HWACCEL(MPEG4_VAAPI,       mpeg4_vaapi);
     REGISTER_HWACCEL(MPEG4_VDPAU,       mpeg4_vdpau);
     REGISTER_HWACCEL(MPEG4_VIDEOTOOLBOX, mpeg4_videotoolbox);

libavcodec/h263dec.c

@@ -714,6 +714,9 @@ const enum AVPixelFormat ff_h263_hwaccel_pixfmt_list_420[] = {
 #if CONFIG_H263_VAAPI_HWACCEL || CONFIG_MPEG4_VAAPI_HWACCEL
     AV_PIX_FMT_VAAPI,
 #endif
+#if CONFIG_MPEG4_NVDEC_HWACCEL
+    AV_PIX_FMT_CUDA,
+#endif
 #if CONFIG_MPEG4_VDPAU_HWACCEL
     AV_PIX_FMT_VDPAU,
 #endif

libavcodec/nvdec.c

@@ -56,6 +56,7 @@ static int map_avcodec_id(enum AVCodecID id)
     case AV_CODEC_ID_HEVC:       return cudaVideoCodec_HEVC;
     case AV_CODEC_ID_MPEG1VIDEO: return cudaVideoCodec_MPEG1;
     case AV_CODEC_ID_MPEG2VIDEO: return cudaVideoCodec_MPEG2;
+    case AV_CODEC_ID_MPEG4:      return cudaVideoCodec_MPEG4;
     case AV_CODEC_ID_VC1:        return cudaVideoCodec_VC1;
     case AV_CODEC_ID_VP9:        return cudaVideoCodec_VP9;
     case AV_CODEC_ID_WMV3:       return cudaVideoCodec_VC1;

libavcodec/nvdec_mpeg4.c

@@ -0,0 +1,121 @@
+/*
+ * MPEG-4 Part 2 HW decode acceleration through NVDEC
+ *
+ * Copyright (c) 2017 Philip Langdale
+ *
+ * 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 "avcodec.h"
+#include "mpeg4video.h"
+#include "nvdec.h"
+#include "decode.h"
+
+static int nvdec_mpeg4_start_frame(AVCodecContext *avctx, const uint8_t *buffer, uint32_t size)
+{
+    Mpeg4DecContext *m = avctx->priv_data;
+    MpegEncContext *s = &m->m;
+
+    NVDECContext      *ctx = avctx->internal->hwaccel_priv_data;
+    CUVIDPICPARAMS     *pp = &ctx->pic_params;
+    CUVIDMPEG4PICPARAMS *ppc = &pp->CodecSpecific.mpeg4;
+    FrameDecodeData *fdd;
+    NVDECFrame *cf;
+    AVFrame *cur_frame = s->current_picture.f;
+
+    int ret, i;
+
+    ret = ff_nvdec_start_frame(avctx, cur_frame);
+    if (ret < 0)
+        return ret;
+
+    fdd = (FrameDecodeData*)cur_frame->private_ref->data;
+    cf  = (NVDECFrame*)fdd->hwaccel_priv;
+
+    *pp = (CUVIDPICPARAMS) {
+        .PicWidthInMbs     = (cur_frame->width  + 15) / 16,
+        .FrameHeightInMbs  = (cur_frame->height + 15) / 16,
+        .CurrPicIdx        = cf->idx,
+
+        .intra_pic_flag    = s->pict_type == AV_PICTURE_TYPE_I,
+        .ref_pic_flag      = s->pict_type == AV_PICTURE_TYPE_I ||
+                             s->pict_type == AV_PICTURE_TYPE_P ||
+                             s->pict_type == AV_PICTURE_TYPE_S,
+
+        .CodecSpecific.mpeg4 = {
+            .ForwardRefIdx                = ff_nvdec_get_ref_idx(s->last_picture.f),
+            .BackwardRefIdx               = ff_nvdec_get_ref_idx(s->next_picture.f),
+
+            .video_object_layer_width     = s->width,
+            .video_object_layer_height    = s->height,
+            .vop_time_increment_bitcount  = m->time_increment_bits,
+            .top_field_first              = s->top_field_first,
+            .resync_marker_disable        = !m->resync_marker,
+            .quant_type                   = s->mpeg_quant,
+            .quarter_sample               = s->quarter_sample,
+            .short_video_header           = avctx->codec->id == AV_CODEC_ID_H263,
+            .divx_flags                   = s->divx_packed ? 5 : 0,
+
+            .vop_coding_type              = s->pict_type - AV_PICTURE_TYPE_I,
+            .vop_coded                    = 1,
+            .vop_rounding_type            = s->no_rounding,
+            .alternate_vertical_scan_flag = s->alternate_scan,
+            .interlaced                   = !s->progressive_sequence,
+            .vop_fcode_forward            = s->f_code,
+            .vop_fcode_backward           = s->b_code,
+            .trd                          = { s->pp_time, s->pp_field_time >> 1 },
+            .trb                          = { s->pb_time, s->pb_field_time >> 1 },
+
+            .gmc_enabled                  = s->pict_type == AV_PICTURE_TYPE_S &&
+                                            m->vol_sprite_usage == GMC_SPRITE,
+        }
+    };
+
+    for (i = 0; i < 64; ++i) {
+        ppc->QuantMatrixIntra[i] = s->intra_matrix[i];
+        ppc->QuantMatrixInter[i] = s->inter_matrix[i];
+    }
+
+    // We need to pass the full frame buffer and not just the slice
+    return ff_nvdec_simple_decode_slice(avctx, buffer, size);
+}
+
+static int nvdec_mpeg4_decode_slice(AVCodecContext *avctx, const uint8_t *buffer, uint32_t size)
+{
+    return 0;
+}
+
+static int nvdec_mpeg4_frame_params(AVCodecContext *avctx,
+                                  AVBufferRef *hw_frames_ctx)
+{
+    // Each frame can at most have one P and one B reference
+    return ff_nvdec_frame_params(avctx, hw_frames_ctx, 2);
+}
+
+AVHWAccel ff_mpeg4_nvdec_hwaccel = {
+    .name                 = "mpeg4_nvdec",
+    .type                 = AVMEDIA_TYPE_VIDEO,
+    .id                   = AV_CODEC_ID_MPEG4,
+    .pix_fmt              = AV_PIX_FMT_CUDA,
+    .start_frame          = nvdec_mpeg4_start_frame,
+    .end_frame            = ff_nvdec_simple_end_frame,
+    .decode_slice         = nvdec_mpeg4_decode_slice,
+    .frame_params         = nvdec_mpeg4_frame_params,
+    .init                 = ff_nvdec_decode_init,
+    .uninit               = ff_nvdec_decode_uninit,
+    .priv_data_size       = sizeof(NVDECContext),
+};

libavcodec/version.h

@@ -29,7 +29,7 @@
 
 #define LIBAVCODEC_VERSION_MAJOR  58
 #define LIBAVCODEC_VERSION_MINOR   3
-#define LIBAVCODEC_VERSION_MICRO 104
+#define LIBAVCODEC_VERSION_MICRO 105
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
                                                LIBAVCODEC_VERSION_MINOR, \