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.

1 files changed, 1 insertions, 0 deletions

diff --git a/libavcodec/nvdec.c b/libavcodec/nvdec.c
index d5cf1058cb..efcd47a7f7 100644
--- a/libavcodec/nvdec.c
+++ b/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;