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/allcodecs.c b/libavcodec/allcodecs.c
index e9df704..85c38c8 100644
--- a/libavcodec/allcodecs.c
+++ b/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);