[FFmpeg-devel] [PATCH] ivfdec/ivfenc: Match behaviour of libvpx and chromium

[Raphaël Zumer]

This is a superset of my patch(es). It should match the behavior of
libvpx more closely, but the validity of the change from duration to
number of frames depends on your interpretation of the reference
implementation, which comments the field as "length".

On Tue, 2019-10-01 at 23:41 +0530, Gyan wrote:
> 
> On 01-10-2019 11:26 PM, Calvin Walton wrote:
> > The ffmpeg code read and wrote a 64bit duration field (in timebase
> > units) in the ivf
> > header, where the libvpx and chromium code instead use a 32bit
> > frame count field, and
> > then 32bits of unused (reserved?) space.
> > 
> > Switch ffmpeg to match the behaviour of libvpx & chromium.
> > 
> > Note that libvpx writes 0 to the frame count field when initially
> > writing the header
> > then seeks back and overwrites it with the real frame count. ffmpeg
> > used to write
> > 0xFFFFFFFF - I've changed the behaviour to match libvpx.
> > 
> > References:
> > https://github.com/webmproject/libvpx/blob/v1.8.1/ivfenc.c#L16
> > Which is called from:
> > https://github.com/webmproject/libvpx/blob/v1.8.1/vpxenc.c#L1191
> > (initial header)
> > https://github.com/webmproject/libvpx/blob/v1.8.1/vpxenc.c#L1209
> > (rewrite with frame count)
> > And the chromium parser:
> > https://chromium.googlesource.com/chromium/src/media/+/1681b9abff73fe0e3d0932aefdab4f039a284d1a/filters/ivf_parser.h
> > ---
> >   libavformat/ivfdec.c |  3 ++-
> >   libavformat/ivfenc.c | 11 ++++-------
> >   2 files changed, 6 insertions(+), 8 deletions(-)
> > 
> > diff --git a/libavformat/ivfdec.c b/libavformat/ivfdec.c
> > index 40ae464b76..2eaa5164ff 100644
> > --- a/libavformat/ivfdec.c
> > +++ b/libavformat/ivfdec.c
> > @@ -53,7 +53,8 @@ static int read_header(AVFormatContext *s)
> >       st->codecpar->height     = avio_rl16(s->pb);
> >       time_base.den         = avio_rl32(s->pb);
> >       time_base.num         = avio_rl32(s->pb);
> > -    st->duration          = avio_rl64(s->pb);
> > +    st->nb_frames         = avio_rl32(s->pb);
> > +    avio_skip(s->pb, 4); // 32 bits unused
> >   
> >       st->need_parsing      = AVSTREAM_PARSE_HEADERS;
> >   
> > diff --git a/libavformat/ivfenc.c b/libavformat/ivfenc.c
> > index adf72117e9..85ca6045ba 100644
> > --- a/libavformat/ivfenc.c
> > +++ b/libavformat/ivfenc.c
> > @@ -22,8 +22,7 @@
> >   #include "libavutil/intreadwrite.h"
> >   
> >   typedef struct IVFEncContext {
> > -    unsigned frame_cnt;
> > -    uint64_t last_pts, sum_delta_pts;
> > +    uint32_t frame_cnt;
> >   } IVFEncContext;
> >   
> >   static int ivf_write_header(AVFormatContext *s)
> > @@ -53,7 +52,8 @@ static int ivf_write_header(AVFormatContext *s)
> >       avio_wl16(pb, par->height);
> >       avio_wl32(pb, s->streams[0]->time_base.den);
> >       avio_wl32(pb, s->streams[0]->time_base.num);
> > -    avio_wl64(pb, 0xFFFFFFFFFFFFFFFFULL);
> > +    avio_wl32(pb, 0); // frame count
> > +    avio_wl32(pb, 0); // unused
> >   
> >       return 0;
> >   }
> > @@ -66,10 +66,7 @@ static int ivf_write_packet(AVFormatContext *s,
> > AVPacket *pkt)
> >       avio_wl32(pb, pkt->size);
> >       avio_wl64(pb, pkt->pts);
> >       avio_write(pb, pkt->data, pkt->size);
> > -    if (ctx->frame_cnt)
> > -        ctx->sum_delta_pts += pkt->pts - ctx->last_pts;
> >       ctx->frame_cnt++;
> > -    ctx->last_pts = pkt->pts;
> >   
> >       return 0;
> >   }
> > @@ -83,7 +80,7 @@ static int ivf_write_trailer(AVFormatContext *s)
> >           size_t end = avio_tell(pb);
> >   
> >           avio_seek(pb, 24, SEEK_SET);
> > -        avio_wl64(pb, ctx->frame_cnt * ctx->sum_delta_pts / (ctx-
> > >frame_cnt - 1));
> > +        avio_wl32(pb, ctx->frame_cnt);
> >           avio_seek(pb, end, SEEK_SET);
> >       }
> 
> See 
> http://www.ffmpeg.org/pipermail/ffmpeg-devel/2019-October/250871.html
> 
> Gyan
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