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

[James Almer]

On 10/1/2019 3:11 PM, 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

That patch was already NAKed, and a fixed version sent in replacement.