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

[Calvin Walton]

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);
     }
 
-- 
2.21.0