[FFmpeg-devel] [PATCH 1/1] avformat/mov: fix timecode with counter mode flag set

[mindmark at gmail.com]

From: Mark Reid <mindmark at gmail.com>

The current behaviour ends up squaring the avg_frame_rate if the conter mode flag is set.
This messes up the timecode calculation, and looks to me as a regression that 
seems to have been introduced 428b4aac.

The new behaviour is use the "Number of frames" field for avg_frame_rate from the timecode atom as describe here:
    https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html#//apple_ref/doc/uid/TP40000939-CH205-69831

Number of frames
    An 8-bit integer that contains the number of frames per second for the timecode format. 
    If the time is a counter, this is the number of frames for each counter tick.

Here is a sample mov file with the counter flag set
https://www.dropbox.com/s/5l4fucb9lhq523s/timecode_counter_mode.mov

before the patch ffmpeg will report the timecode as:
00:37:11:97 and warns that the timecode framerate is 576000000/1002001

after patch:
14:50:55:02

---
 libavformat/mov.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 2b90e31170..76c1ceb82a 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -2336,24 +2336,17 @@ static int mov_parse_stsd_data(MOVContext *c, AVIOContext *pb,
             tmcd_ctx->tmcd_flags = val;
             st->avg_frame_rate.num = AV_RB32(st->codecpar->extradata + 8); /* timescale */
             st->avg_frame_rate.den = AV_RB32(st->codecpar->extradata + 12); /* frameDuration */
-#if FF_API_LAVF_AVCTX
-FF_DISABLE_DEPRECATION_WARNINGS
-            st->codec->time_base = av_inv_q(st->avg_frame_rate);
-FF_ENABLE_DEPRECATION_WARNINGS
-#endif
+
             /* adjust for per frame dur in counter mode */
             if (tmcd_ctx->tmcd_flags & 0x0008) {
-                int timescale = AV_RB32(st->codecpar->extradata + 8);
-                int framedur = AV_RB32(st->codecpar->extradata + 12);
-                st->avg_frame_rate.num *= timescale;
-                st->avg_frame_rate.den *= framedur;
+                st->avg_frame_rate.num = st->codecpar->extradata[16] /* fps, frames per counter tick in counter mode */;
+                st->avg_frame_rate.den = 1;
+            }
 #if FF_API_LAVF_AVCTX
 FF_DISABLE_DEPRECATION_WARNINGS
-                st->codec->time_base.den *= timescale;
-                st->codec->time_base.num *= framedur;
+            st->codec->time_base = av_inv_q(st->avg_frame_rate);
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
-            }
             if (size > 30) {
                 uint32_t len = AV_RB32(st->codecpar->extradata + 18); /* name atom length */
                 uint32_t format = AV_RB32(st->codecpar->extradata + 22);
-- 
2.29.2