[FFmpeg-cvslog] fftools/ffmpeg_dec: improve detection of lavf-guessed durations

[Anton Khirnov]

ffmpeg | branch: master | Anton Khirnov <anton at khirnov.net> | Fri Jul  5 12:19:35 2024 +0200| [ff55d1cc20780dc90457368cb4ccae2435a878b1] | committer: Anton Khirnov

fftools/ffmpeg_dec: improve detection of lavf-guessed durations

Will be useful in following commit.

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=ff55d1cc20780dc90457368cb4ccae2435a878b1
---

 fftools/ffmpeg_dec.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/fftools/ffmpeg_dec.c b/fftools/ffmpeg_dec.c
index 70de151301..c2bcf784b0 100644
--- a/fftools/ffmpeg_dec.c
+++ b/fftools/ffmpeg_dec.c
@@ -260,6 +260,10 @@ static int64_t video_duration_estimate(const DecoderPriv *dp, const AVFrame *fra
     const int  ts_unreliable = dp->flags & DECODER_FLAG_TS_UNRELIABLE;
     const int      fr_forced = dp->flags & DECODER_FLAG_FRAMERATE_FORCED;
     int64_t codec_duration = 0;
+    // difference between this and last frame's timestamps
+    const int64_t ts_diff =
+        (frame->pts != AV_NOPTS_VALUE && dp->last_frame_pts != AV_NOPTS_VALUE) ?
+        frame->pts - dp->last_frame_pts : -1;
 
     // XXX lavf currently makes up frame durations when they are not provided by
     // the container. As there is no way to reliably distinguish real container
@@ -267,8 +271,13 @@ static int64_t video_duration_estimate(const DecoderPriv *dp, const AVFrame *fra
     // the container has timestamps. Eventually lavf should stop making up
     // durations, then this should be simplified.
 
+    // frame duration is unreliable (typically guessed by lavf) when it is equal
+    // to 1 and the actual duration of the last frame is more than 2x larger
+    const int duration_unreliable = frame->duration == 1 && ts_diff > 2 * frame->duration;
+
     // prefer frame duration for containers with timestamps
-    if (frame->duration > 0 && (!ts_unreliable || fr_forced))
+    if (fr_forced ||
+        (frame->duration > 0 && !ts_unreliable && !duration_unreliable))
         return frame->duration;
 
     if (dp->dec_ctx->framerate.den && dp->dec_ctx->framerate.num) {
@@ -285,9 +294,8 @@ static int64_t video_duration_estimate(const DecoderPriv *dp, const AVFrame *fra
 
     // when timestamps are available, repeat last frame's actual duration
     // (i.e. pts difference between this and last frame)
-    if (frame->pts != AV_NOPTS_VALUE && dp->last_frame_pts != AV_NOPTS_VALUE &&
-        frame->pts > dp->last_frame_pts)
-        return frame->pts - dp->last_frame_pts;
+    if (ts_diff > 0)
+        return ts_diff;
 
     // try frame/codec duration
     if (frame->duration > 0)