[FFmpeg-devel] [PATCH] avformat/mov: avoid seeking back to 0 on HEVC open GOP files

[llyyr <llyyr.public@gmail.com>]

ab77b878f1 attempted to fix the issue of broken packets being sent to
the decoder by implementing logic that kept attempting to PTS-step
backwards until it reached a valid point, however applying this
heuristic meant that in files that had no valid points (such as HEVC
videos shot on iPhones), we'd seek back to sample 0 on every seek
attempt. This meant that files that were previously seekable, albeit
with some skipped frames, were not seekable at all now.

Relax this heuristic a bit by giving up on seeking to a valid point if
we've tried a different sample and we still don't have a valid point to
seek to. This may some frames to be skipped on seeking but it's better
than not being able to seek at all in such files.

Fixes: ab77b878f1 ("avformat/mov: fix seeking with HEVC open GOP files")
---
 libavformat/mov.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/libavformat/mov.c b/libavformat/mov.c
index 1996e0028c..60a4d581d9 100644
--- a/libavformat/mov.c
+++ b/libavformat/mov.c
@@ -9108,7 +9108,7 @@ static int mov_seek_stream(AVFormatContext *s, AVStream *st, int64_t timestamp,
 {
     MOVStreamContext *sc = st->priv_data;
     FFStream *const sti = ffstream(st);
-    int sample, time_sample, ret;
+    int sample, time_sample, ret, next_ts, requested_sample;
     unsigned int i;
 
     // Here we consider timestamp to be PTS, hence try to offset it so that we
@@ -9129,7 +9129,17 @@ static int mov_seek_stream(AVFormatContext *s, AVStream *st, int64_t timestamp,
 
         if (!sample || can_seek_to_key_sample(st, sample, timestamp))
             break;
-        timestamp -= FFMAX(sc->min_sample_duration, 1);
+
+        next_ts = timestamp - FFMAX(sc->min_sample_duration, 1);
+        requested_sample = av_index_search_timestamp(st, next_ts, flags);
+
+        // If we can't seek to the next pts either and it's a different sample,
+        // give up trying to find a good pts to seek to, otherwise we'll end up
+        // seeking back to sample 0 on every seek.
+        if (!can_seek_to_key_sample(st, requested_sample, next_ts) && sample != requested_sample)
+            break;
+
+        timestamp = next_ts;
     }
 
     mov_current_sample_set(sc, sample);
-- 
2.42.0

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