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

[Philip Langdale via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

On Wed, 15 May 2024 01:36:43 +0530
llyyr.public@gmail.com wrote:

> From: 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") Fixes: #10585
> ---
>  libavformat/mov.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index b3fa748f27e8..6174a04c3169 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -10133,7 +10133,7 @@ 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 @@ -10154,7 +10154,17 @@ 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've reached a different sample trying to find a good
> pts to
> +        // seek to, give up searching because 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);

LGTM.

I know it's been a _long time_ since you first sent this; I'll push next
week if there aren't any other comments.

--phil
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