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

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

On 9/23/23 16:40, llyyr wrote:
> 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);

Pinging this as it seems to have been missed. The patch still applies on 
current master and the issue also still exists.
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