Re: [FFmpeg-devel] [PATCH 1/2] libavformat: Improve ff_configure_buffers_for_index for excessive deltas

[Marton Balint <cus@passwd.hu>]

On Tue, 21 Mar 2023, Martin Storsjö wrote:

> Previously, the ff_configure_buffers_for_index function had
> upper sanity limits of 16 MB (1<<24) for buffer_size and
> 8 MB (1<<23) for short_seek_threshold.
>
> However, if the index analysis showed a need for even larger
> buffer sizes (for a really badly interleaved file), over the
> sanity limits, we previously didn't increase the buffer sizes
> at all.
>
> Instead, if the file shows a need for really large buffers and
> short_seek_threshold, just set them to the maximum sanity limit;
> while it might not be enough for all cases in the file, it might
> be enough for most of it.
>
> This can happen e.g. with a mov file with some tracks containing
> some samples that belong in the start of the file, at the end of
> the mdat, while the rest of the file is mostly reasonably interleaved;
> previously those samples caused the maximum pos_delta to skyrocket,
> skipping any buffer size enlargement.
>
> Signed-off-by: Martin Storsjö <martin@martin.st>
> ---
> libavformat/seek.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/libavformat/seek.c b/libavformat/seek.c
> index a236e285c0..818549dfef 100644
> --- a/libavformat/seek.c
> +++ b/libavformat/seek.c
> @@ -220,7 +220,8 @@ void ff_configure_buffers_for_index(AVFormatContext *s, int64_t time_tolerance)
>     pos_delta *= 2;
>     ctx = ffiocontext(s->pb);
>     /* XXX This could be adjusted depending on protocol*/
> -    if (s->pb->buffer_size < pos_delta && pos_delta < (1<<24)) {
> +    pos_delta = FFMIN(pos_delta, 1<<24);
> +    if (s->pb->buffer_size < pos_delta) {
>         av_log(s, AV_LOG_VERBOSE, "Reconfiguring buffers to size %"PRId64"\n", pos_delta);
>
>         /* realloc the buffer and the original data will be retained */
> @@ -232,9 +233,8 @@ void ff_configure_buffers_for_index(AVFormatContext *s, int64_t time_tolerance)
>         ctx->short_seek_threshold = FFMAX(ctx->short_seek_threshold, pos_delta/2);
>     }
> 
> -    if (skip < (1<<23)) {
> -        ctx->short_seek_threshold = FFMAX(ctx->short_seek_threshold, skip);
> -    }
> +    skip = FFMIN(skip, 1<<23);
> +    ctx->short_seek_threshold = FFMAX(ctx->short_seek_threshold, skip);
> }
> 
> int av_index_search_timestamp(AVStream *st, int64_t wanted_timestamp, int flags)
> -- 
> 2.37.1 (Apple Git-137.1)

LGTM, thanks.

Marton
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