[FFmpeg-devel] [PATCH] avformat/aviobuf: fix broken logic in ffio_ensure_seekback()

[Marton Balint]

On Wed, 16 Sep 2020, Paul B Mahol wrote:

> This removes big CPU overhead for demuxing chained ogg streams.
>
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
> libavformat/aviobuf.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
> index a77517d712..9dfef2377e 100644
> --- a/libavformat/aviobuf.c
> +++ b/libavformat/aviobuf.c
> @@ -999,10 +999,10 @@ int ffio_ensure_seekback(AVIOContext *s, int64_t buf_size)
>     int filled = s->buf_end - s->buffer;
>     ptrdiff_t checksum_ptr_offset = s->checksum_ptr ? s->checksum_ptr - s->buffer : -1;
> 
> -    buf_size += s->buf_ptr - s->buffer + max_buffer_size;
> -
>     if (buf_size < filled || s->seekable || !s->read_packet)

This does not seem right, the amount of to-be-read data in 
the buffer is (buf_end - buf_ptr), so that is the amount that is seekable 
backwards, not (buf_end - buffer = filled).

Regards,
Marton

>         return 0;
> +    buf_size += s->buf_end - s->buf_ptr + max_buffer_size;
> +
>     av_assert0(!s->write_flag);
>
>     buffer = av_malloc(buf_size);
> -- 
> 2.17.1
>
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