[FFmpeg-devel] [PATCH 2/9] avformat/aviobuf: check if requested seekback buffer is already read

[Andriy Gelman]

Hi Marton,

On Tue, 29. Sep 23:10, Marton Balint wrote:
> Existing code did not check if the requested seekback buffer is
> already read entirely. In this case, nothing has to be done to guarantee
> seekback.
> 
> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  libavformat/aviobuf.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
> index 9675425349..d94be478ac 100644
> --- a/libavformat/aviobuf.c
> +++ b/libavformat/aviobuf.c
> @@ -999,6 +999,9 @@ 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;
>  
> +    if (buf_size <= s->buf_end - s->buf_ptr)
> +        return 0;
> +
>      buf_size += s->buf_ptr - s->buffer + max_buffer_size;
>  
>      if (buf_size < filled || s->seekable || !s->read_packet)

I was testing this set, and saw commit 53c25ee0736. It discards buffered data by
resetting s->{buf_ptr,buf_end} when we need to read more data. 

Maybe I missed something, but wouldn't this mean that seekback no longer works if
fill_buffer() is called in avio_read_partial().. so defeating the purpose of
ffio_ensure_seekback()?

Thanks,
-- 
Andriy