[FFmpeg-devel] [PATCH 1/3] avformat/avio: add resizeable field to AVIOContext

[wm4]

On Tue, 21 Apr 2015 13:22:00 +0200
Michael Niedermayer <michaelni at gmx.at> wrote:

> This indicates that its safe to use av_free/av_malloc on the IO context
> 
> Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> ---
>  libavformat/avio.h    |    7 +++++++
>  libavformat/aviobuf.c |    1 +
>  libavformat/segment.c |    1 +
>  libavformat/wtvdec.c  |    3 ++-
>  4 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/libavformat/avio.h b/libavformat/avio.h
> index 51913e3..73d1645 100644
> --- a/libavformat/avio.h
> +++ b/libavformat/avio.h
> @@ -196,6 +196,13 @@ typedef struct AVIOContext {
>       * This field is internal to libavformat and access from outside is not allowed.
>       */
>      int orig_buffer_size;
> +
> +    /**
> +     * The io buffer can be resized or freed with av_free / av_malloc.
> +     * The user application does not keep a private copy of the buffer pointer
> +     * which would become stale on such reallocation.
> +     */
> +    int resizeable;
>  } AVIOContext;
>  
>  /* unbuffered I/O */
> diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
> index 7de59f1..b32ff9f 100644
> --- a/libavformat/aviobuf.c
> +++ b/libavformat/aviobuf.c
> @@ -793,6 +793,7 @@ int ffio_fdopen(AVIOContext **s, URLContext *h)
>          (*s)->read_seek  = (int64_t (*)(void *, int, int64_t, int))h->prot->url_read_seek;
>      }
>      (*s)->av_class = &ff_avio_class;
> +    (*s)->resizeable = 1;
>      return 0;
>  }
>  
> diff --git a/libavformat/segment.c b/libavformat/segment.c
> index 1162ea2..6504b46 100644
> --- a/libavformat/segment.c
> +++ b/libavformat/segment.c
> @@ -511,6 +511,7 @@ static int open_null_ctx(AVIOContext **ctx)
>          av_free(buf);
>          return AVERROR(ENOMEM);
>      }
> +    (*ctx)->resizeable = 1;
>      return 0;
>  }
>  
> diff --git a/libavformat/wtvdec.c b/libavformat/wtvdec.c
> index e226690..7b5477b 100644
> --- a/libavformat/wtvdec.c
> +++ b/libavformat/wtvdec.c
> @@ -243,7 +243,8 @@ static AVIOContext * wtvfile_open_sector(int first_sector, uint64_t length, int
>          av_freep(&buffer);
>          av_freep(&wf->sectors);
>          av_freep(&wf);
> -    }
> +    } else
> +        pb->resizeable = 1;
>      return pb;
>  }
>  

Looking at it again, ffio_ensure_seekback and ffio_set_buf_size are
functions which resize the buffer (but by allocating a new buffer to
avoid av_realloc incompatibility, as Nicolas pointed out).

So what's the point of this patch?