[FFmpeg-devel] [PATCH 01/54] avformat: Add internal flags for AV(In|Out)putFormat

[James Almer]

On 6/15/2021 8:01 PM, Andreas Rheinhardt wrote:
> Both AVInputFormat and AVOutputFormat currently lack an equivalent to
> AVCodec's caps_internal. E.g. if reading a header fails, each demuxer
> is currently required to clean up manually, which often means to just
> call the demuxer's read_close function. This could (and will) be done
> generically via an equivalent of FF_CODEC_CAP_INIT_CLEANUP.
> 
> Because of the unholy ABI-relationship between libavdevice and
> libavformat adding such a flag is only possible when the ABI is open
> (despite the flag not being part of the public API), such as now.
> Therefore such a flag is also added to AVOutputFormat, despite there
> being no immediate use for it.

Since new "non public" fields can if needed be added at the very end of 
the struct, is this still an issue?
It's adding new public ones which generate issues because they will 
invariably push the offset of all the non public ones down by a few 
bytes, and thus break lavd devices.

> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
> ---
>   libavformat/avformat.h | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> index cd7b0d941c..81d2ac38d0 100644
> --- a/libavformat/avformat.h
> +++ b/libavformat/avformat.h
> @@ -535,6 +535,11 @@ typedef struct AVOutputFormat {
>        */
>       int priv_data_size;
>   
> +    /**
> +     * Internal flags. See FF_FMT_FLAG_* in internal.h.
> +     */
> +    int flags_internal;
> +
>       int (*write_header)(struct AVFormatContext *);
>       /**
>        * Write a packet. If AVFMT_ALLOW_FLUSH is set in flags,
> @@ -674,6 +679,11 @@ typedef struct AVInputFormat {
>        */
>       int priv_data_size;
>   
> +    /**
> +     * Internal flags. See FF_FMT_FLAG_* in internal.h.
> +     */
> +    int flags_internal;
> +
>       /**
>        * Tell if a given file has a chance of being parsed as this format.
>        * The buffer provided is guaranteed to be AVPROBE_PADDING_SIZE bytes
>