[FFmpeg-devel] Patch to close ticket 2873 (enhancement)

[Nicolas George]

Le septidi 17 nivôse, an CCXXII, kad kadmandu a écrit :
> 2014/1/6 kad kadmandu <kadmandux at gmail.com>

Please remember not to top-post.

> diff -r -u a/libavformat/avformat.h b/libavformat/avformat.h

"git format-patch" or "git send-email" is the recommended way of preparing
patches, since it allow for easy inclusion, with author information and so.

> --- a/libavformat/avformat.h	2014-01-06 01:10:24.000000000 +0000
> +++ b/libavformat/avformat.h	2014-01-06 01:19:31.000000000 +0000
> @@ -1484,6 +1484,9 @@
>   * @}
>   */
>  
> +int av_compare_streams(const void *st1, const void *st2);
> +void av_sort_streams_by_id(AVFormatContext *s);

I really think these should not be public. Especially the first one, with
its strange types for arguments (yes, I know how qsort works).

And if they are public, the documentation is missing.

> +
>  
>  #if FF_API_ALLOC_OUTPUT_CONTEXT
>  /**
> diff -r -u a/libavformat/utils.c b/libavformat/utils.c
> --- a/libavformat/utils.c	2014-01-06 01:10:09.000000000 +0000
> +++ b/libavformat/utils.c	2014-01-06 02:04:01.000000000 +0000
> @@ -3215,6 +3215,11 @@
>      if(ic->pb)
>          av_log(ic, AV_LOG_DEBUG, "After avformat_find_stream_info() pos: %"PRId64" bytes read:%"PRId64" seeks:%d frames:%d\n",
>                 avio_tell(ic->pb), ic->pb->bytes_read, ic->pb->seek_count, count);
> +

> +    /* Reorder streams if the format requires it.*/
> +    if (ic->ctx_flags & AVFMTCTX_NOHEADER)
> +	av_sort_streams_by_id(ic);

Did you check that doing that actually works? Right there, I can see that
you will leave the AVStream.index inconsistent, and I suspect that the
packets already read by avformat_find_stream_info() will be inconsistent
too.

Also, I do not think that it should be done for MPEG-TS, where the streams
are actually declared in a particular order.

Last: what happens if the application has read frames by itself before
calling avformat_find_stream_info()? In that case, I am afraid the order of
the streams will change underfoot.

> +
>      return ret;
>  }
>  
> @@ -3472,6 +3477,20 @@
>      return st;
>  }
>  
> +int av_compare_streams(const void *st1, const void *st2)
> +{
> +	return (((*(AVStream **)st1)->id > (*(AVStream **)st2)->id) ?  1 : 
> +		((*(AVStream **)st1)->id < (*(AVStream **)st2)->id) ? -1 : 0);
> +}
> +
> +void av_sort_streams_by_id(AVFormatContext *s)
> +{
> +	qsort((void *)s->streams, s->nb_streams, sizeof(s->streams[0]), av_compare_streams);
> +	/*Adjust the indexes */
> +	for (int i=0;i<s->nb_streams;i++)
> +		s->streams[i]->index = i;
> +}
> +
>  AVProgram *av_new_program(AVFormatContext *ac, int id)
>  {
>      AVProgram *program=NULL;

Regards,

-- 
  Nicolas George
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