Re: [FFmpeg-devel] [PATCH] avcodec/avcodec: don't uninitialize ch_layout in avcodec_close()

[James Almer <jamrial@gmail.com>]

On 3/20/2022 2:03 PM, James Almer wrote:
> On 3/19/2022 10:47 AM, Anton Khirnov wrote:
>> Quoting James Almer (2022-03-19 04:04:07)
>>> The function is not meant to clear codec parameters, and the lavf 
>>> demux code
>>> relies on this behavior.
>>
>> Maybe it shouldn't?
>>
>> Which code is it exactly?
> 
> The parser included by demux.c. That file calls avcodec_close() in 
> certain situations, but the avctx is still used when calling 
> av_parser_parse2() as it's expected that all the parameters are left 
> intact, and all were until 327efa6633, where avctx->ch_layout started 
> being uninitialized, and it shouldn't.

An alternative is

> diff --git a/libavformat/demux.c b/libavformat/demux.c
> index c1c9422ac0..c14e44cb07 100644
> --- a/libavformat/demux.c
> +++ b/libavformat/demux.c
> @@ -2957,6 +2957,7 @@ find_stream_info_err:
>              av_freep(&sti->info);
>          }
>          avcodec_close(sti->avctx);
> +        avcodec_parameters_to_context(sti->avctx, st->codecpar);
>          av_bsf_free(&sti->extract_extradata.bsf);
>      }
>      if (ic->pb) {

Which works around this specific issue, but either way, 
avcodec_close(avctx) should not nuke avctx->ch_layout.
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