Re: [FFmpeg-devel] [PATCH 2/3] avcodec/avcodec: don't free coded_side_data in ff_codec_close() when decoding

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

James Almer:
> It's a user-set parameter shared with AVCodecParameters, so it should only
> be freed by avcodec_free_context().
> 
> Signed-off-by: James Almer <jamrial@gmail.com>
> ---
>  libavcodec/avcodec.c | 11 ++++++-----
>  libavcodec/options.c |  4 ++++
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/libavcodec/avcodec.c b/libavcodec/avcodec.c
> index fc8a40e4db..e560efff6a 100644
> --- a/libavcodec/avcodec.c
> +++ b/libavcodec/avcodec.c
> @@ -458,11 +458,12 @@ av_cold void ff_codec_close(AVCodecContext *avctx)
>  
>          av_freep(&avctx->internal);
>      }
> -
> -    for (i = 0; i < avctx->nb_coded_side_data; i++)
> -        av_freep(&avctx->coded_side_data[i].data);
> -    av_freep(&avctx->coded_side_data);
> -    avctx->nb_coded_side_data = 0;
> +    if (av_codec_is_encoder(avctx->codec)) {
> +        for (i = 0; i < avctx->nb_coded_side_data; i++)
> +            av_freep(&avctx->coded_side_data[i].data);
> +        av_freep(&avctx->coded_side_data);
> +        avctx->nb_coded_side_data = 0;
> +    }
>  
>      av_buffer_unref(&avctx->hw_frames_ctx);
>      av_buffer_unref(&avctx->hw_device_ctx);
> diff --git a/libavcodec/options.c b/libavcodec/options.c
> index 0c3b40a186..7c32a71275 100644
> --- a/libavcodec/options.c
> +++ b/libavcodec/options.c
> @@ -177,6 +177,10 @@ void avcodec_free_context(AVCodecContext **pavctx)
>      av_freep(&avctx->inter_matrix);
>      av_freep(&avctx->rc_override);
>      av_channel_layout_uninit(&avctx->ch_layout);
> +    for (int i = 0; i < avctx->nb_coded_side_data; i++)
> +        av_freep(&avctx->coded_side_data[i].data);
> +    av_freep(&avctx->coded_side_data);
> +    avctx->nb_coded_side_data = 0;
>      av_frame_side_data_free(
>          &avctx->decoded_side_data, &avctx->nb_decoded_side_data);
>  

1. ff_codec_close() already has an "if is_encoder" branch, it does not
need another one.
2. The code in ff_codec_close() will be redundant as soon as
FF_API_AVCODEC_CLOSE is no more, so it should be inside
FF_API_AVCODEC_CLOSE.
3. The documentation of this field does not mention ownership, but given
that this field existed for a long time lavc's previous behaviour
established the implicit contract that lavc will free this in
avcodec_close(). You are breaking this implicit contract for no good
reason apart from this new principle that user-set stuff shared with
AVCodecParameters should not be freed in avcodec_close(). Which is crazy
given that the relevant AVCodecParameters field has only been added
recently.

- Andreas

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