[FFmpeg-devel] [PATCH] lavc/decode: do not use a context variable for function-local data

[James Almer]

On 5/22/2020 1:56 PM, Anton Khirnov wrote:
> ---
>  libavcodec/decode.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
> index f3327d74af..dbecdf3f46 100644
> --- a/libavcodec/decode.c
> +++ b/libavcodec/decode.c
> @@ -586,6 +586,7 @@ static int decode_receive_frame_internal(AVCodecContext *avctx, AVFrame *frame)
>  int attribute_align_arg avcodec_send_packet(AVCodecContext *avctx, const AVPacket *avpkt)
>  {
>      AVCodecInternal *avci = avctx->internal;
> +    AVPacket buffer_pkt = { NULL };
>      int ret;
>  
>      if (!avcodec_is_open(avctx) || !av_codec_is_decoder(avctx->codec))
> @@ -597,16 +598,15 @@ int attribute_align_arg avcodec_send_packet(AVCodecContext *avctx, const AVPacke
>      if (avpkt && !avpkt->size && avpkt->data)
>          return AVERROR(EINVAL);
>  
> -    av_packet_unref(avci->buffer_pkt);
>      if (avpkt && (avpkt->data || avpkt->side_data_elems)) {
> -        ret = av_packet_ref(avci->buffer_pkt, avpkt);
> +        ret = av_packet_ref(&buffer_pkt, avpkt);
>          if (ret < 0)
>              return ret;
>      }
>  
> -    ret = av_bsf_send_packet(avci->bsf, avci->buffer_pkt);
> +    ret = av_bsf_send_packet(avci->bsf, &buffer_pkt);
>      if (ret < 0) {
> -        av_packet_unref(avci->buffer_pkt);
> +        av_packet_unref(&buffer_pkt);
>          return ret;
>      }

What's the gain here? You're not removing the context variable since
it's used in the encode framework as well, and you're introducing a
stack AVPacket (that, while harmless, is not even properly initialized).