[FFmpeg-devel] [PATCH 2/2] avcodec/ac3enc: Avoid needlessly copying encoded packets around

[James Almer]

On 3/29/2021 2:12 PM, Andreas Rheinhardt wrote:
> AC-3 and EAC-3 are codecs whose packet sizes are known in advance,
> so one can use the min_size parameter of ff_alloc_packet2() to
> allocate exactly this amount. This avoids a memcpy later in
> av_packet_make_refcounted() in encode_simple_internal().
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
> ---
> Is there actually a reason not to use av_new_packet() (or
> ff_get_encode_buffer()) directly?

I'm waiting for the bump when avcodec_encode_*() are removed before 
making most encoders DR1, and thus use ff_get_encode_buffer(). And that 
includes this one.

This patch LGTM, but it may not be worth applying if it's going to be 
changed again very soon.

> 
>   libavcodec/ac3enc.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/ac3enc.c b/libavcodec/ac3enc.c
> index 4cfd0afe12..fc4d45651d 100644
> --- a/libavcodec/ac3enc.c
> +++ b/libavcodec/ac3enc.c
> @@ -1759,7 +1759,8 @@ int ff_ac3_encode_frame_common_end(AVCodecContext *avctx, AVPacket *avpkt,
>   
>       ac3_quantize_mantissas(s);
>   
> -    if ((ret = ff_alloc_packet2(avctx, avpkt, s->frame_size, 0)) < 0)
> +    ret = ff_alloc_packet2(avctx, avpkt, s->frame_size, s->frame_size);
> +    if (ret < 0)
>           return ret;
>       ac3_output_frame(s, avpkt->data);
>   
>