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

[James Almer]

On 3/29/2021 2:20 PM, Andreas Rheinhardt wrote:
> 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.
>>
> 
> What are your plans for encoders that don't know the final size in
> advance and overallocate?

Keep using av_packet_shrink() like now.

> 
>>>
>>>    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);
>>>   
>>
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