[FFmpeg-devel] [PATCH v2 06/10] avcodec/aptx: Use AVCodecContext.frame_size according to the API

[Andreas Rheinhardt]

Hendrik Leppkes:
> On Tue, Aug 31, 2021 at 4:22 PM Hendrik Leppkes <h.leppkes at gmail.com> wrote:
>>
>> On Tue, Aug 31, 2021 at 2:44 PM Andreas Rheinhardt
>> <andreas.rheinhardt at outlook.com> wrote:
>>>
>>> Currently the APTX (HD) codecs set frame_size if unset and check
>>> whether it is divisible by block_size (corresponding to block_align
>>> as used by other codecs). But this is based upon a misunderstanding
>>> of the API: frame_size is not in bytes, but in samples.*
>>>
>>> Said value is also not intended to be set by the user at all,
>>> but set by encoders and (possibly) decoders if the number of channels
>>> in a frame is constant. The latter condition is not fulfilled here,
>>> so only set it for encoders to the value that it already had for APTX:
>>> 1024 samples (per channel).
>>>
>>> *: If it were needed to check said value, one would need to check
>>> for it to be divisible by four (four samples correspond to one block
>>> of block_size bytes).
>>>
>>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>
>>> ---
>>>  libavcodec/aptx.c | 10 ++--------
>>>  1 file changed, 2 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/libavcodec/aptx.c b/libavcodec/aptx.c
>>> index 3aeee1907c..97397aca68 100644
>>> --- a/libavcodec/aptx.c
>>> +++ b/libavcodec/aptx.c
>>> @@ -515,14 +515,8 @@ av_cold int ff_aptx_init(AVCodecContext *avctx)
>>>      s->hd = avctx->codec->id == AV_CODEC_ID_APTX_HD;
>>>      s->block_size = s->hd ? 6 : 4;
>>>
>>> -    if (avctx->frame_size == 0)
>>> -        avctx->frame_size = 256 * s->block_size;
>>> -
>>> -    if (avctx->frame_size % s->block_size) {
>>> -        av_log(avctx, AV_LOG_ERROR,
>>> -               "Frame size must be a multiple of %d samples\n", s->block_size);
>>> -        return AVERROR(EINVAL);
>>> -    }
>>> +    if (av_codec_is_encoder(avctx->codec))
>>> +        avctx->frame_size = 1024;
>>>
>>
>> s->block_size can be 6 for HD or 4 for non-HD, making the default
>> frame_size not always 1024 before this change, thus a change in
>> behavior for aptx HD. Is this intended?
>>
> 
> Nevermind, I now figured out what your commit message means. It wasn't
> extremely clear.
> 
I reread it and still don't get what is unclear. Could you elaborate (or
even suggest changes)?

- Andreas