[FFmpeg-devel] [PATCH] lavc/audiotoolboxenc: fix noise in encoded audio

[Jiejun Zhang]

On Tue, Jan 2, 2018 at 10:37 PM, wm4 <nfxjfg at googlemail.com> wrote:
> On Tue, 2 Jan 2018 22:27:49 +0800
> Jiejun Zhang <zhangjiejun1992 at gmail.com> wrote:
>
>> On Tue, Jan 2, 2018 at 8:03 PM, Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
>> > 2018-01-02 8:52 GMT+01:00  <zhangjiejun1992 at gmail.com>:
>> >
>> >> @@ -565,6 +579,10 @@ static av_cold int ffat_close_encoder(AVCodecContext *avctx)
>> >>      ff_bufqueue_discard_all(&at->frame_queue);
>> >>      ff_bufqueue_discard_all(&at->used_frame_queue);
>> >>      ff_af_queue_close(&at->afq);
>> >> +    if (at->audio_data_buf_size > 0) {
>> >> +        at->audio_data_buf_size = 0;
>> >> +        av_free(at->audio_data_buf);
>> >> +    }
>> >
>> > The if() looks unnecessary.
>>
>> Yes. I'll remove it. Thanks for pointing it out.
>>
>> > Could you explain what this patch changes?
>> > From a quick look, until now a buffer a was used with a calculated size x.
>> > After the patch, a buffer b with the same calculated size x is allocated,
>> > and x bytes are copied from a to b.
>> > What do I miss?
>>
>> Although undocumented, AudioToolbox seems to require the data supplied
>> by the callback (i.e. ffat_encode_callback) being unchanged until the
>> next time the callback is called. In the old implementation, the
>> AVBuffer backing the frame is recycled after the frame is freed, and
>> somebody else (maybe the decoder) will write into the AVBuffer and
>> change the data. AudioToolbox then encodes some wrong data and noise
>> is produced. Copying the data to a separate buffer solves this
>> problem.
>
> This should be in the commit message.

Done. Submitting v2