On 1/2/2018 1:24 PM, zhangjiejun1...@gmail.com wrote:
> From: Jiejun Zhang <zhangjiejun1...@gmail.com>
>
> This fixes #6940
>
> 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. Retaining a frame reference solves this problem.
> ---
> libavcodec/audiotoolboxenc.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/libavcodec/audiotoolboxenc.c b/libavcodec/audiotoolboxenc.c
> index 71885d1530..5d3a746348 100644
> --- a/libavcodec/audiotoolboxenc.c
> +++ b/libavcodec/audiotoolboxenc.c
> @@ -48,6 +48,8 @@ typedef struct ATDecodeContext {
> AudioFrameQueue afq;
> int eof;
> int frame_size;
> +
> + AVFrame* encoding_frame;
> } ATDecodeContext;
>
> static UInt32 ffat_get_format_id(enum AVCodecID codec, int profile)
> @@ -442,6 +444,10 @@ static av_cold int ffat_init_encoder(AVCodecContext
> *avctx)
>
> ff_af_queue_init(avctx, &at->afq);
>
> + at->encoding_frame = av_frame_alloc();
> + if (!at->encoding_frame)
> + return AVERROR(ENOMEM);
> +
> return 0;
> }
>
> @@ -453,6 +459,7 @@ static OSStatus ffat_encode_callback(AudioConverterRef
> converter, UInt32 *nb_pac
> AVCodecContext *avctx = inctx;
> ATDecodeContext *at = avctx->priv_data;
> AVFrame *frame;
> + int ret;
>
> if (!at->frame_queue.available) {
> if (at->eof) {
> @@ -475,6 +482,10 @@ static OSStatus ffat_encode_callback(AudioConverterRef
> converter, UInt32 *nb_pac
> if (*nb_packets > frame->nb_samples)
> *nb_packets = frame->nb_samples;
>
> + av_frame_unref(at->encoding_frame);
> + if ((ret = av_frame_ref(at->encoding_frame, frame)) < 0)
> + return ret;
Wouldn't you have to set nb_packets to 0 in case of failure? And for a
non libav* callback function maybe this shouldn't return an AVERROR(),
but just 1 instead.
Also, look at audiotoolboxdec.c, where the reference (packet there
instead of frame) is created right before calling
AudioConverterFillComplexBuffer(), as it can fail. Maybe you can do
something like that instead.
> +
> ff_bufqueue_add(avctx, &at->used_frame_queue, frame);
>
> return 0;
> @@ -565,6 +576,7 @@ 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);
> + av_frame_free(&at->encoding_frame);
> return 0;
> }
>
>
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