Re: [FFmpeg-devel] [PATCH] libavcodec/libfdk-aacnc: send encoder delay/padding in packet side data

["Martin Storsjö" <martin@martin.st>]

On Fri, 24 Feb 2023, JonHGee wrote:

> ---
> libavcodec/libfdk-aacenc.c | 27 ++++++++++++++++++++++++++-
> 1 file changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/libavcodec/libfdk-aacenc.c b/libavcodec/libfdk-aacenc.c
> index 54549de473..55d10990e4 100644
> --- a/libavcodec/libfdk-aacenc.c
> +++ b/libavcodec/libfdk-aacenc.c
> @@ -21,6 +21,7 @@
>
> #include "libavutil/channel_layout.h"
> #include "libavutil/common.h"
> +#include "libavutil/intreadwrite.h"
> #include "libavutil/opt.h"
> #include "avcodec.h"
> #include "audio_frame_queue.h"
> @@ -46,6 +47,7 @@ typedef struct AACContext {
>     int latm;
>     int header_period;
>     int vbr;
> +    int delay_sent;
>
>     AudioFrameQueue afq;
> } AACContext;
> @@ -368,7 +370,7 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
>     int out_buffer_identifier = OUT_BITSTREAM_DATA;
>     int out_buffer_size, out_buffer_element_size;
>     void *in_ptr, *out_ptr;
> -    int ret;
> +    int ret, discard_padding;
>     uint8_t dummy_buf[1];
>     AACENC_ERROR err;
>
> @@ -428,6 +430,29 @@ static int aac_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
>     ff_af_queue_remove(&s->afq, avctx->frame_size, &avpkt->pts,
>                        &avpkt->duration);
>
> +    discard_padding = avctx->frame_size - avpkt->duration;
> +    // Check if subtraction resulted in an overflow
> +    if ((discard_padding < avctx->frame_size) != (avpkt->duration > 0)) {
> +        av_log(avctx, AV_LOG_ERROR, "discard padding overflow\n");
> +        av_packet_unref(avpkt);
> +        av_free(avpkt);

I don't think we can or should free the avpkt pointer here (which is 
allocated by the caller).

> +        return AVERROR(EINVAL);
> +    }
> +    if ((!s->delay_sent && avctx->initial_padding > 0) || discard_padding > 0) {
> +        uint8_t *side_data =
> +            av_packet_new_side_data(avpkt, AV_PKT_DATA_SKIP_SAMPLES, 10);
> +        if (!side_data) {
> +            av_packet_unref(avpkt);
> +            av_free(avpkt);
> +            return AVERROR(ENOMEM);
> +        }
> +        if (!s->delay_sent) {
> +            AV_WL32(side_data, avctx->initial_padding);
> +            s->delay_sent = 1;
> +        }
> +        AV_WL32(side_data + 4, discard_padding);
> +    }
> +

Other than that, this seems reasonable. There's a bunch of stylistic 
choices that I'd do slightly differently here, but this seems to match 
existing code in libavcodec/libmp3lame.c, so it's probably ok to keep it 
matching.

// Martin

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