[FFmpeg-devel] [PATCH v4] avcodec/libfdk-accenc: Add option to set frame length when encoding with libfdk_aac

[Martin Storsjö]

On Thu, 30 Mar 2023, Raphael Schlarb wrote:

> Some specifications require the size of ld/eld frames to be 480 samples
> instead of the default 512. libfdk_aac provides an option to set an alternative
> frame size, but it's not exposed via the ffmpeg interface.
> This patch adds a frame_length option to solve this problem.
>
> Signed-off-by: Raphael Schlarb <info at raphael.schlarb.one>
> ---
> Adjusted according to Martin's suggestion
> libavcodec/libfdk-aacenc.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/libavcodec/libfdk-aacenc.c b/libavcodec/libfdk-aacenc.c
> index eb97e0fb41..954b8e06d0 100644
> --- a/libavcodec/libfdk-aacenc.c
> +++ b/libavcodec/libfdk-aacenc.c
> @@ -55,6 +55,7 @@ typedef struct AACContext {
>     int metadata_mode;
>     AACENC_MetaData metaDataSetup;
>     int delay_sent;
> +    int frame_length;
>
>     AudioFrameQueue afq;
> } AACContext;
> @@ -78,6 +79,7 @@ static const AVOption aac_enc_options[] = {
>     { "comp_profile", "The desired compression profile for AAC DRC", offsetof(AACContext, comp_profile), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 256, AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM },
>     { "comp_target_ref", "Expected target reference level at decoder side in dB (for clipping prevention/limiter)", offsetof(AACContext, comp_target_ref), AV_OPT_TYPE_INT, { .i64 = 0.0 }, -31.75, 0, AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM },
>     { "prog_ref", "The program reference level or dialog level in dB", offsetof(AACContext, prog_ref), AV_OPT_TYPE_INT, { .i64 = 0.0 }, -31.75, 0, AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM },
> +    { "frame_length", "The desired frame length", offsetof(AACContext, frame_length), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1024, AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM },
>     FF_AAC_PROFILE_OPTS
>     { NULL }
> };
> @@ -166,6 +168,15 @@ static av_cold int aac_encode_init(AVCodecContext *avctx)
>         }
>     }
>
> +    if (s->frame_length != -1) {

I would kinda have used > 0 or >= 0 as comparison here, but that's just a 
nitpick (no need to resubmit just for that).

> +        if ((err = aacEncoder_SetParam(s->handle, AACENC_GRANULE_LENGTH,
> +                                       s->frame_length)) != AACENC_OK) {
> +            av_log(avctx, AV_LOG_ERROR, "Unable to set granule length: %s\n",
> +                   aac_get_error(err));
> +            goto error;
> +        }
> +    }
> +

Overall this looks fine to me, thanks!

// Martin