[FFmpeg-devel] [PATCH v2] Add option to set frame length when encoding with libfdk_aac

From: Raphael Schlarb <info@raphael.schlarb.one>
To: ffmpeg-devel@ffmpeg.org
Cc: Raphael Schlarb <info@raphael.schlarb.one>
Subject: [FFmpeg-devel] [PATCH v2] Add option to set frame length when encoding with libfdk_aac
Date: Mon, 27 Mar 2023 16:37:05 +0200
Message-ID: <20230327143705.2371-1-info@raphael.schlarb.one> (raw)
In-Reply-To: <dacdb965-e2e4-abbf-3da5-31f2498f5579@gmail.com>

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.
---
Thank you, this really makes more sense. Here an updated version.
 libavcodec/libfdk-aacenc.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/libavcodec/libfdk-aacenc.c b/libavcodec/libfdk-aacenc.c
index eb97e0fb41..93c26ee082 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 = 1024 }, 120, 1024, AV_OPT_FLAG_AUDIO_PARAM | AV_OPT_FLAG_ENCODING_PARAM },
     FF_AAC_PROFILE_OPTS
     { NULL }
 };
@@ -166,6 +168,18 @@ static av_cold int aac_encode_init(AVCodecContext *avctx)
         }
     }
 
+    if (s->frame_length == 1024 &&
+        (aot == FF_PROFILE_AAC_LD + 1 || aot == FF_PROFILE_AAC_ELD + 1)) {
+        s->frame_length = 512;
+    }
+
+    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;
+    }
+
     if ((err = aacEncoder_SetParam(s->handle, AACENC_SAMPLERATE,
                                    avctx->sample_rate)) != AACENC_OK) {
         av_log(avctx, AV_LOG_ERROR, "Unable to set the sample rate %d: %s\n",
-- 
2.40.0

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