avcodec/libfdk-accenc: Add option to set frame length when encoding with libfdk_aac

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@raphael.schlarb.one>
Reviewed-by: Martin Storsjö <martin@martin.st>
Signed-off-by: James Almer <jamrial@gmail.com>

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 >= 0) {
+        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",

libavcodec/version.h

@@ -30,7 +30,7 @@
 #include "version_major.h"
 
 #define LIBAVCODEC_VERSION_MINOR   7
-#define LIBAVCODEC_VERSION_MICRO 100
+#define LIBAVCODEC_VERSION_MICRO 101
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
                                                LIBAVCODEC_VERSION_MINOR, \