aacenc: add support for encoding 7.1 channel audio

This commit implements support for 7.1 channel audio. There's no
more predefined bitstream channel mappings so going beyond 8 channels
(and 7 channels exactly) will require programmable channel elements,
which is already underway.

libavcodec/aacenc.c

@@ -54,11 +54,12 @@ static void put_audio_specific_config(AVCodecContext *avctx)
 {
     PutBitContext pb;
     AACEncContext *s = avctx->priv_data;
+    int channels = s->channels - (s->channels == 8 ? 1 : 0);
 
     init_put_bits(&pb, avctx->extradata, avctx->extradata_size);
     put_bits(&pb, 5, s->profile+1); //profile
     put_bits(&pb, 4, s->samplerate_index); //sample rate index
-    put_bits(&pb, 4, s->channels);
+    put_bits(&pb, 4, channels);
     //GASpecificConfig
     put_bits(&pb, 1, 0); //frame length - 1024 samples
     put_bits(&pb, 1, 0); //does not depend on core coder
@@ -866,7 +867,7 @@ static av_cold int aac_encode_init(AVCodecContext *avctx)
 
     ERROR_IF(i == 16 || i >= ff_aac_swb_size_1024_len || i >= ff_aac_swb_size_128_len,
              "Unsupported sample rate %d\n", avctx->sample_rate);
-    ERROR_IF(s->channels > AAC_MAX_CHANNELS,
+    ERROR_IF(s->channels > AAC_MAX_CHANNELS || s->channels == 7,
              "Unsupported number of channels: %d\n", s->channels);
     WARN_IF(1024.0 * avctx->bit_rate / avctx->sample_rate > 6144 * s->channels,
              "Too many bits per frame requested, clamping to max\n");

libavcodec/aacenctab.h

@@ -36,7 +36,7 @@
 /** Total number of codebooks, including special ones **/
 #define CB_TOT_ALL 15
 
-#define AAC_MAX_CHANNELS 6
+#define AAC_MAX_CHANNELS 8
 
 extern const uint8_t *ff_aac_swb_size_1024[];
 extern const int      ff_aac_swb_size_1024_len;
@@ -44,13 +44,15 @@ extern const uint8_t *ff_aac_swb_size_128[];
 extern const int      ff_aac_swb_size_128_len;
 
 /** default channel configurations */
-static const uint8_t aac_chan_configs[6][5] = {
-    {1, TYPE_SCE},                               // 1 channel  - single channel element
-    {1, TYPE_CPE},                               // 2 channels - channel pair
-    {2, TYPE_SCE, TYPE_CPE},                     // 3 channels - center + stereo
-    {3, TYPE_SCE, TYPE_CPE, TYPE_SCE},           // 4 channels - front center + stereo + back center
-    {3, TYPE_SCE, TYPE_CPE, TYPE_CPE},           // 5 channels - front center + stereo + back stereo
-    {4, TYPE_SCE, TYPE_CPE, TYPE_CPE, TYPE_LFE}, // 6 channels - front center + stereo + back stereo + LFE
+static const uint8_t aac_chan_configs[AAC_MAX_CHANNELS][6] = {
+    {1, TYPE_SCE},                                         // 1 channel  - single channel element
+    {1, TYPE_CPE},                                         // 2 channels - channel pair
+    {2, TYPE_SCE, TYPE_CPE},                               // 3 channels - center + stereo
+    {3, TYPE_SCE, TYPE_CPE, TYPE_SCE},                     // 4 channels - front center + stereo + back center
+    {3, TYPE_SCE, TYPE_CPE, TYPE_CPE},                     // 5 channels - front center + stereo + back stereo
+    {4, TYPE_SCE, TYPE_CPE, TYPE_CPE, TYPE_LFE},           // 6 channels - front center + stereo + back stereo + LFE
+    {0},                                                   // 7 channels - invalid without PCE
+    {5, TYPE_SCE, TYPE_CPE, TYPE_CPE, TYPE_CPE, TYPE_LFE}, // 8 channels - front center + front stereo + side stereo + back stereo + LFE
 };
 
 /**
@@ -63,6 +65,8 @@ static const uint8_t aac_chan_maps[AAC_MAX_CHANNELS][AAC_MAX_CHANNELS] = {
     { 2, 0, 1, 3 },
     { 2, 0, 1, 3, 4 },
     { 2, 0, 1, 4, 5, 3 },
+    { 0 },
+    { 2, 0, 1, 6, 7, 4, 5, 3 },
 };
 
 /* duplicated from avpriv_mpeg4audio_sample_rates to avoid shared build