libopus: Remap channels using libopus' internal remapping.

This way we can directly remap channels from Opus' channel order to
libav's internal channel order, instead of mapping channels from
Opus' order to Vorbis' order then to libav's order.

Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavcodec/libopusdec.c

@@ -56,28 +56,13 @@ static int opus_error_to_averror(int err)
     }
 }
 
-static inline void reorder(uint8_t *data, unsigned channels, unsigned bps,
-                           unsigned samples, const uint8_t *map)
-{
-    uint8_t tmp[8 * 4];
-    unsigned i;
-
-    av_assert1(channels * bps <= sizeof(tmp));
-    for (; samples > 0; samples--) {
-        for (i = 0; i < channels; i++)
-            memcpy(tmp + bps * i, data + bps * map[i], bps);
-        memcpy(data, tmp, bps * channels);
-        data += bps * channels;
-    }
-}
-
 #define OPUS_HEAD_SIZE 19
 
 static av_cold int libopus_decode_init(AVCodecContext *avc)
 {
     struct libopus_context *opus = avc->priv_data;
     int ret, channel_map = 0, gain_db = 0, nb_streams, nb_coupled;
-    uint8_t mapping_stereo[] = { 0, 1 }, *mapping;
+    uint8_t mapping_arr[8] = { 0, 1 }, *mapping;
 
     avc->sample_rate    = 48000;
     avc->sample_fmt     = avc->request_sample_fmt == AV_SAMPLE_FMT_FLT ?
@@ -103,7 +88,17 @@ static av_cold int libopus_decode_init(AVCodecContext *avc)
         }
         nb_streams = 1;
         nb_coupled = avc->channels > 1;
-        mapping    = mapping_stereo;
+        mapping    = mapping_arr;
+    }
+
+    if (avc->channels > 2 && avc->channels <= 8) {
+        const uint8_t *vorbis_offset = ff_vorbis_channel_layout_offsets[avc->channels - 1];
+        int ch;
+
+        /* Remap channels from vorbis order to libav order */
+        for (ch = 0; ch < avc->channels; ch++)
+            mapping_arr[ch] = mapping[vorbis_offset[ch]];
+        mapping = mapping_arr;
     }
 
     opus->dec = opus_multistream_decoder_create(avc->sample_rate, avc->channels,
@@ -164,14 +159,6 @@ static int libopus_decode(AVCodecContext *avc, void *frame,
         return opus_error_to_averror(nb_samples);
     }
 
-    if (avc->channels > 3 && avc->channels <= 8) {
-        const uint8_t *m = ff_vorbis_channel_layout_offsets[avc->channels - 1];
-        if (avc->sample_fmt == AV_SAMPLE_FMT_S16)
-            reorder(opus->frame.data[0], avc->channels, 2, nb_samples, m);
-        else
-            reorder(opus->frame.data[0], avc->channels, 4, nb_samples, m);
-    }
-
     opus->frame.nb_samples = nb_samples;
     *(AVFrame *)frame = opus->frame;
     *got_frame_ptr = 1;