aptx: implement the aptX bluetooth codec

The encoder was reverse engineered from binary library and from
EP0398973B1 patent (long expired).
The decoder was simply deduced from the encoder.

doc/general.texi

@@ -993,6 +993,8 @@ following image formats are supported:
 @item Amazing Studio PAF Audio @tab     @tab  X
 @item Apple lossless audio   @tab  X  @tab  X
     @tab QuickTime fourcc 'alac'
+@item aptX                   @tab  X  @tab  X
+    @tab Used in Bluetooth A2DP
 @item ATRAC1                 @tab     @tab  X
 @item ATRAC3                 @tab     @tab  X
 @item ATRAC3+                @tab     @tab  X

libavcodec/Makefile

@@ -188,6 +188,8 @@ OBJS-$(CONFIG_AMV_ENCODER)             += mjpegenc.o mjpegenc_common.o \
 OBJS-$(CONFIG_ANM_DECODER)             += anm.o
 OBJS-$(CONFIG_ANSI_DECODER)            += ansi.o cga_data.o
 OBJS-$(CONFIG_APE_DECODER)             += apedec.o
+OBJS-$(CONFIG_APTX_DECODER)            += aptx.o
+OBJS-$(CONFIG_APTX_ENCODER)            += aptx.o
 OBJS-$(CONFIG_APNG_DECODER)            += png.o pngdec.o pngdsp.o
 OBJS-$(CONFIG_APNG_ENCODER)            += png.o pngenc.o
 OBJS-$(CONFIG_SSA_DECODER)             += assdec.o ass.o

libavcodec/allcodecs.c

@@ -406,6 +406,7 @@ static void register_all(void)
     REGISTER_DECODER(AMRNB,             amrnb);
     REGISTER_DECODER(AMRWB,             amrwb);
     REGISTER_DECODER(APE,               ape);
+    REGISTER_ENCDEC (APTX,              aptx);
     REGISTER_DECODER(ATRAC1,            atrac1);
     REGISTER_DECODER(ATRAC3,            atrac3);
     REGISTER_DECODER(ATRAC3AL,          atrac3al);

libavcodec/avcodec.h

@@ -632,6 +632,7 @@ enum AVCodecID {
     AV_CODEC_ID_ATRAC3AL,
     AV_CODEC_ID_ATRAC3PAL,
     AV_CODEC_ID_DOLBY_E,
+    AV_CODEC_ID_APTX,
 
     /* subtitle codecs */
     AV_CODEC_ID_FIRST_SUBTITLE = 0x17000,          ///< A dummy ID pointing at the start of subtitle codecs.

libavcodec/codec_desc.c

@@ -2859,6 +2859,13 @@ static const AVCodecDescriptor codec_descriptors[] = {
         .long_name = NULL_IF_CONFIG_SMALL("ADPCM MTAF"),
         .props     = AV_CODEC_PROP_LOSSY,
     },
+    {
+        .id        = AV_CODEC_ID_APTX,
+        .type      = AVMEDIA_TYPE_AUDIO,
+        .name      = "aptx",
+        .long_name = NULL_IF_CONFIG_SMALL("aptX (Audio Processing Technology for Bluetooth)"),
+        .props     = AV_CODEC_PROP_LOSSY,
+    },
 
     /* subtitle codecs */
     {