aacdec: add support for dual mono in Japanese DTV

Japanese DTV uses some non standard extensions in AAC audio.
One example is 'dual mono', which combines two independent
audio into one stereo stream, storing them in left and right channels
respectively.  Historically, dual mono audio has been used for
multi-lingual audio, one for local/native language, and another for english,
and usually the "main" (local language) channel should be output without
any user interactions.

The frames of those dual mono audio are allowed to set
ADTS channel_config field to 0, and just contain two SCE's *WITHOUT* PCE,
which is a non standard extension by Japanese DTV standard.
(ref. ARIB STD-B32 PartII 5.2.3)

This patch adds an AVPacket side data, AV_PKT_DATA_JP_DUALMONO,
which indicates that the AVPacket is likely to contain an audio frame
with the above dual mono extension, and has the parameter to specify
the desired channel selection in that case.
It also makes aacdec to detect dual mono and output just the desired
channel when this side data is attached.

Signed-off-by: Akihiro Tsukada <atsukada@users.sourceforge.net>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

1 files changed, 9 insertions, 0 deletions

diff --git a/libavcodec/aac.h b/libavcodec/aac.h
index 29ba2f1402..a1e91b09b6 100644
--- a/libavcodec/aac.h
+++ b/libavcodec/aac.h
@@ -304,6 +304,15 @@ typedef struct {
     float *output_data[MAX_CHANNELS];                 ///< Points to each element's 'ret' buffer (PCM output).
     /** @} */
 
+
+    /**
+     * @name Japanese DTV specific extension
+     * @{
+     */
+    int enable_jp_dmono; ///< enable japanese DTV specific 'dual mono'
+    int dmono_mode;      ///< select the channel to decode in dual mono.
+    /** @} */
+
     DECLARE_ALIGNED(32, float, temp)[128];
 
     OutputConfiguration oc[2];