Index: pjproject/trunk/pjmedia/include/pjmedia-codec/passthrough.h
===================================================================
--- pjproject/trunk/pjmedia/include/pjmedia-codec/passthrough.h	(revision 2875)
+++ pjproject/trunk/pjmedia/include/pjmedia-codec/passthrough.h	(revision 3083)
@@ -34,15 +34,186 @@
  * @{
  *
- * This section describes functions to register and register passthrough 
+ * This section describes functions to initialize and register passthrough 
  * codecs factory to the codec manager. After the codec factory has been 
  * registered, application can use @ref PJMEDIA_CODEC API to manipulate 
- * the codec. This codec factory contains various codecs, e.g: G.729, iLBC,
- * AMR, and G.711.
- *
- * Passthrough codecs are codecs wrapper that does not perform encoding 
- * or decoding, it just pack and parse encoded audio data from/into RTP 
+ * the codec.
+ *
+ * Passthrough codecs are codecs wrapper that does NOT perform encoding 
+ * or decoding, it just PACK and PARSE encoded audio data from/into RTP 
  * payload. This will accomodate pjmedia ports which work with encoded
  * audio data, e.g: encoded audio files, sound device with capability
  * of playing/recording encoded audio data.
+ *
+ * This codec factory contains various codecs, i.e: G.729, iLBC,
+ * AMR, and G.711.
+ *
+ *
+ * \section pjmedia_codec_passthrough_g729 Passthrough G.729
+ *
+ * G.729 supports 16-bit PCM audio signal with sampling rate 8000Hz, 
+ * frame length 10ms, and resulting in bitrate 8000bps.
+ *
+ * \subsection codec_setting Codec Settings
+ *
+ * General codec settings for this codec such as VAD and PLC can be 
+ * manipulated through the <tt>setting</tt> field in #pjmedia_codec_param. 
+ * Please see the documentation of #pjmedia_codec_param for more info.
+ *
+ * Note that G.729 VAD status should be signalled in SDP, see more
+ * description below.
+ *
+ * \subsubsection annexb Annex B
+ *
+ * The capability of VAD/DTX is specified in Annex B.
+ *
+ * By default, Annex B is enabled. This default setting of Annex B can 
+ * be modified using #pjmedia_codec_mgr_set_default_param().
+ *
+ * In #pjmedia_codec_param, Annex B is configured via VAD setting and
+ * format parameter "annexb" in the SDP "a=fmtp" attribute in
+ * decoding fmtp field. Valid values are "yes" and "no",
+ * the implementation default is "yes". When this parameter is omitted
+ * in the SDP, the value will be "yes" (RFC 4856 Section 2.1.9).
+ *
+ * Here is an example of modifying default setting of Annex B to
+ * be disabled using #pjmedia_codec_mgr_set_default_param():
+ \code
+    pjmedia_codec_param param;
+
+    pjmedia_codec_mgr_get_default_param(.., &param);
+    ...
+    // Set VAD
+    param.setting.vad = 0;
+    // Set SDP format parameter
+    param.setting.dec_fmtp.cnt = 1;
+    param.setting.dec_fmtp.param[0].name = pj_str("annexb");
+    param.setting.dec_fmtp.param[0].val  = pj_str("no");
+    ...
+    pjmedia_codec_mgr_set_default_param(.., &param);
+ \endcode
+ *
+ * \note
+ * The difference of Annex B status in SDP offer/answer may be considered as 
+ * incompatible codec in SDP negotiation.
+ *
+ * 
+ * \section pjmedia_codec_passthrough_ilbc Passthrough iLBC
+ *
+ * The iLBC codec is developed by Global IP Solutions (GIPS), formerly 
+ * Global IP Sound. The iLBC offers low bitrate and graceful audio quality 
+ * degradation on frame losses.
+ *
+ * The iLBC codec supports 16-bit PCM audio signal with sampling rate of 
+ * 8000Hz operating at two modes: 20ms and 30ms frame length modes, resulting
+ * in bitrates of 15.2kbps for 20ms mode and 13.33kbps for 30ms mode.
+ *
+ * \subsection codec_setting Codec Settings
+ *
+ * General codec settings for this codec such as VAD and PLC can be 
+ * manipulated through the <tt>setting</tt> field in #pjmedia_codec_param. 
+ * Please see the documentation of #pjmedia_codec_param for more info.
+ *
+ * \subsubsection mode Mode
+ *
+ * The default mode should be set upon initialization, see
+ * #pjmedia_codec_passthrough_init2(). After the codec is initialized, the
+ * default mode can be modified using #pjmedia_codec_mgr_set_default_param().
+ *
+ * In #pjmedia_codec_param, iLBC mode can be set by specifying SDP
+ * format parameter "mode" in the SDP "a=fmtp" attribute for decoding
+ * direction. Valid values are "20" and "30" (for 20ms and 30ms mode 
+ * respectively).
+ *
+ * Here is an example to set up #pjmedia_codec_param to use mode 20ms:
+ *  \code
+    pjmedia_codec_param param;
+    ...
+    // setting iLBC mode in SDP
+    param.setting.dec_fmtp.cnt = 1;
+    param.setting.dec_fmtp.param[0].name = pj_str("mode");
+    param.setting.dec_fmtp.param[0].val  = pj_str("20");
+    ...
+ \endcode
+ *
+ *
+ * \section pjmedia_codec_passthrough_amr Passthrough AMR
+ *
+ * IPP AMR supports 16-bit PCM audio signal with sampling rate 8000Hz,
+ * 20ms frame length and producing various bitrates that ranges from 4.75kbps
+ * to 12.2kbps.
+ *
+ * \subsection codec_setting Codec Settings
+ *
+ * General codec settings for this codec such as VAD and PLC can be 
+ * manipulated through the <tt>setting</tt> field in #pjmedia_codec_param. 
+ * Please see the documentation of #pjmedia_codec_param for more info.
+ *
+ * \subsubsection bitrate Bitrate
+ *
+ * By default, encoding bitrate is 7400bps. This default setting can be 
+ * modified using #pjmedia_codec_mgr_set_default_param() by specifying 
+ * prefered AMR bitrate in field <tt>info::avg_bps</tt> of 
+ * #pjmedia_codec_param. Valid bitrates could be seen in 
+ * #pjmedia_codec_amrnb_bitrates.
+ *
+ * \subsubsection payload_format Payload Format
+ *
+ * There are two AMR payload format types, bandwidth-efficient and
+ * octet-aligned. Default setting is using octet-aligned. This default payload
+ * format can be modified using #pjmedia_codec_mgr_set_default_param().
+ *
+ * In #pjmedia_codec_param, payload format can be set by specifying SDP 
+ * format parameters "octet-align" in the SDP "a=fmtp" attribute for 
+ * decoding direction. Valid values are "0" (for bandwidth efficient mode)
+ * and "1" (for octet-aligned mode).
+ *
+ * \subsubsection mode_set Mode-Set
+ * 
+ * Mode-set is used for restricting AMR modes in decoding direction.
+ *
+ * By default, no mode-set restriction applied. This default setting can be 
+ * be modified using #pjmedia_codec_mgr_set_default_param().
+ *
+ * In #pjmedia_codec_param, mode-set could be specified via format parameters
+ * "mode-set" in the SDP "a=fmtp" attribute for decoding direction. Valid 
+ * value is a comma separated list of modes from the set 0 - 7, e.g: 
+ * "4,5,6,7". When this parameter is omitted, no mode-set restrictions applied.
+ *
+ * Here is an example of modifying AMR default codec param:
+ \code
+    pjmedia_codec_param param;
+
+    pjmedia_codec_mgr_get_default_param(.., &param);
+    ...
+    // set default encoding bitrate to the highest 12.2kbps
+    param.info.avg_bps = 12200;
+
+    // restrict decoding bitrate to 10.2kbps and 12.2kbps only
+    param.setting.dec_fmtp.param[0].name = pj_str("mode-set");
+    param.setting.dec_fmtp.param[0].val  = pj_str("6,7");
+
+    // also set to use bandwidth-efficient payload format
+    param.setting.dec_fmtp.param[1].name = pj_str("octet-align");
+    param.setting.dec_fmtp.param[1].val  = pj_str("0");
+
+    param.setting.dec_fmtp.cnt = 2;
+    ...
+    pjmedia_codec_mgr_set_default_param(.., &param);
+ \endcode
+ * 
+ *
+ * \section pjmedia_codec_passthrough_g711 Passthrough G.711
+ *
+ * The G.711 is an ultra low complexity codecs and in trade-off it results
+ * in high bitrate, i.e: 64kbps for 16-bit PCM with sampling rate 8000Hz.
+ *
+ * The factory contains two main compression algorithms, PCMU/u-Law and 
+ * PCMA/A-Law.
+ *
+ * \subsection codec_setting Codec Settings
+ *
+ * General codec settings for this codec such as VAD and PLC can be 
+ * manipulated through the <tt>setting</tt> field in #pjmedia_codec_param. 
+ * Please see the documentation of #pjmedia_codec_param for more info.
  */
 
@@ -79,5 +250,5 @@
  *
  * @param endpt	    The pjmedia endpoint.
- * @param setting   The settings, see @pjmedia_codec_passthrough_setting.
+ * @param setting   The settings.
  *
  * @return	    PJ_SUCCESS on success.
