(Almost) Add support for G.729 Annex B

src/audio/audio_decoder.cpp

@@ -572,30 +572,45 @@ t_g729a_audio_decoder::~t_g729a_audio_decoder()
 
 uint16 t_g729a_audio_decoder::get_ptime(uint16 payload_size) const
 {
-	return (payload_size * 8) / (audio_sample_rate(_codec) / 1000);
+	// Account for a possible 2-byte SID frame that will expand to 80
+	// samples juste like any other frame.  The (size+8)/10 expression,
+	// rounded down, results in the total number of frames, SID or not.
+	return (((payload_size + 8) / 10) * 80) / (audio_sample_rate(_codec) / 1000);
 }
 
 uint16 t_g729a_audio_decoder::decode(uint8 *payload, uint16 payload_size,
 		int16 *pcm_buf, uint16 pcm_buf_size)
 {
-	assert((payload_size % 10) == 0);
-	assert(pcm_buf_size >= payload_size*8);
+	// Allow for a 2-byte SID frame at the end of the RTP packet
+	assert(((payload_size % 10) == 0) || ((payload_size % 10) == 2));
+	// See get_ptime() above for an explanation of this expression
+	assert(pcm_buf_size >= (((payload_size + 8) / 10) * 80));
 
-	for (uint16 done = 0; done < payload_size; done += 10)
+	uint8 frame_size = 10;
+	uint16 result_size = 0;
+
+	for (uint16 done = 0; done < payload_size; done += frame_size)
 	{
+		// RFC 3551 mandates that a SID frame be the last in the packet;
+		// its presence can thus be deduced from the payload size.
+		bool is_sid = ((payload_size - done) == 2);
+		frame_size = (is_sid ? 2 : 10);
 #ifdef HAVE_BCG729_ANNEX_B
-		bcg729Decoder(_context, &payload[done], 0, false, false, false, &pcm_buf[done * 8]);
+		bcg729Decoder(_context, &payload[done], 0, false, is_sid, false, &pcm_buf[result_size]);
 #else
-		bcg729Decoder(_context, &payload[done], false, &pcm_buf[done * 8]);
+		bcg729Decoder(_context, &payload[done], false, &pcm_buf[result_size]);
 #endif
+		result_size += 80;
 	}
 
-	return payload_size * 8;
+	return result_size;
 }
 
 bool t_g729a_audio_decoder::valid_payload_size(uint16 payload_size, uint16 sample_buf_size) const
 {
-	return payload_size > 0 && (payload_size % 10) == 0;
+	// Allow for a 2-byte SID frame at the end of the RTP packet
+	return (payload_size > 0) &&
+		(((payload_size % 10) == 0) || ((payload_size % 10) == 2));
 }
 
 uint16 t_g729a_audio_decoder::conceal(int16 *pcm_buf, uint16 pcm_buf_size)

src/audio/audio_encoder.cpp

@@ -476,6 +476,7 @@ t_g729a_audio_encoder::t_g729a_audio_encoder(uint16 payload_id, uint16 ptime, t_
 	: t_audio_encoder(payload_id, ptime, user_config)
 {
 #ifdef HAVE_BCG729_ANNEX_B
+	// Disable G.729B features for the time being
 	_context = initBcg729EncoderChannel(false);
 #else
 	_context = initBcg729EncoderChannel();
@@ -491,22 +492,32 @@ uint16 t_g729a_audio_encoder::encode(int16 *sample_buf, uint16 nsamples,
 		uint8 *payload, uint16 payload_size, bool &silence)
 {
 	assert ((nsamples % 80) == 0);
-	assert (payload_size >= (nsamples/8));
+	assert (payload_size >= ((nsamples / 80) * 10));
 
-	silence = false;
+	uint8 frame_size = 10;
+	uint16 result_size = 0;
 
+	// G.729B TODO: RFC 3551 mandates that a SID frame be the last in the
+	// packet; this could require us to only encode a portion of the
+	// samples, which the current interface does not allow for.
 	for (uint16 done = 0; done < nsamples; done += 80)
 	{
 #ifdef HAVE_BCG729_ANNEX_B
-		uint8 frame_size = 10;
-		bcg729Encoder(_context, &sample_buf[done], &payload[done / 8], &frame_size);
-		assert(frame_size == 10);
+		bcg729Encoder(_context, &sample_buf[done], &payload[result_size], &frame_size);
 #else
-		bcg729Encoder(_context, &sample_buf[done], &payload[done / 8]);
+		bcg729Encoder(_context, &sample_buf[done], &payload[result_size]);
 #endif
+		result_size += frame_size;
 	}
 
-	return nsamples / 8;
+	silence = (result_size == 0);
+
+	// G.729B TODO: In the event that the encoding only resulted in
+	// untransmitted frames, we would return 0 bytes; the caller should be
+	// ready for that outcome.  (At the moment, when sending a keepalive
+	// packet, it would call putData() with len = 0, which is interpreted as
+	// "a default by payload type".)
+	return result_size;
 }
 
 #endif