add encoding codec - alaw,mulaw,g729

cgo/ffmpeg/audio.go

@@ -587,7 +587,7 @@ func (self *AudioDecoder) Decode(pkt []byte) (gotframe bool, frame av.AudioFrame
 
 	if ff.codecCtx == nil || &pkt[0] == nil {
 		err = fmt.Errorf("ffmpeg: Decode ff.codecCtx NULL or pkg NULL")
-		return 
+		return
 	}
 
 	cerr := C.decode(ff.codecCtx, ff.frame, (*C.uchar)(unsafe.Pointer(&pkt[0])), C.int(len(pkt)), &cgotframe)
@@ -620,6 +620,12 @@ func NewAudioEncoderByCodecType(typ av.CodecType) (enc *AudioEncoder, err error)
 	switch typ {
 	case av.AAC:
 		id = C.AV_CODEC_ID_AAC
+	case av.PCM_ALAW:
+		id = C.AV_CODEC_ID_PCM_ALAW
+	case av.PCM_MULAW:
+		id = C.AV_CODEC_ID_PCM_MULAW
+	case av.G729:
+		id = C.AV_CODEC_ID_G729
 
 	default:
 		err = fmt.Errorf("ffmpeg: cannot find encoder codecType=%d", typ)