M4 Supported Codecs

As M4 uses RTPEngine as a Media Proxy, supported codecs are:

rtpengine --codecs
               PCMA: fully supported
               PCMU: fully supported
               G723: fully supported
               G722: fully supported
              QCELP: supported for decoding only
               G729: fully supported
              G729a: fully supported
              speex: fully supported
                GSM: fully supported
               iLBC: not supported
               opus: fully supported
             vorbis: codec supported but lacks RTP definition
                ac3: codec supported but lacks RTP definition
               eac3: codec supported but lacks RTP definition
             ATRAC3: supported for decoding only
            ATRAC-X: supported for decoding only
                AMR: fully supported
             AMR-WB: fully supported
    telephone-event: fully supported
                 CN: fully supported
          PCM-S16LE: codec supported but lacks RTP definition
             PCM-U8: codec supported but lacks RTP definition
                MP3: codec supported but lacks RTP definition