mediasoup-sdp-converter.py

#
# Utility functions for converting an sdp textual format to/from MediaSoup format
#

def sdpToMediasoup(text, config):
    """
        Converts an SDP textual description used by GStreamer into the oRTP 
        format used by MediaSoup

        :param text: The SDP text
        :param config: The configuration to use:
            {
              bitrate: Number                # the maximum video bitrate
              simulcast: false|true          # if simulcast should be enabled
            }
        :return: the oRTP object
    """
    mediasoupConfig = {
        'dtlsParameters': {
            'role': 'server',
            'fingerprints': [{
                'algorithm': '',
                'value': ''
            }]
        },
    }
    section = {}
    encoding = {}
    encodingScale = 1
    text = text.split('\n')
    for line in text:
        line = line.strip()
        if line.startswith('a=fingerprint:'):
            algorithm, value = line.replace('a=fingerprint:', '').split()
            mediasoupConfig['dtlsParameters']['fingerprints'][0]['algorithm'] = algorithm
            mediasoupConfig['dtlsParameters']['fingerprints'][0]['value'] = value
        elif line.startswith('m=video '):
            # already found 1 video, add encoding
            if mediasoupConfig.get('video'):
                encodingScale = max(1, int(encodingScale / 2))
                encoding = {
                    'ssrc': '',
                    'active': True,
                    'maxBitrate': int(config['bitrate'] * 1000 / encodingScale),
                    'scaleResolutionDownBy': encodingScale,
                    'scalabilityMode': 'S1T1',
                }
                mediasoupConfig['video']['encodings'].append(encoding)
            else:
                mediasoupConfig['video'] = { 
                    'kind': 'video',
                    # set some default values, overridden by a=rtpmap sections
                    'codecs': [{
                        'name': 'VP8',
                        'mimeType': 'video/VP8',
                        'clockRate': 90000,
                        'payloadType': int(line.split(' ')[-1]),
                        'channels': 1,
                        'rtcpFeedback': [],
                        'parameters': {},
                    }],
                    'headerExtensions': [],
                    'mid': None,
                    'encodings': [{ 'ssrc': '' }]
                }
                section = mediasoupConfig['video']
                encoding = mediasoupConfig['video']['encodings'][0]
                # if simulcast, set the lower level encoding parameters
                if config.get('simulcast'):
                    encodingScale = 4
                    encoding.update({
                        'active': True,
                        'maxBitrate': int(config['bitrate'] * 1000 / encodingScale),
                        'scaleResolutionDownBy': encodingScale,
                        'scalabilityMode': 'S1T1',
                    })
        elif line.startswith('m=audio '):
            mediasoupConfig['audio'] = {
                'kind': 'audio',
                'codecs': [{
                    'name': 'OPUS',
                    'mimeType': 'audio/OPUS',
                    'clockRate': 48000,
                    'payloadType': int(line.split(' ')[-1]),
                    'channels': 2,
                    'rtcpFeedback': [],
                    'parameters': {
                        'useinbandfec': 1,
                        'sprop-stereo': 1
                    }
                }],
                'headerExtensions': [],
                'encodings': [{ 'ssrc': '' }],
                'mid': None,
            }
            section = mediasoupConfig['audio']
            encoding = mediasoupConfig['audio']['encodings'][0]
        elif line.startswith('a=rtpmap'):
            pt, codec = line.replace('a=rtpmap', '').split(' ')
            if section['kind'] == 'video':
                codec, clockRate = codec.split('/')
                section['codecs'][0]['name'] = codec.upper()
                section['codecs'][0]['mimeType'] = 'video/' + codec.upper()
                section['codecs'][0]['clockRate'] = int(clockRate)
                section['codecs'][0]['parameters'] = {
                    'vp8': None,
                    'vp9': None,
                    'h264': {
                        'packetization-mode': 1,
                        'profile-level-id': '42e01f',
                        'level-asymmetry-allowed': 1,
                    },
                    'h265': None,
                }[codec.lower()]
            elif section['kind'] == 'audio':
                codec, clockRate, channels = codec.split('/')
                section['codecs'][0]['name'] = codec.upper()
                section['codecs'][0]['mimeType'] = 'audio/' + codec.upper()
                section['codecs'][0]['clockRate'] = int(clockRate)
                section['codecs'][0]['channels'] = int(channels)
        elif line.startswith('a=framerate:'):
            section['framerate'] = int(line.replace('a=framerate:', ''))
        elif line.startswith('a=ssrc:'):
            ssrc = int(line.replace('a=ssrc:', '').split(' ')[0])
            encoding['ssrc'] = ssrc
        elif line.startswith('a=mid:'):
            section['mid'] = line.replace('a=mid:', '')
        elif line.startswith('a=rtcp-fb:'):
            pt, fb = line.replace('a=rtcp-fb:', '').split(' ', 1)
            fb = fb.split(' ', 1)
            type_ = fb[0]
            parameter = len(fb) > 1 and fb[1] or ''
            #try:
            #    parameter = int(parameter)
            #except ValueError:
            #    pass
            section['codecs'][0]['rtcpFeedback'].append({ 
                'type': type_, 
                'parameter': parameter
            })
        elif line.startswith('a=extmap:'):
            id, uri = line.replace('a=extmap:', '').split(' ')
            section['codecs'][0]['headerExtensions'].append({ 
                'uri': uri, 
                'id': id
            })
        #elif line.startswith('a=fmtp:'):
        #    pt, params = line.replace('a=fmtp:', '').split(' ')
        #    params = params.split(';')
        #    for param in params:
        #        name, value = param.split('=', 1)
        #        if section['kind'] == 'video' and name in ('packetization-mode', 'profile-level-id'):
        #            section['codecs'][0]['parameters'][name] = value
        #        elif section['kind'] == 'audio' and name in ('useinbandfec', 'sprop-stereo'):
        #            section['codecs'][0]['parameters'][name] = value
    #
    return mediasoupConfig


def mediasoupToSdp(config, transport, consumer=None):
    """
        Converts a MediaSoup transport/consumer object descriptors into an SDP 
        format used by GStreamer

        :param config: The configuration to use:
            {
              simulcast: false|true             # if simulcast should be enabled
              kind: 'video'|'audio'             # the media type
              codec: 'vp8'|'vp9'|'opus'|'h264'  # the media codec
              pt: Number                        # the payload type
            }
        :param transport: The MediaSoup transport 
        :param consumer: The MediaSoup consumer
        :return: the SDP string
    """
    sdpConfig = dict(
        iceLite = transport['iceParameters']['iceLite'] and 'a=ice-lite' or '',
        ufrag = transport['iceParameters']['usernameFragment'],
        pwd = transport['iceParameters']['password'],
        fingerprint_algorithm = transport['dtlsParameters']['fingerprints'][-1]['algorithm'],
        fingerprint_value = transport['dtlsParameters']['fingerprints'][-1]['value'],
        mid = '0',
        ssrc_lines = '',
        candidates = '\n'.join('a=candidate:%(type)scandidate 1 %(protocol)s %(priority)d %(ip)s %(port)d typ %(type)s' %candidate
            for candidate in transport['iceCandidates']) + '\na=end-of-candidates'
    )
    if consumer:
        ssrc = consumer['rtpParameters']['encodings'][0]['ssrc']
        cname = consumer['rtpParameters']['rtcp']['cname']
        sdpConfig['mid'] = consumer['rtpParameters']['mid']
        sdpConfig['ssrc_lines'] = '''\
a=ssrc:%(ssrc)s cname:%(cname)s
''' %dict(ssrc=ssrc, cname=cname)
    #
    sdp = '''\
v=0
o=mediasoup-client 10000 1 IN IP4 0.0.0.0
s=-
t=0 0
%(iceLite)s
a=fingerprint:%(fingerprint_algorithm)s %(fingerprint_value)s
a=msid-semantic: WMS *
''' %sdpConfig
    # add audio
    if config['kind'] == 'audio':
        sdpConfig['audio_codec'] = config.get('codec', 'opus').lower()
        sdp += '''\
a=group:BUNDLE %(mid)s
m=audio 7 UDP/TLS/RTP/SAVPF 100
c=IN IP4 127.0.0.1
a=rtpmap:100 %(audio_codec)s/48000/2
a=fmtp:100 useinbandfec=1;sprop-stereo=1
a=setup:active
a=mid:%(mid)s
a=sendrecv
a=ice-ufrag:%(ufrag)s
a=ice-pwd:%(pwd)s
%(candidates)s
a=ice-options:renomination
a=rtcp-mux
a=rtcp-rsize
%(ssrc_lines)s
''' %sdpConfig
    elif config['kind'] == 'video':
        sdpConfig['video_codec'] = config.get('codec', 'vp8').upper()
        sdpConfig['pt'] = config.get('pt', 101)
        if config.get('simulcast'):
            sdp += '''\
a=group:BUNDLE video1 video2 video3
m=video 7 UDP/TLS/RTP/SAVPF %(pt)d 106
c=IN IP4 127.0.0.1
a=rtpmap:%(pt)d %(video_codec)s/90000
a=rtpmap:106 rtx/90000
a=rtcp-fb:%(pt)d nack 
a=rtcp-fb:%(pt)d nack pli
a=setup:active
a=mid:video1
a=sendrecv
a=ice-ufrag:%(ufrag)s
a=ice-pwd:%(pwd)s
%(candidates)s
a=ice-options:renomination
a=rtcp-mux
a=rtcp-rsize
m=video 7 UDP/TLS/RTP/SAVPF %(pt)d 106
c=IN IP4 127.0.0.1
a=rtpmap:%(pt)d %(video_codec)s/90000
a=rtpmap:106 rtx/90000
a=rtcp-fb:%(pt)d nack 
a=rtcp-fb:%(pt)d nack pli
a=setup:active
a=mid:video2
a=sendrecv
a=ice-ufrag:%(ufrag)s
a=ice-pwd:%(pwd)s
%(candidates)s
a=ice-options:renomination
a=rtcp-mux
a=rtcp-rsize
m=video 7 UDP/TLS/RTP/SAVPF %(pt)d 106
c=IN IP4 127.0.0.1
a=rtpmap:%(pt)d %(video_codec)s/90000
a=rtpmap:106 rtx/90000
a=rtcp-fb:%(pt)d nack 
a=rtcp-fb:%(pt)d nack pli
a=setup:active
a=mid:video3
a=sendrecv
a=ice-ufrag:%(ufrag)s
a=ice-pwd:%(pwd)s
%(candidates)s
a=ice-options:renomination
a=rtcp-mux
a=rtcp-rsize
''' %sdpConfig
        else:
            sdp += '''\
a=group:BUNDLE %(mid)s
m=video 7 UDP/TLS/RTP/SAVPF 101 106
c=IN IP4 127.0.0.1
a=rtpmap:101 %(video_codec)s/90000
a=rtpmap:106 rtx/90000
a=rtcp-fb:101 nack 
a=rtcp-fb:101 nack pli
a=fmtp:106 apt=101
a=setup:active
a=mid:%(mid)s
a=sendrecv
a=ice-ufrag:%(ufrag)s
a=ice-pwd:%(pwd)s
%(candidates)s
a=ice-options:renomination
a=rtcp-mux
a=rtcp-rsize
%(ssrc_lines)s
''' %sdpConfig
    #
    return sdp