[Telepathy] Problem for video call

[flower bean]

Hi,
I try to use Telepathy-qt4 API to implement video call with GTALK protocal.
I called below API in my demo:
   QStringList clientCapabilities;
        clientCapabilities
            <<
QLatin1String(TELEPATHY_INTERFACE_CHANNEL_INTERFACE_MEDIA_SIGNALLING
"/gtalk-p2p")
            <<
QLatin1String(TELEPATHY_INTERFACE_CHANNEL_INTERFACE_MEDIA_SIGNALLING
"/ice-udp")
            <<
QLatin1String(TELEPATHY_INTERFACE_CHANNEL_INTERFACE_MEDIA_SIGNALLING
"/wlm-8.5")
            <<
QLatin1String(TELEPATHY_INTERFACE_CHANNEL_INTERFACE_MEDIA_SIGNALLING
"/video/h264")
            <<
QLatin1String(TELEPATHY_INTERFACE_CHANNEL_INTERFACE_MEDIA_SIGNALLING
"/video/theora")
            <<
QLatin1String(TELEPATHY_INTERFACE_CHANNEL_INTERFACE_MEDIA_SIGNALLING
"/audio/speex");
    ensureStreamedMediaCall( contactName, userActionTime,preferredHandler )
);
    QList<Tp::MediaStreamType> request_types;
    request_types.append(Tp::MediaStreamTypeVideo);
    request_types.append(Tp::MediaStreamTypeAudio);
   ret = (*mWaiter)( mChannel->requestStreams( aTarget, request_types);

Error log as below:
  DEBUG: Received StreamedMedia.StreamError for stream 1
  with error code 2 and message: ""
Error code:
Codec negotiation failed

I'm not sure if I need call some codec API and if I need to launch camera by
myself, has telepathy packaged them and there are Available API already?

Thanks,
Cassie
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