sipsorcery's blog

Occassional posts about VoIP, SIP, WebRTC and Bitcoin. response times SIP Sorcery Last 3 Hours
daily weekly status

Building a video softphone part IV

I haven’t made much progress since the last post except to determine that I was barking up the wrong tree by attempting to combine an the audio and video streams with the media foundation. I decided to check the RTP RFCs related to H.263 and H.264 to determine how the audio and video combination should be transmitted and it turns out they are pretty much independent. That means to start with I can use the existing softphone code for the audio side of things and use the Media Foundation to do the video encoding and decoding. I’m thinking of switching to H.263 for the first video encoding mechanism as it’s simpler than H.264 and will be easier to package up into RTP.

For the moment I will keep going with my attempt to get the Media Foundation to save a video and audio stream into a single .mp4 file as I think that will be a very useful piece of code to have around. The problem I’m having at the moment is getting the audio encoding working. The audio device I’m using returns a WAVE_FORMAT_IEEE_FLOAT stream but from what I can determine I need to convert it to something like MFAudioFormat_Dolby_AC3_SPDIF MFAudioFormat_AAC for MPEG4. I need to investigate that some more.

One added benefit of looking into how RTP transmits the audio and video streams is that I finally got around to getting a video call working between my desktop Bria softphone and the iPhone Bria version. I’ve never had much luck with video calls between Bria softphones in the past, the video would get through sporadically but not very reliably. So I was pleasantly surprised when with a few tweaks of the NAT settings on the iPhone version I was able to get a call working reliably. Although it’s still not quite perfect as the video streams will only work if the desktop softphone calls the iPhone softphone and not the other way around. Still it’s nice to see video calls supported through the SIPSorcery server with absolutely no server configuration required. That’s the advantage of a SIP server deployment with no media proxying or transcoding.