[Blink] New Blink Pro for OSX version 4.1.0 with ZRTP end-to-end audio/video encryption

Dan Pascu dan at ag-projects.com
Fri Nov 21 01:34:41 CET 2014

On 20 Nov 2014, at 20:54, Kevin Layer wrote:

> ag at ag-projects.com wrote:
>>> As Dan explained, the problem is not in Blink but in the remote
>>> server. The server should not send a video stream at all or if it
>>> sends one it must be syntactically correct. 
>>> I am not sure what we can fix in this respect but you should ask you
>>> provider to make a fix their server as their INVITE is broken.
> Counterpoint: Just because the video stream could not be negotiated
> does not mean that it must reject the invite entirely.  

Unfortunately things are not that simple as they seem at face value. It's a chicken and egg problem, because you need to decide early if you accept video or not and the error negotiating the codec happens later, by which time you cannot just go back on your decision and say I don't want video anymore.

Anyway, despite this, you are in full control of what you want to accept. I'm pretty sure this is not a video call, so why do you accept video anyway? Just press "Audio only" on the incoming call dialog and video will be refused and it will be like before video support was added. If it is a video call, then go to preferences and change your resolution from HD to VGA and then it should work when you accept video as well.

> How do they
> explain the successful operation of all of our other devices which
> work properly with this version of Asterisk?  Are they all out of
> spec?

Do those devices support video? If not, then obviously they refuse the video stream off the bat, which is something you can do as well as mentioned above.

> Further, rfc3984 (and the newer rfc6184) indicates that
> profile-level-id is an optional parameter.

And that is a mistake with the rfc. H264 cannot work unless both sides agree on the EXACT same parameters. If one side doesn't specify what they plan to use, I can only take a guess and most likely fail (which is exactly what you observe here). This is the reason why it'll probably work if you switch to VGA.

> And, it's not like we have some crazy, off-brand server.  We're using
> the LTS branch of Asterisk without modification.

Unfortunately asterisk is far from being a reference (or even reliable) SIP implementation by which everything else can be judged, despite it being popular. Adding a video stream to an audio only call is what I would call crazy.

If asterisk is under your control you might be able to configure it not to add a video stream to audio only calls. Not sure if there is a setting to make asterisk only add video if the caller asked for video, but if you do not need video at all, it can be disabled entirely:


> Kevin


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