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

Kevin Layer layer at franz.com
Fri Nov 21 02:33:43 CET 2014


Dan Pascu wrote:

>> 
>> 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.

OK, fair enough.  And, I'm not an expert.  I'll will point out it used
to work fine, though.  I've used Blink daily (at home and work) for >
6 months, and this is a new problem, with no changes to the Asterisk
side.  (We installed from source and don't use any automatically
updating yum repo.  We're on CentOS 6.5.)

>> 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.

It's definitely an audio call.  What I see is an "Accept" button.  I
don't see two, one for accepting audio and one for video.  In fact,
the title of the window is "Audio call for ..." (or something like
that, but it definitely had `audio' in it).

So, to recap, I don't see "Audio only" anywhere.  I did look in
Blink's Preferences and I did uncheck all the boxes I saw there.  That
didn't change the observed behavior (server failure).

>> > 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.

Well, maybe I'm misunderstanding something, but I don't see that.  I'm
on a Macbook but I have the lid closed and I'm using an external
keyboard, mouse and monitor.  So, the camera is probably in some
disabled state.

At home, I'm on a Mac that does not have a camera, but I get the same
behavior there.

>> > 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.

I don't have enough experience in this area to even have an opinion
about Asterisk's worthiness or reliability.  We have used it for years
here at work, and I've used it for at least 3 years at home.  Never
had any problems at all.

What do you consider to be a better SIP implementation, on the server
side?

>> 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:
>> 
>> [default]
>> videosupport=no

It is under my control.  And thanks for the suggestion.  I just found
this after my last email.  We use Freepbx on top of Asterisk, and I
did find an option in the web interface to turn off video, server
wide:

  Settings -> Asterisk SIP Settings, Video Support: Enabled -> Disabled

In fact, it has allowed me to accept audio calls again.

This seems like a blunt instrument, though.  If others want to do
video calls, I've just stopped them from doing so, just because Blink
changed to not handle something it's handled for a long time.  As I
said, our Asterisk hasn't changed in a long time.  We use version
1.8.11, which is 2.5 years old, btw.

Dan, I appreciate you taking the time to respond.  Thank you.

Kevin


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