[asterisk-dev] extend IAX2 IE proposal

[Russell Bryant]

Tilghman Lesher wrote:
>> Doesn't IAX2 support transfer of images (GIF, JPG, etc)?  If so, how
>> is that handled?
> 
> They're encoded in mini-frames, as part of the media exchange, not in
> full frames.

Well, that's not completely true.  There are a couple different ways this is 
handled.

The first is for a call which is exchanging video.  These video frames are sent 
in meta video frames (slightly different encoding than mini frames).  However, a 
full frame of type VIDEO must be sent every 65536 ms due to re-sync the 
timestamps due to wraparound.  This is because voice mini frames and video meta 
frames carry a 16-bit timestamp, while the full timestamp is 32-bits, and is 
only sent in full frames.

Also, there is an IMAGE full frame type which is used to send a single image 
within an existing call.  If anyone ever used gnophone and remember how it would 
send a single picture of you to the other party in the call, this is how the 
image would be sent.

-- 
Russell Bryant
Software Engineer
Digium, Inc.
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