Re: [Jack-Devel] VideoJACK

On Sun, August 21, 2011 15:51, Paul Davis wrote:
> On Sun, Aug 21, 2011 at 9:48 AM, Harry van Haaren <[hidden]>
> wrote:
>> Hey All,
>>
>> I wasn't aware that patches existed to route video around JACK...
>> although
>> the idea has been on list a couple of times before IIRC.
>> I'm aware the patches are pretty outdated at this stage, but if work was
>> to
>> be done in this area would mainline JACK versions be open
>> to taking it into upstream?
>
> this has been asked before, yes. the core developers of JACK (that
> includes me) were not happy with the specific way that the guys who
> did videojack went about it. we think that the general idea of video
> for jack is excellent. but the implementation would need to change in
> fairly fundamental ways for it be merged into any mainline version of
> JACK. i don't currently recall what the fundamental problems where.
> 
> Jack-Devel mailing list
> [hidden]
> http://lists.jackaudio.org/listinfo.cgi/jack-devel-jackaudio.org
>

Hi Harry,
I can probably answer this best, since I created the original (unofficial)
patch. There was a lot of discussion on this some time ago on this list,
and the conclusion was that only one major change would be needed to make
it compatible with jack. The change was to add a function
jack_set_video_process_callback(), which for now would simply be a wrapper
around jack_set_process_callback(). Then at some time in the future this
function could be reimplemented as as a new function which would use a
second clock within jack for the video timing.

However there were some other minor changes needed - in particular there
would need to be a new option to set the video clock rate (the patch just
uses -r to set the overall rate).

At the time of this discussion I was very busy with other work, and it was
about the time jack 1 was moving to (or being replaced by) jack 2, so I
did not have the opportunity to make the recommended change.

Anyway, the status is that the videojack patch works great for streaming
video, but it is based on what is now a very old version of jack. Another
drawback with the current patch is that you can only use the server for
either video or audio (due to the incompatible framerates).

What would be needed to make it current is for somebody to update the
patch to the most recent verion of jack 2, add an option to set the video
framerate, and create the jack_set_video_process_callback() as a wrapper
aroun jack_set_process_callback(). Then I believe the patch could be
worked into the main trunk of jack.


Anyway, if you want to try out the patch by all means go ahead. It does
work, but there are a couple of drawbacks as noted. I created sample in
and out clients for my project, LiVES, which you can see here:

http://lives.svn.sourceforge.net/viewvc/lives/trunk/lives-plugins/weed-plugins/gdk/vjack_rcv.c
(most of the code in here is to do with resizing the image, but look at
server_process and the init function)


http://lives.svn.sourceforge.net/viewvc/lives/trunk/lives-plugins/plugins/playback/video/vjack_output.c


Feel free to contact me on or off list if you need more info.


Regards,
Salsaman.

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