Keith, I am not quite sure how to answer this. I do not really
understand what you need and are asking for. It does not sound like
there are many MLT applications that are close to what you need. With
Shotcut or melt, you can record (capture and encode) from HDMI, SDI,
and V4L. If you use FireWire cams, MLT can receive the stream through
libavdevice as long as there is no stream discontinuity, but it can
only then decode it and then do something else with it like view or
encode to file. In other words, it does not provide direct capture to
file of FireWire data streams like dvgrab does.
Thanks for your reply, Dan. It looks like the best approach might be to use
dvgrab for the capturing side of things, then a mixture of custom and existing
MLT tools to do the rest. It doesn't matter if it's a bit of a cobble-together
at this stage. Can MLT handle HDV clips captured by dvgrab, then? Essentially,
the most important thing I want to do is to be able to create an app that play
two files simultaneously in sync (while they are still being captured by dvgrab
or whatever), and log points where we want to switch from one source to the
other. That logged information can then be used to create a compiled video
using existing tools.
MLT can switch between sources and clips. Shotcut shows this can be
done by letting you add live sources to a playlist alongside clips.
However, there is no MLT app I know of that shows more than one device
source in a multiview while simultaneously capturing let alone
switching between them. Developing something for this will take a lot
of time if you do not already know MLT.As long as we have some kind of
methodology that gets the job done in a fashion to start with we've got 5
years of this contract to tinker with it and get it right. We did something
similar last year, but were simply recording to SD cards in the cameras and
then clipping this material up with existing tools (KDenLive, mainly). What
I'm trying to do is find tools like dvgrab and MLT that might help us
streamline the process.
With that said, here is a python script that comes with MLT that
provides a very simple web service that switches between two sources,
outputting to a third:
https://github.com/mltframework/mlt/blob/master/src/swig/python/switcher.py
You can execute this to see what it does without DeckLink devices:
./switcher.py color:blue noise: sdl
Then "curl localhost:8888/switch" to trigger it. It does not actually
do a simple switch; rather, a friend needed it to reduce input 1 size
by 20% revealing input 2 in the background along the left and bottom
edges, and then to return input 1 to full size on the next switch.
Sounds interesting. I just need to look at examples like this to see what can
be done.
I am afraid I will not be able to help you much with the project as
this is just a part time hobby, and I am already so busy with Shotcut.
Understood. I'm happy to do the donkey work myself, and it's great that there
are open-source projects around which I can study.
Do you know about DVswitch? http://dvswitch.alioth.debian.org/wiki/
Alas, that appears to be a SD only solution.
Also, from this list:
http://www.opensourcebroadcast.com/category/directory/video-post-production
Snowmix and Open Playout are 2 gstreamer-based projects worth considering.
Again, interesting. These are all tools which might prove useful. As I said,
it doesn't matter if I have to cobble together several different tools at this
stage. We can worry about something more refined and better integrated later.
Regards,
Keith
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