hello,
The open GL rendering is made in the GPU. grabbing the images by the CPU in 
order to compress them and to record them in the HDD is a slow operation.
I think some software are able to compress the image in the GPU in order to 
grab a smaller file, but Gem don't.
So, there is not a lot's of solution, and you already found them.

I use pix_record when I need a correct quality of a small video. I use mjpa 
with good result.

When I need better quality, I use pix_writer. Usually this can not be made in 
real time. I.E : I create a process that render exactly what I want, without 
human interaction. (For live performance, I record all human interaction in 
tables or texts file during the performance, then I use this data to play again 
the same performance)
Then, It's possible to record both image annd sound in the same time. Even if pd will not 
be sync with real (external) time, the time inside pd will still stay consistent. I.E : 
even if there are lot's of audio dropout and the recording fps is 1/2 of the real fps, pd 
will still record a perfect audio file that will be perfectly sync with the video. You 
just need to start the audio and video recording with the same "bang".


cheers
Cyrille

Le 28/05/2020 à 22:33, ffdd cchh a écrit :
Hi everyone,

Is it possible to grab the OpenGL stream with ffmpeg and save to a video file? 
If so, could anyone point in the right direction as to how to capture the 
stream opened by Gem?

The reason I ask this is that I am looking for ways to render video frames to a 
file and I have not managed a good result using neither [pix_record] nor 
[pix_writer].

With [pix_record] I have systematically tried all codecs and colorspaces and I 
had no luck.

With [pix_writer], I did manage high quality frames with the correct colorspace 
which I then concatenated into a video (with ffmpeg). The drawback I have with 
[pix_writer] is the time it takes to write, which really complicates audio and 
video synching.

Thanks!!

Fede
--
fdch.github.io <http://fdch.github.io>

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