[PD] [GEM] output gemwin to video file workaround using ffmpeg on macos

cyrille henry ch at chnry.net
Fri May 29 09:45:03 CEST 2020

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".


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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