Video with alpha to file

[amindfv at mailbox.org]

I've got an A420_10LE video stream I'd like to write to a file, preserving its alpha channel.

I've found that I can use ProRes, with a pipeline like:

    ... ! video/x-raw,format=A420_10LE ! videoconvert ! video/x-raw,format=A444_10LE ! avenc_prores ! qtmux ! filesink

This works but it's slow and results in massive files (almost 5GB for 30 seconds of 1080p video).

Are there faster+smaller options (encoders and maybe muxers) for writing to files with alpha? And in the spirit of learning to fish, how could I have found them (e.g. with `gst-inspect`)?

Thanks,
Tom