[mythtv-users] USB vendor=534d device=2109

[Will Dormann]

On 7/29/20 7:02 PM, Will Dormann wrote:

> If you're fine with stereo sound, then you might be good to go with a
> setup such as the above.  And to be honest, despite the output file from
> obs having 5.1 channels, I'm not completely certain that it's not just
> faking it.  The obs documentation states that "There is an automatic
> channel rematrixing when either downmixing or upmixing is mandated by a
> difference in channel layouts between source and output."   So it's
> possible that the LFE channel was just logically produced based off of
> the stereo input by obs.



For what it's worth, I've confirmed (with a 5.1 speaker test video file)
that obs is indeed faking it by upmixing.  Here's a very-recent Linux
kernel patch that makes the audio stereo (as opposed to mono) from this
device (which is apparently a MacroSilicon MS2109 it seems):
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e337bf19f6af38d5c3fa6d06cd594e0f890ca1ac

So if you're on a Windows or OSX system, or a Linux device with a kernel
that's about 2 weeks old or older, you can probably only ever expect to
get mono audio out of this device.  If you've got a very recent Linux
kernel, you might be able to get stereo.  With yesterday's 5.8.0 kernel,
I have confirmed that the audio coming from the MS2109 is indeed stereo.
 But the left and right channels are swapped (as the above kernel commit
suggests), and there seems to be some other bug that prevents any
/dev/video* device from appearing when the device is plugged in.
<https://bugs.archlinux.org/task/67460>
In my testing, removing the virtual sound card device from my VM allows
it to capture video and swapped-stereo sound.

So yeah, it seems not quite ready for prime time.  But given the
appropriate efforts spent, it could potentially be viable as a
super-cheap HDMI video capture device.



-WD