[draft] USB Audio Support

[lqs]

This pull request introduces initial support for USB audio devices in JetKVM. With this feature, remote hosts can now select a USB audio output, and JetKVM will capture the audio stream from that device and transmit it to the web console for playback.

To set it up:

1. Build the audio module from https://github.com/lqs/jetkvm-audio

2. Copy the binary JetKVM device

Make sure the binary is placed at /userdata/jetkvm/bin/jetkvm_audio and is executable.

TODO

• Add a mute button to the web console
• Allow enabling/disabling the audio device
• Remove the FFmpeg dependency

It’s still rough, but I hope it can be a step toward better sound functionality.

[john--]

Very cool that you were able to accomplish this! Agreed, it's a little choppy. By any chance are you exhausting the resources of the hardware?
I use absolute mouse positioning and noticed cursor lag. Without audio (on the dev branch code) my cursor movement is instantaneous. Has anyone else noticed this?

[lqs]

Finally turned out that the RTP timestamps generated by FFmpeg were uneven and had incorrect intervals. Adjusted according to RFC7587 with a 960 increment per packet, resulting in perfectly smooth music playback.

@john-- Maybe the cursor lag is also caused by incorrect timestamps, which slow down the video to stay in sync with the audio.

[john--]

Finally turned out that the RTP timestamps generated by FFmpeg were uneven and had incorrect intervals. Adjusted according to RFC7587 with a 960 increment per packet, resulting in perfectly smooth music playback.

@john-- Maybe the cursor lag is also caused by incorrect timestamps, which slow down the video to stay in sync with the audio.

Interesting. It does seem a lot better now, nice work. The only thing I've noticed is that ffmpeg seems to use quite a lot CPU.

[adrianmeraz]

@lqs any word on when this can be merged in? Hope your PR doesn't stick around in limbo

[jeisom]

Would/Could it be have the option of a half rate audio? Say 22500 or 24000. Should be lower cpu usage and bandwidth if those are concerns. Would be good enough for basic remote management stuff.

[euforic]

Is it possible to make the device you are adding have audio out and audio in?

[pennycoders]

Hey guys! Any updates on this?

[adamshiervani]

Awesome work, and thanks for building the foundation, @lqs!

As the @pennycoders took this to the finishing line in #718, I will close this PR. Their PR is currently in review and tracked for the next release, 0.5.0.