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Comment by arp242 | Hacker News Reader

> If your Linux laptop doubles as a music player, another nice new feature is that you can now stream your audio over USB even while the rest of your system is asleep. That capability's been available in Android for a while, but now it's part of mainline Linux.

How does that work? You still need some program to actually play the music (mpv, Sotify, whatnot)? Or what am I misunderstanding? Unfortunately there are no details in the article, and an interwebz search doesn't really show anything.

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It's probably related to this:

https://www.phoronix.com/news/Linux-6.16-QCOM-USB-Audio-OLOA...

Audio usb offloading. Only supported on Qualcomm soc's.

Article is misleading. Audio offloading is probably only useful to avoid waking the main CPU too often, so better battery management... CPU can remain sleeping a few microseconds longer, not all the time.

Not something many will benefit.

A 20 MB 3.5 minute .flac file takes ~200 ms to decode into a 35 MB .wav on my desktop, so in principle the program could spend a small fraction of a second placing the decoded audio into a small buffer and give a pointer to hardware to keep playing it while the rest of the system goes to sleep for a few minutes. Or if the hardware has direct support for the codec, it could just give it the file as-is.

Since pulseaudio defaults to software mixing, this huge buffer would just get gradually copied to the actual kernel playback buffer one 25ms chunk at a time..

I believe even Debian defaults to PipeWire instead of PulseAudio, so I doubt there are many systems left using PA.

It probably requires active standby/s0ix. Modern Intel chips actually don't officially support s3 at all anymore, only s0ix.

The whole point is to support stuff like this

Maybe it’s using Wake-on-LAN where the network interface is alive while the rest of the system is dormant? Perhaps the music stream is encoded in magic packets?

I found [1], which says "For Qualcomm hardware where the USB audio can be offloaded to a dedicated audio DSP for handling the transfers to the USB host controller, this lessens the work of the main CPU cores and can help with power management so those CPU cores can hit lower power states or tackle other work. Other hardware vendors will hopefully follow suit in their support for the upstream support around USB audio offloading."

So I think that it doesn't do anything for the average Linux laptop, and is mostly intended for certain (mobile) hardware?

[1]: https://www.phoronix.com/news/Linux-6.16-USB-Audio-Offload

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