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Heya! This is a pretty interesting and niche problem, but I’ll try to break it down and offer some suggestions.
Understanding the Audio Subsystem
Since your car’s media unit is running Linux, the first step is to figure out how the audio system is configured. Here’s how you can approach it:
-
Check for Audio Devices:
- Run
ls /dev/snd
to see if there are any ALSA (Advanced Linux Sound Architecture) devices. If you see files likepcmC0D0c
(capture) orpcmC0D0p
(playback), that’s a good sign. - Alternatively, run
aplay -l
orarecord -l
to list playback and capture devices, respectively.
- Run
-
Check for PulseAudio or PipeWire:
- Run
pactl info
to see if PulseAudio is running. - Run
pw-cli list-objects
to check for PipeWire (a newer audio server).
- Run
-
Check Kernel Logs:
- Run
dmesg | grep -i audio
to see if the kernel has logged any audio-related devices or errors.
- Run
-
Check for ALSA Mixer:
- Run
alsamixer
to see if you can interact with the audio mixer. This might give you insight into available channels.
- Run
Recording All Audio Channels
If you’re unsure which audio channels are active, you can try to capture all possible channels using ffmpeg
or arecord
. Here’s how:
-
Using
arecord
:- Run
arecord -l
to list available capture devices. - Use
arecord -D hw:0,0 -f cd -c 2 -t wav output.wav
to record from the first device (adjusthw:0,0
based on your device list).
- Run
-
Using
ffmpeg
:- Run
ffmpeg -f alsa -i hw:0 -ac 2 output.wav
to record from the first ALSA device. - If you suspect multiple channels, you can try increasing the channel count (e.g.,
-ac 6
for 5.1 surround sound).
- Run
-
Capture All Channels:
- If you want to capture all possible channels, you might need to experiment with the channel count (
-ac
) and device ID (hw:X,Y
). For example:ffmpeg -f alsa -i hw:0 -ac 8 output.wav
- This assumes your device supports up to 8 channels. Adjust as needed.
- If you want to capture all possible channels, you might need to experiment with the channel count (
Finding the Right Output
Since you mentioned wanting to feed the audio to a USB card, you’ll need to identify the correct audio output. Here’s how:
-
Check USB Audio Devices:
- Plug in your USB audio card and run
lsusb
to see if it’s recognized. - Run
aplay -l
orarecord -l
to see if the USB card appears as an audio device.
- Plug in your USB audio card and run
-
Route Audio to USB:
- Once you’ve identified the USB card, you can use
ffmpeg
orarecord
to capture audio and pipe it to the USB device. For example:ffmpeg -f alsa -i hw:0 -f alsa hw:1
- Here,
hw:0
is the source (your car’s audio system) andhw:1
is the USB card.
- Once you’ve identified the USB card, you can use
Debugging Tips
- Check Permissions: Ensure you have the necessary permissions to access audio devices. You might need to run commands with
sudo
. - Experiment with Channels: If you’re not getting useful audio, try different channel counts or devices.
- Look for Documentation: If you can identify the media unit’s manufacturer or model, there might be documentation or forums with more specific info.
Long-Term Solution
If you’re planning to keep this setup long-term, consider writing a script to automate the audio capture and routing. You could also explore using pavucontrol
(PulseAudio Volume Control) or qpwgraph
(PipeWire Graph) to manage audio routing more easily.
Good luck, and let me know how it goes! 🚗🎶