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87 lines
2.4 KiB
Markdown
87 lines
2.4 KiB
Markdown
---
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title: "Record Output Audio via Terminal"
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date: 2020-03-01T10:38:06-05:00
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draft: false
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tags: [ "Linux", "Audio-Video" ]
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---
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This post is specific to `PulseAudio` on Linux.
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I know of GUI based solutions like [PulseAudio Volume Control](https://freedesktop.org/software/pulseaudio/pavucontrol/) that lets you set up monitor devices. But, what if you want to do this through the terminal?
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Luckily, [b-ak](https://askubuntu.com/a/850174) on AskUbuntu gave an elegant answer to this question!
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First make sure you have `pulseaudio-utils` installed,
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```bash
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sudo apt install pulseaudio-utils
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```
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Next we need to search for the speaker we wish to monitor
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```bash
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pacmd list-sinks | grep -e 'name:' \
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-e 'index' \
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-e 'Speakers'
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```
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It will output something similar to this:
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```bash
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* index: 0
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name: <alsa_output.pci-0000_00_1b.0.analog-stereo>
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analog-output-speaker: Speakers (priority 10000, latency offset 0 usec, available: unknown)
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```
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From here note the name in `<>` of the speaker you wish to monitor. For example for my output above, I wish to monitor `alsa_output.pci-0000_00_1b.0.analog-stereo`.
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Next we will use the `parec` command to record the raw audio stream from the PulseAudio server.
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```bash
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parec --device alsa_output.pci-0000_00_1b.0.analog-stereo.monitor | encoder_command
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```
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Notice the addition of `.monitor` at the end of the device.
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## `lame`
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For the `encoder_command`, b-ak used `lame`.
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```bash
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lame -r -V0 - out.mp3
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```
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This command takes in a raw pcm `-r` and enables variable bit rates for the highest quality `-V0`. From there it encodes it and puts it in `out.mp3`.
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Now `lame` actually makes a couple assumptions about your raw pcm if you didn't specify additional arguments:
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- The Raw PCM is formatted in signed 16-bit little endian samples
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- The Raw PCM has 2 channels
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If you're assumptions don't meet the above, then you will need to add additional arguments.
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## `ffmpeg`
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We can replace `lame` with the more featureful `ffmpeg` if we take note of the same assumptions above.
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```bash
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ffmpeg -f s16le \
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-ac 2 \
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-i pipe:0 \
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-b:a 0 \
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out.mp3
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```
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Where we can replace the `.mp3` with whatever file extension `ffmpeg` supports.
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Now to show the entire command
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```bash
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parec --device alsa_output.pci-0000_00_1b.0.analog-stereo.monitor | \
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ffmpeg -f s16le \
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-ac 2 \
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-i pipe:0 \
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-b:a 0 \
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out.mp3
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```
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