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content/blog/recordoutputaudio.md

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