docs(playout): add a tutorial to enable AAC in liquidsoap (stable-4.x) (#2909)

Backport b6c3ece7d9 from #2904.

BEGIN_COMMIT_OVERRIDE
docs(playout): add a tutorial to enable AAC in liquidsoap
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---------

Co-authored-by: Thomas Göttgens <tgoettgens@gmail.com>
Co-authored-by: Kyle Robbertze <kyle@paddatrapper.com>

docs/admin-manual/stream-configuration.md

@@ -17,6 +17,12 @@ Setting a higher bitrate for your output stream will only benefit your listeners
 
 :::
 
+:::caution
+
+The liquidsoap playout handler version 1.4.3 shipped in Debian Bullseye and 1.4.1 shipped in Ubuntu Focal doesn't support AAC streaming output. If you want to stream AAC, you will need to replace the liquidsoap package with a version that supports AAC. See this [tutorial](./tutorials/setup-liquidsoap-aac-streaming.md) for more information.
+
+:::
+
 ## Icecast
 
 ### UTF-8 metadata in Icecast MP3 streams

docs/admin-manual/tutorials/setup-liquidsoap-aac-streaming.md

@@ -0,0 +1,54 @@
+---
+title: How to update liquidsoap to support AAC streaming
+---
+
+This tutorials walks you though the steps required to replace the liquidsoap package with a version that supports AAC streaming.
+
+:::warning
+
+Replacing the liquidsoap package has security implications, since this will remove the package from the system's package manager. This means that the package manager will not be able to update the liquidsoap package in the future. This includes backports of security fixes.
+
+Libretime is NOT compatible with Liquidsoap 2.x at the time of this writing. Future versions of Libretime will support Liquidsoap 2.x which will render these instructions obsolete.
+
+:::info
+
+Lets assume you already [installed LibreTime using the native OS installer](../install/install-using-the-installer.md). Execute the following commands as the libretime user.
+
+:::
+
+## 1. Obtain liquidsoap with AAC support
+
+For Ubuntu 20.04 LTS ('focal'), use the following file:
+
+```bash
+wget https://github.com/savonet/liquidsoap/releases/download/v1.4.4/liquidsoap-v1.4.4_1.4.4-ubuntu-focal-amd64-1_amd64.deb
+```
+
+For Debian 11 ('Bullseye'), use the following file:
+
+```bash
+wget https://github.com/savonet/liquidsoap/releases/download/v1.4.4/liquidsoap-v1.4.4_1.4.4-debian-stable-amd64-1_amd64.deb
+```
+
+## 2. Install and replace the liquidsoap package
+
+Install the package using `apt`, then remove the old liquidsoap dependencies:
+
+```bash
+sudo apt -y install ./liquidsoap-v1.4.4_1.4.4-*-amd64-1_amd64.deb
+sudo apt -y autoremove
+```
+
+## 3. Configure LibreTime to use the new liquidsoap package
+
+Nothing to do, this is a drop-in replacement. Just restart the libretime target once and then check the status page in the LibreTime web interface to see if the liquidsoap service is running.
+
+```bash
+sudo systemctl restart libretime.target
+```
+
+:::warning
+
+If you want to update LibreTime in the future, you'll need to re-run the installer schript. This will replace the liquidsoap package with the version that doesn't support AAC streaming. Add `--packages-excludes liquidsoap` to the installer command to prevent this from happening.
+
+:::