Streaming Music

Streaming Methods

Koel supports three streaming methods which can be configured via the STREAMING_METHOD setting in .env file:

php: Uses native PHP file reading. This is the default method.
x-accel-redirect: Only applicable if your webserver is nginx. Uses nginx's X-Accel module, designed for serving larger contents directly to the end user. Refer to nginx.conf.example for a sample nginx configuration file.
x-sendfile: Only applicable if your webserver is Apache (with or without a proxy server like nginx). Uses Apache's mod_xsendfile module. You'll need to install and configure the module manually. A sample configuration is as follows:
apache
```
LoadModule xsendfile_module   libexec/apache2/mod_xsendfile.so

# These configuration can be put in the VirtualHost directive as well
<IfModule mod_xsendfile.c>
  XSendFile on
  XSendFilePath /mnt/media
</IfModule>
```
Note that although its home page denotes "Apache2/Apache2.2," the module itself is known to work with later versions of Apache as well.

When streaming from a cloud storage like S3 or Dropbox, Koel will simply use the presigned URL provided by the storage service. A pre-signed URL is a secret, generated on-the-fly URL that provides temporary access to your (private) files stored in the cloud. Koel sets the expiration time of these URLs to 1 hour.

Lossless Transcoding

Koel supports transcoding your lossless audio to AAC, a format widely supported by modern browsers. To enable this feature, you'll need to have FFmpeg installed on your server and set its executable path via the FFMPEG_PATH setting in the .env file. If you use the Docker image, this is already done for you.

The transcode quality can be controlled via TRANSCODE_BIT_RATE. The default value is 128, which means the audio will be transcoded to 128 kbps AAC. You can set it to a higher value, such as 192, to improve the audio quality at the cost of a larger file size. Practically, it's almost impossible to differentiate between 320 kbps AAC and lossless audio.

As transcoding can take some time (albeit typically several seconds) and resources, Koel will cache the transcoded files for later use. You should also expect a slight delay when you first play a song that requires transcoding, as Koel will need to do its transcoding magic first (which can involve downloading the file from your cloud storage if necessary).

FLAC Transcoding

Since FLAC is well-supported by modern browsers, Koel streams FLAC files as-is by default and maintains the lossless experience. You can also force transcoding FLAC as well by setting TRANSCODE_FLAC to true in the .env file.

Forced Transcoding

For audio formats that aren't widely supported by browsers, such as AIFF or APE, Koel will always resort to transcoding. If you upload files in such formats, make sure the FFmpeg setup and configuration (see above) are correct.

Transcoding on Mobile

On a mobile device where data usage is a concern, the user might want to instruct Koel to transcode all songs (regardless of their formats) to a lower bit rate to save bandwidth. This can be done via the Preferences screen.

Crossfade

Koel supports crossfading between songs, where the currently playing track fades out while the next track fades in, creating a seamless transition. The crossfade duration can be configured from 0 to 15 seconds via the Preferences screen. A value of 0 disables crossfade.

:::tip Crossfade is automatically skipped for tracks shorter than twice the crossfade duration, and is not applied when the repeat mode is set to "Repeat One" or during radio playback. :::