Conversion

Each library has Conversion rules under Settings → Library. They say what a download becomes before it is verified, tagged and filed. There is one rule for each kind of source:

Rule	Applies to	Default
YouTube downloads	YouTube’s Opus audio	AAC, 256 kbps constant bitrate
Lossy files (MP3, AAC, Opus, Vorbis…)	Lossy files from any other source	Keep as downloaded
Lossless files (FLAC, ALAC, WAV…)	Lossless files from any other source	Keep as downloaded

The options

Each rule has an Action: Keep as downloaded, AAC (.m4a), MP3 or Opus. The lossless rule also offers FLAC and ALAC (.m4a). When the action converts, you also choose:

• Mode: Constant bitrate, or for MP3 only LAME quality (VBR) (V0 best to V9 smallest).
• Bitrate: 128, 160, 192, 256 or 320 kbps.
• Sample rate: keep the source’s, 44100 Hz or 48000 Hz.
• Container: .opus or .ogg, for Opus targets and for a kept YouTube file. A YouTube Opus file kept as .ogg is only renamed.

The rules that cannot be changed

• Never lossless from lossy. FLAC and ALAC are only offered for lossless sources, and a lossless target for a lossy file is refused.
• Never .webm.
• A file already in the target codec is kept as it is and not re-encoded.
• A converted file keeps the quality it was downloaded at. A FLAC converted to MP3 320 still counts as FLAC; a YouTube file turned into AAC still counts as OPUS-160. Otherwise a library that converts FLAC to MP3 would search for a FLAC upgrade forever. The song shows both what was downloaded and what is on disk.

Convert files you already have

• A whole library: Convert existing files… on the library’s settings tab. It plans the conversion first: how many files change, the current size and the estimated size, and what each file goes from and to, with the reason for any that are skipped. Press Convert to run it.
• One song: Convert… in the song’s actions menu on the Library page. Choose a one-off rule, or use the library’s rules.

Files are converted one at a time. The new file is checked (it decodes, and its length is within 1 second of the original), tagged and filed under the naming template with its new extension. The original goes to the recycle bin, so you can get it back. A file that fails to convert stays where it was. A file in a reference library is never converted. The History records a “Converted” event, and Plex is asked to scan the folder.

ReplayGain

A library can write ReplayGain tags, so players (Plexamp, foobar2000, mpd, Navidrome and others) play songs from different sources at one loudness. Turn on Write ReplayGain tags on the library’s settings tab and press Save; it is off by default.

• Each file is measured with ffmpeg (EBU R128 loudness and true peak) and tagged REPLAYGAIN_TRACK_GAIN and REPLAYGAIN_TRACK_PEAK against ReplayGain 2.0’s −18 LUFS reference, in MP3, FLAC, M4A and Opus files alike. Only the tags change; the audio is never touched. No album gain is written.
• New imports are measured as they are filed, and a converted file is measured again.
• Measure existing files (shown on the library’s tab once the switch is on and saved) measures and tags the files already in the library, one song at a time. Files in a reference library are never re-tagged.
• With the switch off, the library’s files carry no ReplayGain tags: tags a file arrived with are replaced like every other tag.