Forced opus transcoding and audio loop when casting

Plex Labs
,
1

Server Version#: 1.42.2.10156
Player Version#: 4.157.0

Hi,

I’m encountering a strange playback issue when casting FLAC music from Plexamp/Plex Web to a JBL Authentics 200 (Google Cast) using my Plex Media Server running on a NUC (Docker — Linuxserver image).
On some FLAC tracks (always the same ones), playback starts normally, but after ~4–5 seconds the last second of audio starts looping indefinitely.

This issue only happens in the following scenario:

  • Source: Plexamp/Plex Web
  • Server: Plex on NUC via Docker
  • Output: Cast to JBL speaker
  • Playback mode: audio transcoded to OPUS (not by choice)

Tests performed

Playing the same FLAC track on Nvidia Shield
→ Direct Play FLAC — works fine
Casting the same FLAC file via VLC to the JBL speaker
→ Works fine
Casting via Plexamp → OPUS transcoding
→ Audio loops after ~5 seconds
Casting via Plexamp → Server transcodes to MP3 (custom profile - Chromecast.xml)
→ Works fine

All tracks are from the same album, same encoding (16-bit / 44.1 kHz FLAC).
Only certain tracks exhibit this behavior.
Relevant log extract from the failing playback
The session is always started as a transcoded stream, even though the Chromecast profile already declares FLAC as Direct Play compatible:

/music/:/transcode/universal/start
directPlay=0
directStreamAudio=1
audioCodec=opus

The server then forces OPUS transcoding:
codec:0 libopus -b:0 512k -segment_time 1

Example file properties:

02 - The Walkabout Bounce.flac
Sample rate: 44100 Hz
Channels: 2
Bit depth: 16
Codec: FLAC

What appears to be happening
Chromecast Audio never receives FLAC as Direct Play
even though the profile already contains:
<MusicProfile container="flac" codec="flac"/>

Plexamp always initiates playback with directPlay=0
which forces the server into the universal transcoder pipeline default audio transcode target = OPUS 48 kHz

With some FLAC files:
playback runs fine for ~5 seconds
then the output loops the last second indefinitely

When modifying the Chromecast profile to force music transcoding to MP3 instead of OPUS:
Playback works
But quality is reduced (no longer lossless)

This strongly suggests the issue is related to:
OPUS transcoding + Chromecast Audio / JBL Cast
triggered only with certain FLAC tracks

**Questions
**

  • Is this a known issue in the OPUS transcoding pipeline for Cast audio?

  • Why does Plex never attempt Direct Play FLAC to Chromecast Audio, even when the device appears capable of handling it?

  • Is there a recommended workaround to allow FLAC Direct Play for Cast audio ?

Thanks a lot for any help !

Chrisbati