Mono tracks, transcoding and AI

[MarmiteSandwich]

(31-10-2026 10:59)MarmiteSandwich Wrote:  Any suggestions welcome.

Well, I consulted Claude. I hope there are no rules about this with the forum.
This was the answer and it worked immediately:-

Quote:Replace "convOut=-af volume=replaygain=track" with "convOut=-af volume=replaygain=track -ac 2"

Apparently,

Quote:What’s likely happening

Double speed with a pitch about an octave up is the classic signature of mono samples being read as stereo. ffmpeg outputs a 1-channel WAV, but something downstream (BubbleUPnP Server or the WiiM) treats it as 2-channel. It then consumes each pair of consecutive mono samples as one L/R frame, so the audio plays at twice the speed and finishes in half the time. Stereo files never hit this, which fits your symptoms.

Fix to try first: force stereo output

Add -ac 2 to the convOut so ffmpeg upmixes mono to dual-mono:

Hope someone else finds this useful. It does tend to raise interesting questions about how we all use forums and how they will develop in the age of AI.

Anyway, problem solved.
Cheers,
Marmite.
PS this was a free Claude account, not a subscription.