What decides the output sample rate? I ask for 48 kHz and get 44.1

[vdatanet 1640]

Emby 4.9.5.0, hitting the HTTP API directly with curl. I'm asking rather than reporting, because two routes behave differently and I suspect at least one of them is me holding it wrong.

Route 1 — /Audio/{Id}/stream.wav with AudioSampleRate=48000. The parameter clearly does something, but not what I asked for. From the transcode log, with a 96 kHz/24 FLAC as the source:

ffmpeg … -i "…/track.flac" -map 0:0 -vn -sn -c:a:0 pcm_s16le -ar:a:0 44100 -ac:a:0 2 …

Stream #0:0: Audio: flac, 96000 Hz, stereo, s32 (24 bit) ← input

Stream #0:0: Audio: pcm_s16le …, 44100 Hz, stereo, s16 ← output

 

I asked for 48000 and the server ran -ar 44100. So the value is read — something resamples — but what I sent isn't the target.

Route 2 — /Audio/{Id}/universal with MaxSampleRate=48000. Here it looks inert:

• 96 kHz source → AAC out at 96 kHz
• 192 kHz source → AAC out at 96 kHz
• adding EnableAutoStreamCopy=false changes nothing

Why 48 kHz specifically, given that 44.1 obviously plays fine. It isn't a preference: 48 kHz is the ceiling of the device I'm feeding, which won't take anything above it. From a 96 kHz source, 48 kHz is a clean 2:1 decimation; 44.1 kHz is a non-integer resample I didn't ask for and don't need — and the server pays for it in CPU on every track. On the /universal side the effect is different: the output rate follows the source, so a library with mixed rates changes rate from one track to the next.

Three questions, and any of them closes this for me:

1. On /stream, is AudioSampleRate meant as a target, or only as a trigger to resample — and what picks 44100?
2. Is that 44100 coming from a default device profile for an unknown client? I'm sending no DeviceProfile at all, so if that's the answer, I'll send one and stop asking.
3. On /universal, is there a parameter that caps the rate, or is that route by design "never resample"?

Happy to run any variation against my server and post the resulting ffmpeg line — that's how I got this one.

ffmpeg-transcode-dd0d84ff-2858-4207-8878-41d4056868a5_1.txt