Tightening Radarr quality profiles to stop Emby transcode lag

Avengers playback was crawling on Emby. Not network, not the client — the Synology CPU was pinned, fan howling, every play.

What was happening

The file that triggered it was a 42 GB REMUX of Avengers: Endgame, packaged as a Blu-ray 3D ISO. Two compounding issues:

The audio was DTS-HD MA 7.1 lossless. No consumer Emby client passes that through, so every play forced an ffmpeg audio transcode on the NAS.
The video was a 30+ Mbps source streaming over residential upload. Even when direct-play worked, it saturated the pipe.
The container was a BD ISO, so some clients refused to play it at all and the server had to parse disc structure first.

Other titles in the library had the same shape — REMUX MKVs at 30–40 Mbps, sometimes much larger. Anything Marvel hurt.

What I found

Radarr's "Any" profile and both 1080p profiles allowed Remux-1080p, Remux-2160p, and BR-DISK as valid grabs. Once those qualities entered the library, Emby was guaranteed to transcode every play to anyone not on a wired LAN client with a modern receiver. The real cap should have been Bluray-1080p x264/x265 — still great quality, but small enough to direct-play and use compressed audio.

The fix

Disabled the heavy qualities on the three affected profiles via the Radarr API:

# For each profile id (1, 4, 6), patch the qualities array to disable
# Remux-1080p, Remux-2160p, and BR-DISK while keeping Bluray-1080p enabled.
curl -X PUT "$RADARR/api/v3/qualityprofile/$id" \
  -H "X-Api-Key: $KEY" -H "Content-Type: application/json" \
  -d @profile.json

The Ultra-HD profile was left alone — the 4K library is supposed to allow Remux-2160p. With upgradeAllowed=false on the 1080p profile, Radarr won't auto-replace existing REMUX MKVs already on disk, only block new ones.

Then I deleted the 42 GB Blu-ray 3D ISO via DELETE /api/v3/moviefile/{id} and let Radarr re-search. A Bluray-1080p x264 replacement landed within minutes, about an eighth the size, and Emby direct-played it.

A few days later I followed up by purging the rest of the REMUX/BR-DISK files that were no longer profile-allowed — 521 movie files, about 13.4 TB. Chunked the re-searches into batches of 100 against MoviesSearch so I didn't blow up the queue, and the library settled at the new cap.

What I'd do differently

I'd set the quality profile to the transcode reality from day one. The instinct to grab the biggest, "best" copy is wrong for a server with no GPU passthrough and a residential WAN. The right ceiling is whatever your weakest playback path can handle without ffmpeg getting involved.