Chromecast 4K fails with transcoding disabled (should be supported)

[mahi]

I only have a Raspberry Pi so I can't do transcoding (for now), and thus I've disabled it for all users completely.

When playing through the Jellyfin mobile app or directly through my Samsung S90C, the video works fine.

But when casting from Jellyfin mobile to Chromecast, I get the "this client isn't compatible with the media and the server isn't sending a compatible media format" error.

Using HandBrake I can see the video and audio codecs, on summary tab:

H.264 (x264), 30 FPS PFR
AAC (avcodec), Stereo
Foreign Audio Scan, Burned
Chapter Markers

And on audio tab:

E-AC3, 5.1 ch, 384 kbps, AAC, 160 bitrate

This should all be supported by the Chromecast 4K (with Google TV), but when I try to play it fails. This has repeated itself on multiple different medias that should work fine according to Google's Chromecast specs.

Two questions:
1. What's wrong here, why isn't it working? How can I debug this?
2. Can I do transcoding on my mobile or my TV? Both should be fast enough, but if I enable transcoding then it's done on the Raspberry Pi server only.

[TheDreadPirate]

In the jellyfin log there is a field called "TranscodeReason". What does it say? Also, in your CCwGTV, are you telling the client to downmix 5.1 to stereo? That would trigger an audio transcode. In the Android TV client, click on the gear in the top right, Playback, and about halfway down are various audio settings. Fiddle around with those.

Can you share your logs with us via https://sourceb.in/ ?