Confirm which application reads the configuration
A configuration that works in the mpv executable is not automatically evidence that Celluloid has loaded that same file. Begin by identifying the actual player package and the configuration file you intend to use. Keep the existing configuration protected before editing it.
Choose one harmless observable option for the first test. Do not begin with a collection of display, decoder and network flags copied from several computers. A narrow comparison should make it possible to say whether the file was loaded without introducing a second playback fault.
Use the documented frontend activation step
Celluloid’s README says an mpv-syntax configuration file must be specified and enabled under MPV Configuration in Preferences. Inspect the actual selected path and enabled state. A file placed in a familiar directory alone is not the same observation as the frontend’s setting pointing to it.
Confirm the package can read the selected file through its supported access context. Keep the full path private if it contains personal directory names. If the file does not exist at the chosen location, resolve that input before changing the option syntax.
Keep extra options distinguishable
The project also documents an Extra MPV Options field. Inspect whether it contains an overlapping setting before assessing the file. Keep the current contents recorded and change only the option relevant to the comparison. Two places requesting different values can make a saved file appear ineffective.
Open the same known local sample and inspect the intended observable behavior. Record the configuration path, activation state and result. If the option is unsupported by the installed engine version, retain that exact message instead of treating every ignored effect as a path problem.
Expand only after a single option is proven
Once the small file has a clear effect, add further needed options one at a time. Keep a local record of which change affects which task. A configuration that loads is not a certificate that every advanced flag suits the current GPU, output driver or media source.
Retain a recovery route through the preferences and the original file. The expected outcome is an understood configuration input for the actual Celluloid package. It does not guarantee identical behavior in mpv, IINA or another frontend, and it does not establish that an imported configuration has been independently tested on your hardware.
Questions answered
Why is placing mpv.conf in a directory not sufficient evidence?
Celluloid documents selecting and enabling the file in its own preferences. Inspect that actual activation step.
What should be tested before importing many options?
Use one harmless observable option with a known local sample, then add only the changes needed for the actual task.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.