Start with the exact error message. Note whether the failure happens while opening the source, encoding, writing the output, optimizing or adding it to the TV app. Keep the original and avoid automatically retrying an entire batch.
Check the basics
- Confirm the source still exists and can be read in Finder.
- Try playing it. Check several positions; a file that opens can still contain damaged sections.
- Confirm the destination is available and writable.
- Check free space on the destination and the Mac's startup volume, which may be used for temporary work.
- Process the file by itself and record the preset and active rules.
Narrow down the cause
If using a NAS or external drive, compare a local source copy and local destination. Then try a different known-good file with the same preset. If only one file fails, keep its track information and error details. If many files fail at the same stage, focus on the shared settings, permissions or storage.
If output creation succeeded but TV-app import failed, check Automation permission and try importing the finished file manually. That separates a library-control issue from a conversion issue.
Report the result
Send the error, reproduction steps, app/macOS versions, preset and whether the local or known-good comparisons worked. If a partial output exists, describe it; its presence alone does not prove the job completed. Do not delete your only source as part of troubleshooting.