Protect the recording you have
Make a separate copy before trying to repair the file. Leave the original name and contents intact, and choose a new output name for every attempt. A damaged recording is not something to repeatedly overwrite while experimenting.
If the file is still on the recording device, check whether the app or device has its own completion or recovery option. Also check whether you have a second copy that was saved before the interruption. A complete copy is more useful than a repair of an incomplete one.
Renaming .mov to .mp4 changes the filename, not the container information inside it. A different player may be worth trying on a copy, but a player cannot make missing source data appear.
What the error does—and doesn’t—mean
In a regular MP4 or MOV, the movie index describes how recorded media should be read, including its tracks and timing. A recording that stops before finalization may leave media data without the information needed to use it. The message can also appear when that information is damaged or unreadable.
The important question is whether the media data you need is still present. Rebuilding an index can help make existing data readable. It cannot restore frames or audio that were never written, were overwritten or are no longer in the file.
If the file is still readable
If you already use FFmpeg, inspect a copy before trying a remux. This example reads container information and does not write to the recording:
ffprobe -v error -show_format -show_streams "recording-copy.mp4"When streams can be read, a new container may be enough to make an otherwise readable file work in another application. A basic remux copies encoded streams into a new output:
ffmpeg -i "recording-copy.mp4" -c copy "remuxed-copy.mp4"If the input cannot be opened because its movie index is missing, that command may stop at the same error. Repeating it with a different output name is not a recovery method.
FFmpeg’s +faststart option relocates an existing movie index to the beginning for playback. It is not a general way to reconstruct an absent index. See the FFmpeg MOV/MP4 format documentation.
When a healthy reference matters
A recovery path may need recording parameters that the damaged file no longer provides. A healthy reference from the same camera, phone or app can help, but “another MP4” is not a meaningful match.
Use a healthy clip made with the same recording setup where possible: codec, resolution, frame rate, audio codec, sample rate, channel layout and number of audio tracks. If settings changed between recordings, say so rather than assuming the new clip matches.
A short recording made now may be useful if you can reproduce the original settings. Do not damage that clip on purpose. Do not borrow an unrelated file as a template. A readable reference can still be a poor match; a reference that cannot itself be read needs to be replaced.
What a MendVid attempt would involve
The intended flow begins with file selection and clear payment terms. The repair-attempt fee is paid before repair runs or any result is shown. The repair-attempt fee is US$9.99 per video. Applicable tax is shown at checkout.
The documented local repair workflow tries applicable methods and checks candidate outputs, including video decoding, audio tracks and timing. Its results distinguish recovered, partial, reference-required and failed states. A candidate that merely exists on disk is not enough to call a repair successful.
If a reference is requested, it belongs to the same paid job. You should not have to pay again to provide it. A recovered or partial result can then be reviewed through a watermarked sample. The sample is generated from the recovered result and contains a prominent burned-in watermark.
Check more than “it plays”
For a real output, compare what you can against the recording you expected. Look at the opening, important middle sections and ending. Listen to each expected audio track. Check whether the duration makes sense and whether sound still matches the picture.
Clean decoding is useful evidence of readability. It is not proof that every original frame survived, that every sound is present or that precise synchronization has been preserved. A shortened video or a missing audio track should be reported as partial recovery.
Some repair paths may rebuild the video clock by re-encoding video while copying audio. That should be disclosed. It is not a lossless video remux, and it is not a blurry-to-sharp quality enhancement.
Capability basis: the approved MendVid brief and the two supplied local repair/router-validation documents, reviewed 31 October 2026. The current evidence describes a local CLI, not an operating public upload service. See also the guide to interrupted OBS recordings for ordinary and Hybrid formats.