Why repair tools ask for a reference video
An MP4 or MOV recording keeps two things in its index, the moov atom: where every frame sits, and the settings a decoder must read before it can draw the first picture. For H.264 those settings are the SPS and PPS; for H.265 (HEVC) there is a VPS as well; for AAC sound there is a short audio configuration. When a recording stops before the index is written, the frames survive and the settings go with the index.
A healthy video from the same camera, recorded at the same resolution and frame rate, carries the same settings. That is all a reference file is for: a tool copies its settings and reads the broken footage with them. No picture or sound is taken from it.
How this tool gets by without one
It tries three things before it asks you for anything:
- Settings inside the footage. Some cameras repeat their settings in front of every key frame. Those files never needed a reference; the tool reads the settings where they are.
- Settings worked out from the footage. When the settings exist only in the lost index, the tool reads the first frames under candidate settings, drawn from its library of real phone and camera recordings, and keeps the one the frames read cleanly under. The free preview shows you the result before you pay.
- Sound from its own frames. The AAC sound's configuration is worked out from the audio frames themselves when enough of them prove it.
Only when none of that can be proven does it ask for a clip from the same camera. It tells you before you pay anything.
What we tested
We took real recordings, removed the index from each, repaired them, and compared every picture and every sound frame with the original using ffmpeg's per-frame checksums.
| Recording | Video | Reference needed? | Result |
|---|---|---|---|
| Samsung Galaxy A56, 1080p | H.264 + AAC | No | 352 of 352 pictures and 277 of 277 sound frames identical |
| DJI camera, 4K | H.265 | No (settings inside the footage) | 212 of 212 pictures identical |
| Our own 1080p test recording | H.264 + AAC | No | 450 of 450 pictures and 705 of 705 sound frames identical |
| GoPro HERO6 | H.264 + AAC | Yes | With a clip: 707 of 707 pictures and 1,106 of 1,106 sound frames identical |
| GoPro HERO10 | H.265 + AAC | Yes | With a clip: 1,384 of 1,384 pictures identical |
| 70mai dash cam, front, 4K | H.265 | Yes | With a clip: 35 of 35 pictures identical |
| iPhone, 1080p | H.264 + AAC | Yes | With a clip: 122 of 122 pictures identical |
So the honest answer is: often, not always. Phones whose footage proves its settings come back alone; GoPro, the DJI Avata and the iPhone files we tested still need a clip.
Try it without a reference first
- Copy the broken file to your computer and open it in the checker on this page. Your browser reads it from your disk; nothing is uploaded.
- The free check reads the footage and tells you whether it can rebuild the file on its own.
- Press Repair and watch the free 5-second preview.
- If the checker asks for a clip, add any video that plays from the same camera, recorded at the same resolution, frame rate and video format. A clip from the same day is the safest choice. If you have none, record ten seconds with the same settings.
On Android, the Video Repair app does the same on the phone, and looks for that clip among your videos by itself when one is needed.
When you still need a reference
- Cameras that write their own layout. GoPro and DJI drones store data between the frames; the tool reads it from a healthy clip of the same camera.
- Settings the frames can't prove. A recording with very few frames, or one whose first key frame was damaged, leaves too little to check a guess against.
- A different camera mode. A clip recorded at another resolution, frame rate or HDR setting carries other settings; the checker says so instead of producing a picture that doesn't decode.