What is an RSV file?

Updated 3 November 2026

An RSV file (.RSV) is a video recording from a Sony camera that was never finished. You usually find one after the battery died, the card was pulled out or the camera was switched off while it was still recording. In the folder where your clips are, next to the normal C0041.MP4, C0043.MP4 and so on, there is a file such as C0042.RSV. It is often several gigabytes in size, yet nothing will open it.

The good news: in most cases the footage you recorded is still inside. What is missing is the part that lets a player find it.

Where .RSV files come from

Sony cameras that record XAVC S and XAVC HS video save it as an .MP4 file. While the recording is running, the camera writes the video and sound into a working file with the .RSV extension. When you press stop, it does two more things:

1. it writes the index of the recording: a table that says where every video frame and every block of sound sits in the file, how long each frame lasts and which frames are key frames;
2. it renames the file from .RSV to .MP4.

If the camera loses power, or the card disappears, before those two steps, you are left with the .RSV: all the recorded data, but no index. In the MP4 format, that index is the moov part of the file. Without it, a video player sees a large block of data and has no idea how to read it.

Why it won't open, and why renaming doesn't help

Video editors and players rely on the index to show the first frame, to seek and to keep picture and sound in sync. A file without one is rejected as damaged, or shows nothing at all.

Changing the extension from .RSV to .MP4 only changes the name. The index is still missing, so the result is the same. Re-encoding tools don't help either: they also need to read the file first.

To get a playable file you need to rebuild the index: go through the recorded data, find where each frame and each block of audio starts and ends, and write a new index for it. The video data itself doesn't need to be touched.

Is my footage really still in there?

Look at the file size. A clip that ran for a few minutes in 4K should be in the gigabytes. If the .RSV is about the size you would expect for the time you recorded, the data was written and can usually be rebuilt. If it is 0 KB or only a few kilobytes, the camera stopped before it wrote anything useful, and no tool can bring back what isn't there.

One part is always lost: the camera writes video in small groups of frames, and the group it was in the middle of when the power went is incomplete. In practice that means the last second or so before the cut.

What not to do

• Don't format the card, in the camera or on the computer, even if the camera suggests it.
• Don't keep recording on that card. Swap in another card and carry on with the shoot.
• Don't delete the .RSV file, even if it looks broken. It is the only copy of that take.
• Don't run "disk repair" or error-checking tools on the card before you have a copy.

The first steps, all free

1. Copy the whole folder to your computer. Put the card in a card reader and copy the entire PRIVATE folder (or at least PRIVATE/M4ROOT) to a drive with enough free space. Your recordings are in PRIVATE/M4ROOT/CLIP. Copy the healthy .MP4 files too: for some older cameras they help with the repair.
2. Try the camera itself. Some Sony cameras try to recover an interrupted clip on their own when you put the card back into the same camera with a charged battery. It doesn't happen with every model or every interruption, but it costs nothing, and because you already have a copy, you lose nothing by trying. If the camera shows a message about recovering or repairing data, let it finish without switching off.
3. Check the other card slot. If your camera has two slots and was set to record to both at once, and only one card was removed, the other card may hold a complete .MP4 of the same take.

How to recover an RSV file on Windows

If the camera didn't fix it, the file needs a new index. Lazaclip is our Windows 10/11 program that does exactly this (we make it, so take this section as coming from the seller). It works offline and never changes the original:

1. Open the card, the copied folder or a single .RSV file. The program lists every .RSV it finds and checks whether each one can be rebuilt.
2. Click Preview 10 s to watch the first ten seconds with a trial watermark. The scan and the preview are free.
3. With a license, save the full .MP4 to a folder on your PC, or repair every .RSV on the card in one go.

The video and audio are copied as recorded, without re-encoding; only the index is new. Newer cameras, such as the A7S III we tested, store the codec settings inside the recording, so nothing else is needed. Older cameras, such as the original a7S from 2014, don't store them; for those the program picks a healthy clip from the same card and the same recording mode as a reference, and checks it against the data before using it.

What can't be recovered this way

• Deleted files or a formatted card. If the .RSV is gone, you first need data recovery software to get the file back; rebuilding the index comes after that.
• MXF, X-OCN and XAVC (without the S) from Sony cinema cameras use other file formats.
• Recordings from other brands. Other cameras leave different kinds of broken files.
• Overwritten data. If you kept recording on the card after the interruption, part of the file may be gone for good.

How to avoid it next time

• Start long takes with a full battery and keep a charged spare at hand. Batteries drain much faster in the cold.
• For long events, consider external power, if your camera supports it (check its manual).
• Stop recording before you open the card door, and wait until the camera has finished writing before you take the card out or switch off.
• Replace a card that has given errors before, and format cards in the camera, not on the computer.

Guides for your camera

The steps are the same across Sony cameras, but the details differ. Pick yours: FX3, FX30, A7S III, A6700, ZV-E10 II and A7C II.