A7S III RSV file: recovering an interrupted recording

Updated 3 November 2026

If your A7S III stopped mid-take because the battery ran out, the card was pulled or the camera was switched off, the card now holds a .RSV file where the .MP4 should be. This is the camera we have tested most, so this guide can be more precise than the others: what is inside the file, which modes we have rebuilt, and what to expect when you open the result in your editor.

What is inside an A7S III .RSV file

The A7S III writes each recording as it goes: video frames, sound and a stream of Sony metadata, repeated in small groups. The index that ties them together (where each frame is, how long it lasts, which frames are key frames) is written only when you press stop. That is the part an interrupted .RSV is missing. More on that in What is an RSV file?

What makes the A7S III easy to work with: the first block of metadata in the recording also carries the codec settings the video needs to be decoded (in technical terms, the H.264 SPS/PPS or the H.265 VPS/SPS/PPS). That means the file can be rebuilt from itself. You don't need a "reference" clip recorded in the same mode, which many repair methods ask for.

Protect the card first

1. Stop using the card. Don't format it, don't record on it and don't delete anything, including the .RSV. Put a different card in if you have to keep shooting.
2. Copy everything. With a card reader (CFexpress Type A cards need a reader that supports them), copy the entire PRIVATE folder to your PC. Your clips are in PRIVATE/M4ROOT/CLIP.
3. Check the second slot. If the camera was recording to both cards at once and only one was removed, the other one may hold the finished .MP4. After a dead battery, both cards will usually hold an .RSV.

Free first try: put the card back in the camera

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 is worth trying on the A7S III once you have a copy: insert the card in the same slot, switch on with a charged battery and wait. If a recovery message appears, let it complete. Then look in PRIVATE/M4ROOT/CLIP for a new .MP4 with the same number. If the .RSV is still there and no .MP4 appeared, move on to the repair.

Rebuilding the MP4 with Lazaclip

Lazaclip is our Windows 10/11 program (we make it, so we are not neutral). On an A7S III file it reads the codec settings from the recording itself, rebuilds the index and saves a normal .MP4. Steps:

1. Open the card in the reader, the folder you copied, or the single .RSV file.
2. Click Preview 10 s to see the start of the take with a trial watermark. Scanning and the preview are free.
3. With a license, save the full video to your PC, or repair every .RSV on the card with Repair all.

The video and audio data are copied as they are, not re-encoded. The .RSV is opened read-only and the program won't write results back onto the card.

Modes we tested on the A7S III

We tested on original A7S III recordings (firmware from 2020) cut off at several points to imitate a power cut. In each case the rebuilt file had video frames and audio identical to the original recording, up to the last unfinished group of frames before the cut. Modes we haven't tried, such as slow and quick motion or 4-channel audio, may behave differently; the free preview shows whether the program can read your file before you pay.

Opening the repaired file in your editor

• XAVC HS (H.265): some players and editors need HEVC support to play it. In Windows' own apps that may mean installing Microsoft's HEVC video extension. That is about your PC, not the repair.
• XAVC S 10-bit 4:2:2: many graphics cards can't decode this format in hardware, so playback can stutter in some editors. The camera's own healthy clips in that mode will behave the same way.
• S-Log3 and HLG look flat or pale in the watermarked preview, which is converted for quick viewing. The saved .MP4 is your original data, ready for grading.
• XAVC S-I files are large; make sure the drive you save to has space for a copy of the whole .RSV.
• The camera's sidecar .XML file for the interrupted take may be missing. If your editor uses it, check that clip after import.

Preventing the next one

• Long 4K takes use a lot of battery. Change batteries between takes, not during one.
• For long takes, consider external power; check the A7S III manual for the supported power options while recording.
• Recording to both slots at once gives you a second copy of every take.
• Wait for the camera to finish writing before you open the card door or switch it off.

Shooting on an FX3 as well? See the FX3 guide. For an FX30 as a second camera, see the FX30 guide.