How to Convert Underwater Diving Videos to MP4 on Your Phone
Once you start shooting underwater video on an action camera like the Insta360 Ace2 Pro, the next problem you run into is "the file's too heavy to share." Even beautiful footage of the seas in Kerama or Shakotan can get rejected with "file too large" when you try to send it over LINE. This article, written by a diver, covers how to convert and compress underwater video to MP4 entirely on your phone, for sharing.
In short, converting and compressing your underwater video's resolution to MP4 with the free app MediaToolbox shrinks it to a size you can share directly on LINE or social media, no computer required.
Why Is Underwater Video Hard to Share?
An action camera like the Insta360 Ace2 Pro shoots underwater with strong stabilization and beautiful color, but shooting at a high-quality setting like 4K/60fps can easily produce a file hundreds of MB to several GB even for just a few minutes of footage. As covered in How to Take Underwater Photos, getting a beautiful shot is genuinely appealing, but it also means a heavier file, and trying to send it directly over LINE or email often runs into a size-limit error.
How Do I Convert and Compress Underwater Video to MP4?
You could transfer it to a computer and re-export with editing software, but you often won't be carrying a computer around while traveling or near a dive shop. Converting to MP4 by specifying a resolution with a phone app lets you finish the whole process on the spot, ready to share in just a few taps.
How Do I Convert Underwater Video to MP4 in MediaToolbox?
- Open MediaToolbox and select "Resize Video"
- Choose the underwater video imported from your action camera
- Select an output resolution from 1080p, 720p, or 360p, matching where you'll share it
- Tap "Convert & Save" and it's converted and compressed to MP4, saved to your device
The lower the resolution, the smaller the file size, so choosing based on where you're sharing it is the key.
What Resolution Should I Use for Each Destination?
| Destination | Recommended resolution | Notes |
|---|---|---|
| Sending to diving buddies on LINE | 360p–720p | Prioritize file size — plenty to convey the underwater atmosphere |
| Posting on social media | 720p | Sufficient quality for viewing on a phone screen |
| Keeping for editing / archiving | 1080p | Prioritizes quality while still being lighter than the original 4K |
Are There Other Ways to Keep a Record Besides Video?
If you have video where you narrated something you noticed underwater, MediaToolbox's "Extract Audio" feature can pull just the audio out as an M4A file. It's also handy for listening back to as a memo after diving. Alongside your video records, keeping data like depth, water temperature, and visibility in a logbook makes the memory come back much more vividly when you look back later.
Summary
Underwater video shot on an action camera tends to have a heavy file size precisely because it looks so good, but adjusting the resolution with MediaToolbox and converting to MP4 shrinks it to a size you can share on LINE or social media, entirely on your phone, no computer required. Give it a try and share your ocean footage from Kerama or Shakotan with your friends.
MediaToolbox
A simple multimedia conversion tool for video, images, audio, and PDF — all in one. Free.
📲 Download for freeFrequently Asked Questions
Q. Why does underwater video from an action camera end up so large?
A. Because it can shoot at high resolution and frame rate, a setting like 4K/60fps can easily produce a file hundreds of MB to several GB even for just a few minutes of footage.
Q. Can MediaToolbox also correct underwater video's color?
A. MediaToolbox is centered on resolution conversion, compression, and format conversion. For underwater-specific color correction, using your camera's own shooting mode or a separate editing app is recommended.
Q. What resolution should I use for a converted video I'm posting on social media?
A. Around 720p is usually plenty of quality for social media. For saving or watching back later, 1080p is recommended.
Q. Can I pull just the audio out of an underwater video?
A. Yes. MediaToolbox's "Extract Audio" feature can pull just the audio out of a video as an M4A file.
Q. Does the conversion happen entirely on-device?
A. Yes. Conversion in MediaToolbox is processed entirely on-device, so there's no need to upload your underwater video to an external server.