Hi,

It is quite surprising and unpleasant when CapCut doesn't behave as expected, especially when it cuts your video short in CapCut.

Since this only happens with some MP4 files and not others, it suggests the issue might be with the specific characteristics of those particular files, or how CapCut interprets them, rather than a universal CapCut bug affecting all MP4s.

Here are some common causes and troubleshooting steps you can try:

1. Corrupted Video File:

   • Problem: The MP4 file itself might be corrupted or incomplete, even if it plays mostly fine in a standard player. The metadata might indicate a 20-minute length, but the actual video data stream could be damaged or end prematurely.
   • Test: Try playing the original problematic 20-minute MP4 file in a different media player (like VLC Media Player, Windows Media Player, or QuickTime). Does it play fully to the end without issues? If it also stops early or glitches in other players, the file itself is likely the problem.
   • Solution: Try re-downloading, re-copying, or re-exporting the source video file.

2. Variable Frame Rate (VFR):

   • Problem: Many video editing programs, including CapCut, can struggle with videos recorded with a Variable Frame Rate (VFR). This is common in screen recordings or footage from smartphones. The fluctuating frame rate can confuse the editor about the video's true length or cause sync issues.
   • Test: You can often check if a video is VFR using tools like MediaInfo (a free utility).
   • Solution: Convert the video to a Constant Frame Rate (CFR) before importing it into CapCut. Tools like Handbrake (free, open-source) or Shutter Encoder (free) are excellent for this.
     • In Handbrake: Load the video, go to the 'Video' tab, and select 'Constant Framerate'. Choose a standard frame rate (like 24, 25, 30, or 60 fps). Also, ensure a standard codec like H.264 (x264) is selected. Then, re-encode the video.

3. Incompatible Codec or Encoding Settings:

   • Problem: While the container is MP4, the specific video or audio codec used inside might be unusual or have settings that CapCut doesn't fully support, leading to import errors.
   • Solution: Similar to the VFR solution, transcode the video using Handbrake or Shutter Encoder to a very standard format: MP4 container, H.264 video codec, AAC audio codec, Constant Frame Rate. This often resolves compatibility issues.

4. CapCut Cache Issues:

   • Problem: Sometimes, CapCut's temporary cache files can become corrupted, leading to unexpected behavior during import or editing.
   • Solution: Clear CapCut's cache.
     • Mobile: Go into CapCut's settings within the app. Look for an option like "Clear Cache". The exact location might vary slightly between iOS and Android versions.
     • Desktop: In CapCut Desktop, go to Settings > System (or similar) and find the "Clear Cache" option. You might need to close and reopen CapCut afterwards.

5. Insufficient Device Resources:

   • Problem: Particularly on mobile devices, importing or processing very long or high-resolution videos can strain the device's RAM and storage. This could potentially lead to incomplete imports if resources run out. Check if your device has sufficient free storage space.
   • Solution: Ensure you have plenty of free storage space on your device. Close other background apps before importing into CapCut. If possible, try importing on a more powerful device (like a desktop computer if you were using mobile).

6. CapCut Version Bug:

   • Problem: It's possible a specific version of CapCut has a bug related to importing certain types of MP4 files.
   • Solution: Ensure CapCut is updated to the latest version available from your app store (mobile) or the official website (desktop).

Troubleshooting Steps Summary:

1. Verify the Original File: Play the full video in another player (like VLC).
2. Convert to CFR: Use Handbrake/Shutter Encoder to convert the video to Constant Frame Rate (H.264/AAC is a safe bet). Try importing this new version.
3. Clear CapCut Cache: Clear the cache within the CapCut app settings.
4. Update CapCut: Make sure you're using the latest version.
5. Check Device Storage: Ensure you have enough free space.
6. Restart: Restart both CapCut and your device.

Start with step 1 and 2, as file corruption or VFR are very common culprits for this type of issue. Good luck, and we hope one of these steps resolves the problem.

Or if you can send the MediaInfo of the video, we can take a look at the file structure for you.