I have an action camera, and it cuts my videos at 30 min in order to make sure the videos aren't over 4 GB in size. So when I record a video (In this example, that is 1 hour, 13 min) its cut into 3 parts, so I want to re-join them. Here is the thing. With some videos it works, and with others it does not. No settings have been changed on the camera, I have done no clipping, or cutting, or anything. Just drag and drip file one. File --> Append file 2. File --> Append file 3. Change setting to MP4muxer (The original file is MP4) and click save (Leaving all settings to the default copy) It starts to do its job, then is erroring out. The file it saved is the exact same length as the first file in the series (30 min) but won't seem to go past that. Now here is the thing. Sometimes, with the exact same camera, on the exact same settings, it works just fine. What is going on? What information (And please, how do I obtain that information) do you need from me to help diagnose this issue?