I have two MP4 files that I generated with Camtasia Studio. I need to join them together post rendering with Camtasia (it can't be done during the Camtasia rendering process). Looking for a utility or technique that will work to join these, preferably that doesn't require re-rendering all the video again.

Update: Either Windows (preferred) or Mac. Doesn't need a GUI if it is a good command-line app.


5 Answers 5


I think the simplest way to this is to use MP4Box.

./MP4Box -add file1.mp4 -cat file2.mp4 -cat file3.mp4 output.mp4

I was encountering audio sync issues when trying to do this with Avidemux, but I came upon a two-step process that keeps the audio in sync:

  1. Concatenate files using MKVToolNix (I used version 7.4.0 for Mac). This results in a Matroska video (.mkv) file.
  2. Remux the .mkv file to MP4 format using Avidemux (I used verison 2.6 for Mac). I chose the MP4v2muxer option in the Output Format section. This results in an MP4 file with audio and video in sync.

Avidemux should do the work.

  1. Load File
  2. Go to File -> Append and select File
  3. To the left of the video window,
    • set video mode to Copy;
    • same for audio mode;
    • set format to MP4.
  4. Go to File -> Save -> Video.
  • This does what I am looking for, but it is causing the audio to go out of sync at the join point. I am going to try and join and mix the audio from a separate channel. Commented Apr 3, 2012 at 17:43

I would suggest using ffmpeg, and the -vcopy switch. Usually this will work, but it depends on codec support.

Various builds of it have various codecs. If one version of it doesn't work, try downloading a copy from a different site.


i think MPEG Streamclip can do this. It's free on mac and pc.

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