How to Merge MP4 Files with Different Frame Rates and Different Audio Sample Rates?

Question

I have four MP4 files that I wish to merge into one file. Let's call these four files the following: file_1, file_2, file_3, and file_4. I want to merge the files in the following order: file_1, file_2, file_3, and file_4.

file_2, file_3, and file_4 each have the following characteristics:

frame width = 640, frame height = 480, frame rate = 30 frames/second, audio sample rate = 48kHz

file_1 has the following characteristics:

frame width = 640, frame height = 480, frame rate = 29 frames/second, audio sample rate = 44kHz

Using the "append" feature in Avidemux 2.5.4, I merged file_2 and file_3 into file_2_3, with the audio and video remaining in sync in file_2_3. Then, once again using the "append" feature in Avidemux 2.5.4, I merged file_2_3 and file_4 into file_2_3_4, with the audio and video remaining in sync in file_2_3_4.

Then, I merged file_1 with file_2_3_4 into file_1_2_3_4. However, the audio and video in file_1_2_3_4 were not in sync. When file_1_2_3_4 is played, everything is OK during the file_1 portion. However, starting with the file_2 portion, the audio and video go out of sync.

Then, I tried to merge file_2_3_4 with file_1 into file_2_3_4_1. When file_2_3_4_1 is played, the file_2_3_4 portion is OK. However, the audio and video go out of sync in the file_1 portion.

So, I used Avidemux 2.5.4 to change the frame rate on file_1 to 30 frames/second. The frame width, frame height, and audio sample rate remained the same. Once again, I used Avidemux to merge file_1 with file_2_3_4 into file_1_2_3_4. Once again, starting with the file_2 portion, the audio and video go out of sync.

So, what do I have to do to make sure that audio and video are in sync throughout file_1_2_3_4? Should I convert the audio sample rate of file_1 to 48 kHz? What software do I use to do this? I heard of a software tool called MP4 Joiner (http://www.dvd-tool.com/mp4-joiner.html) Will this help?

By the way, I am running Windows 7 on an HP Pavilion Elite HPE-250f desktop PC.

Thank you very much for any information and help.

Answer 1

You're going to need to re-encode file_1 as 30 frames/second. You can do this with x264 or mencoder or one of a very large number of freeware encoding utilities. You can't just join the files together if they don't have the same framerate. You will also need to reencode the audio to be the same sample rate. I suggest using sox to modify the wave form and then recompress with whichever codec you're already using.