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How to Merge a Folder of MP4 Files with FFmpeg (Revisted)

06 July 2014 • by Bob • FFMPEG, Video Editing, Scripting, Batch Files

I ran into an interesting situation the other day: I had a bunch of H.264 MP4 files which I had created with Handbrake that I needed to combine, and I didn't want to use my normal video editor (Sony Vegas) to perform the merge. I'm a big fan of FFmpeg, so I figured that there was some way to automate the merge without having to use an editor.

I did some searching around the Internet, and I couldn't find anyone who was doing exactly what I was doing, so I wrote my own batch file that combines some tricks that I have used to automate FFmpeg in the past with some ideas that I found through some video hacking forums. Here is the resulting batch file, which will combine all of the MP4 files in a directory into a single MP4 file named "ffmpeg_merge.mp4", which can be renamed to something else:

@echo off

if exist ffmpeg_merge.mp4 del ffmpeg_merge.mp4
if exist ffmpeg_merge.tmp del ffmpeg_merge.tmp
if exist *.ts del *.ts

for /f "usebackq delims=|" %%a in (`dir /on /b *.mp4`) do (
    ffmpeg.exe -i "%%a" -c copy -bsf h264_mp4toannexb -f mpegts "%%a.ts"
)

for /f "usebackq delims=|" %%a in (`dir /b *.ts`) do (
    echo file %%a>>ffmpeg_merge.tmp
)

ffmpeg.exe -f concat -i ffmpeg_merge.tmp -c copy -bsf aac_adtstoasc ffmpeg_merge.mp4

if exist ffmpeg_merge.tmp del ffmpeg_merge.tmp
if exist *.ts del *.ts

The merging process in this batch file is performed in two steps:

• First, all of the individual MP4 files are remuxed into individual transport streams
• Second, all of the individual transport streams are remuxed into a merged MP4 file

Here are the URLs for the official documentation on each of the FFmpeg switches and parameters that I used:

• Switches:
  • -bsf (bitstream filter)
  • -c (codec)
  • -f (format)
  • -i (input)
• Parameters:
  • aac_adtstoasc
  • copy
  • concat
  • h264_mp4toannexb
  • mpegts

By the way, I realize that there may be better ways to do this with FFmpeg, so I am open to suggestions. ;-]