I want to join two mp4 files to create a single one. The video streams are encoded in h264 and the audio in aac. I can not re-encode the videos to another format due to computational reasons. Also, I cannot use any GUI programs, all processing must be performed with Linux command line utilities. FFmpeg cannot do this for mpeg4 files so instead I used MP4Box:

MP4Box -add video1.mp4 -cat video2.mp4 newvideo.mp4

Unfortunately the audio gets all mixed up. I thought that the problem was that the audio was in aac so I transcoded it in mp3 and used again MP4Box. In this case the audio is fine for the first half of newvideo.mp4 (corresponding to video1.mp4) but then their is no audio and I cannot navigate in the video also.

My next thought was that the audio and video streams had some small discrepancies in their lengths that I should fix. So for each input video I splitted the video and audio streams and then joined them with the -shortest option in FFmpeg.

Thus for the first video I ran:

 avconv -y -i video1.mp4 -c copy -map 0:0 videostream1.mp4
 avconv -y -i video1.mp4 -c copy -map 0:1 audiostream1.m4a
 avconv -y -i videostream1.mp4 -i audiostream1.m4a  -c copy -shortest  video1_aligned.mp4

Similarly for the second video and then used MP4Box as previously. Unfortunately this didn't work either. The only success I had was when I joined the video streams separately (i.e. videostream1.mp4 and videostream2.mp4) and the audio streams (i.e. audiostream1.m4a and audiostream2.m4a) and then joined the video and audio in a final file. However, the synchronization is lost for the second half of the video. Concretely, there is a 1 sec delay of audio and video. Any suggestions are really welcome.

  • "FFmpeg cannot do this for mpeg4 files so instead I used MP4Box" do you mean MP4 file ? do both the audio-video streams uses same encoding parameters (width,height, SPS,PPS, framerate, samplingrate, number of channels ?
    – rajneesh
    Dec 18, 2012 at 13:31
  • using ffprobe I see that the audio streams have identical attributes. The video streams have the same dimensions but different rates. For the 1st video Video: h264, 720x592, 277 kb/s, PAR 18944:12915 DAR 512:287, 24.97 fps, 45k tbr, 90k tbn, 90k tbc while for the second Video: h264, 720x592, 226 kb/s, PAR 481:330 DAR 39:22, 24.91 fps, 45k tbr, 90k tbn, 90k tbc . Do you believe that this is the source of my problems?
    – Jose Armando
    Dec 18, 2012 at 15:17
  • MP4 supports joining video/audio with different characteristics using different track for different video, but player are not that smart.
    – rajneesh
    Dec 18, 2012 at 16:13
  • try this stackoverflow.com/questions/5415006/…
    – daya
    Dec 18, 2012 at 16:37
  • Your question is already answered in ffmpeg FAQ: ffmpeg.org/faq.html#How-can-I-join-video-files_003f
    – Palec
    Dec 5, 2013 at 16:26

7 Answers 7


The best way to do this currently is with the concat demuxer. First, create a file called inputs.txt formatted like so:

file '/path/to/input1.mp4'
file '/path/to/input2.mp4'
file '/path/to/input3.mp4'

Then, simply run this ffmpeg command:

ffmpeg -f concat -i inputs.txt -c copy output.mp4

See also concatenation in ffmpeg FAQ.

I'm keeping the following here for the benefit of anyone using older versions of ffmpeg.

The latest versions of ffmpeg can do this: you'll have to remux the files into mpeg transport streams first (fairly processor-light, as it's only changing the container format):

ffmpeg -i input.mp4 -map 0 -c copy -f mpegts -bsf h264_mp4toannexb middle.ts

If that throws up an error [1] about h264, you may need to use:

ffmpeg -i input.mp4 -map 0 -c copy -f mpegts -bsf:v h264_mp4toannexb middle.ts

You'll have to do this separately with each input file. To concatenate the files together, use:

ffmpeg -i "concat:middle1.ts|middle2.ts|middle3.ts" -c copy output.mp4

If that throws up an error about aac, you may need to use

ffmpeg -i "concat:middle1.ts|middle2.ts|middle3.ts" -c copy -absf aac_adtstoasc output.mp4

If your system supports named pipes, you can do this without creating intermediate files.

mkfifo temp0 temp1

You'll have to do the following in three separate virtual terminals:

ffmpeg -i input0.mp4 -map 0 -c copy -f mpegts -bsf h264_mp4toannexb -y temp0
ffmpeg -i input1.mp4 -map 0 -c copy -f mpegts -bsf h264_mp4toannexb -y temp1
ffmpeg -f mpegts -i "concat:temp0|temp1" -c copy -absf aac_adtstoasc output.mp4

If output.mp4 already exists, the third ffmpeg will ask you whether you want to overwrite it, but it will do this after it has accessed the FIFOs, and this will make the first to ffmpegs close. So make sure that you choose an unused name for your output file.

This may not work if your input files are different - I believe that differences in bit rate are OK, but frame size, frame rate etc have to match up.

  • many thx mate, worked like a charm Dec 26, 2012 at 11:20
  • 2
    @DaveJarvis Not so; that's a message deliberately and maliciously spread by the libav team, who are a bunch of developers that split from the ffmpeg project to develop avconv (and changed the name because they couldn't secure the copyright on the ffmpeg name). See Who can tell me the difference and relation between ffmpeg, libav, and avconv? for a bit more information.
    – evilsoup
    Nov 16, 2013 at 14:29
  • 2
    *** THIS PROGRAM IS DEPRECATED *** This program is only provided for compatibility and will be removed in a future release. Please use avconv instead. is a message I see now on running ffmpeg
    – Lord Loh.
    Feb 1, 2014 at 22:11
  • @LordLoh. See the link in my previous comment.
    – evilsoup
    Feb 2, 2014 at 11:32
  • 1
    That answer does not answer - how to concatenate mp4 with avconv
    – Lord Loh.
    Feb 2, 2014 at 17:18

For mp4 the only working solution I found was with MP4Box from gpac package

for file in $(ls *.mp4|sort -n);do
    filesList="$filesList -cat $file"
MP4Box $filesList -new merged_files_$(date +%Y%m%d_%H%M%S).mp4

or command is

MP4Box -cat file1.mp4 -cat file2.mp4 -new mergedFile.mp4

with mencoder and avconv I could'nt make it work :-(

  • The command runs without apparent error (it just says creating track video+sound for file1.mp4 and then creating track sound for file2.mp4) .... and then I have no sound in the second part of the resulting video. mp4info says file1 has 1=video 2=audio, file2 has 1=audio, 2=video, maybe that's why... Apr 6, 2021 at 11:02

Here is a one-liner that makes it all that much easier. It does everything needed to be done in order to finally provide you with one resulting video file. Cheers!

find *.mp4 | sed 's:\ :\\\ :g'| sed 's/^/file /' > list.txt; ffmpeg -f concat -i list.txt -c copy output.mp4; rm list.txts
  • There is a typo at the end... This may work in the current directory. If you use find . -iname "*.mp4" | sort | sed 's:\ :\\\ :g'| sed 's/^/file /' > list.txt; ffmpeg -f concat -safe 0 -i list.txt -c copy output.mp4; rm list.txt you can get files in subdirectories ...
    – jaromrax
    Mar 11, 2021 at 14:58

Thanks for the script dvo. It was a great starting point for me. I had no problem with using named pipes so I adapted the script to use them instead. Plus I fixed it to work with filenames with spaces in them. Output to named pipes does not "go" until you begin reading from them, hence the need to background the initial remux tasks with an & before the final call to avconv. Plus, don't forget to use -c copy, or you end up re-encoding the whole lot.

for FILE in "$@"; do
   TAG=$(echo "$FILE" | sed -e s/[^A-Za-z0-9.]/_/g)
   mkfifo $TAG.mp4concatpipe
   avconv -loglevel "quiet" -i "$FILE"  -f mpegts -c copy -bsf h264_mp4toannexb -y $TAG.mp4concatpipe &

avconv -i concat:$IN -c copy out.mp4
rm *.mp4concatpipe
  • For some reason this is giving me an "concat:first.m4v.fifo|second.m4v.fifo: No such file or directory" error.. even with quotes (-i concat:"$IN" or -i "concat:$IN"). MP4Box suggested in the other answer below however works great!
    – vorburger
    Aug 9, 2014 at 13:16
  • Same error when I try it. I wonder if the ".fifo" on line 6 shouldn't be ".mp4concatpipe" instead? This fixes the error for me, but then I get another error. Codec 'aac' (86018) is not supported by the bitstream filter 'h264_mp4toannexb'. Supported codecs are: h264 (27) Apr 6, 2021 at 10:50

On a Mac (macOS 10.13 High Sierra) I used the following with success:

for f in *.m4a; do echo "file '$f'" >> mylist.txt; done

Reorder as above similarly if necessary (note that the ./ was removed - the path was causing ffmpeg to throw the unsafe file name error).

Then I had to remove the codec and bitrate specified for the default MacPorts ffmpeg to like it:

ffmpeg -f concat -i mylist.txt  output.m4a
  • Welcome to Super User!, Please read the question again carefully. Your answer does not answer the original question which was about linux. If you believe that it will work on linux please add that so future readers have a clear understanding, other than that again welcome to superuser and thankyou for your input. Please take a couple of minutes and read:- superuser.com/help .Answering: superuser.com/help/how-to-answer.
    – mic84
    Nov 14, 2017 at 2:50

Thanks evilsoup; here is a little script to automate the process, using the more recent avconv.
BTW, named pipes did not work for me (output to them got stuck).


    for FILE in $@; do
      avconv -i $FILE -map 0 -f mpegts -bsf h264_mp4toannexb -c:v copy -y $FILE.tmp

    avconv -i concat:"$IN" out.mp4

    for FILE in $@; do
      rm $FILE.tmp

Have enjoyed great success with

for f in ./*.m4a; do echo "file '$f'" >> mylist.txt; done

you may need to reorder mylist.txt slightly

ffmpeg -f concat -i mylist.txt -c:a libfdk_aac -b:a 128k output.m4a

ffmpeg version 2.2.3

  • I ran this without -c:a libfdk_aac and it worked. I tried installing a couple of packages for fdk aac on Ubuntu and it did not work. Feb 12, 2021 at 12:59

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