I want to merge an audio file (.wav or .au format) with a video file (.mp4 format).

Please suggest me how to achieve this. I want to merge these file to new .mp4 video file. An ffmpeg command would be very welcome.


8 Answers 8


Merging video and audio, with audio re-encoding

See this example, taken from this blog entry but updated for newer syntax. It should be something to the effect of:

ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac output.mp4

Here, we assume that the video file does not contain any audio stream yet, and that you want to have the same output format (here, MP4) as the input format.

The above command transcodes the audio, since MP4s cannot carry PCM audio streams. You can use any other desired audio codec if you want. See the FFmpeg Wiki: AAC Encoding Guide for more info.

If your audio or video stream is longer, you can add the -shortest option so that ffmpeg will stop encoding once one file ends.

Copying the audio without re-encoding

If your output container can handle (almost) any codec – like MKV – then you can simply copy both audio and video streams:

ffmpeg -i video.mp4 -i audio.wav -c copy output.mkv

Replacing audio stream

If your input video already contains audio, and you want to replace it, you need to tell ffmpeg which audio stream to take:

ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 output.mp4

The -map option makes ffmpeg only use the first video stream from the first input and the first audio stream from the second input for the output file.

  • I tried it but ffmpeg is freezing while merging
    – Sandy
    Commented May 1, 2011 at 11:41
  • 8
    i don't think mp4 containers can have wav audio streams. Try ffmpeg -i audio.wav -i video.mp4 -acodec copy -vcodec copy -f mkv output.mkv
    – Luke
    Commented Mar 12, 2013 at 23:29
  • 1
    I am using this and it is replacing the origional audio from the input audio. What if I want to merge input audio with the audio of input video? Commented Jan 31, 2014 at 7:00
  • Great, I used ffmpeg -i video.mp4 -i audio.wav \ -c:v copy -c:a aac -strict experimental output.mp4 to merge MP3 with Wav file...=> mp4 5 minutes, rendered 30 seconds..Thanks
    – sonida
    Commented May 24, 2015 at 18:55
  • About the "Replacing audio stream", will it work even if there is no audio in the video file? And how can I make the audio loop in case it's too short compared to the input video? I've also noticed that if the audio is longer than the video, the output video will be as long as the audio file. Is there a way to overcome it? Commented Feb 24, 2019 at 12:35

Since I am not allowed to write comments to the first answer with my reputation, an addendum here, because I had this problem when encoding webms.
If your audio stream is for example longer than the video stream, you have to cut it or otherwise you will have the last video frame as a still image and audio running.

To cut either stream, you can use -ss [hh:mm:ss] -t [ss] before each of the -i "file.ext".
-ss [...] will define the starting point to cut
-t [...] will define the length of the segment in seconds


ffmpeg.exe -ss 00:00:10  -t 5 -i "video.mp4" -ss 0:00:01 -t 5 -i "music.m4a" -map 0:v:0 -map 1:a:0 -y "out.mp4"

Example with shortest:

ffmpeg -i "video.mp4" -i "music.m4a" -c:v copy -map 0:v:0 -map 1:a:0 -shortest "out.mp4"
  • 27
    You can also just use -shortest to cut the end.
    – user55479
    Commented Mar 25, 2016 at 15:22

Open command promt (windows+R -> Cmd+Enter). Then go to inside the folder where you have audio and video file. Apply this command:

ffmpeg -i "videoFile.mp4" -i "audioFile.mp3" -shortest outPutFile.mp4

You will get a new file named outPutFile.mp4 (a merged file of audio and video)

  • 3
    It's really not necessary to describe how to use the command line here. It's pretty much implied that users will be able to figure that out. Especially since the asker specified FFmpeg. All the same, the -shortest tag is very nifty. Much simpler than in @user136036's answer.
    – Kat
    Commented May 14, 2015 at 17:08
  • 6
    This will re-encode everything, which is probably not what is wanted.
    – mivk
    Commented Nov 2, 2015 at 22:00
  • 'ffmpeg' is not recognized as an internal or external command,
    – UniCoder
    Commented Dec 8, 2016 at 12:24
  • You have to add ffmpeg to PATH wikihow.com/Install-FFmpeg-on-Windows
    – Arete
    Commented Mar 27, 2017 at 16:14

This worked for me:

ffmpeg.exe -i AudioT.m4a -i VideoT.mp4 -acodec copy -vcodec copy muxed.mp4

Try using mencoder (Yes it is ffmpeg based, but you never know). I use the -audiofile argument. I generally use ffmpeg, though, so take this advice with a pinch of salt.

And, if you use Windows, Mediacoder (not open source anymore sadly) works... its basically a frontend for a lot of gnu encoders and a few non-free ones.


In case one would like to merge audio and video with different length and also to apply Fade In and Fade Out the following worked for me:

ffmpeg -i Video001.mp4 -i Audio001.mp3 -af afade=t=in:st=0:d=3,afade=t=out:st=47:d=4 -c:v copy -c:a aac -shortest Output.mp4

In my case above the video was of length 51 so I chose Fade In of length 3 [Sec] and Fade Out* of ~4 [Sec]. Since fading is applied by a filter it required transcoding of the audio. In the case above I chose aac encoding.

The answer is heavily based on the answer of @PatrickGeorgi.


I've made a Python script to do this, you can try it if you want. Get it on github: https://github.com/mmakarov/replicator

Or look at video here: https://www.youtube.com/watch?v=4Uu1hS3-eQM

Replicator is a Python script to merge a few video files, transparent overlay, text areas with mp3 audio track. Final video will be exact same length as your audio track. Lenght of your video will be calculated automatically.

I've make this script in a try to merge any video sequence files with PNG transparent overlay, adding text areas on video, with mp3 audio track. Resulting video file are ready to upload on Youtube or any other video hosting services.

You can change it on your taste.

How to use it: 0. Open terminal and enter: git clone https://github.com/mmakarov/replicato...

  1. Put your video files to project directory as 'source1.mp4', 'source2.mp4', etc
  2. Put your PNG transparent image to project directory as 'overlay.png'
  3. Put your MP3 file to project directory as 'voice.mp3'
  4. in terminal run: python3 source-to-medium.py (here will be created 'medium.mp4')
  5. enter your text areas contents if needed ...it takes some time to convert source*.mp4 files to one medium.mp4
  6. in terminal run: python3 medium-to-fin.py ...it will caltulate final video length dividing voice.mp3.length() / medium.mp4.length() = silent_fin.mp4.length() ...also it will add voice.mp3 to silent_fin.mp4 as audio track
  7. Finally you've got youtube_ready.mp4 files

Warning: russian comments in sources!


-map can be used to produce an English mashup from two mp4 video sources with varying English and foreign language properties:

  • video-sub.mp4 - a foreign video containing English subtitles, but with a foreign audio track
  • video-dub.mp4 - a foreign video containing foreign text, but has an English dub audio track

To an English mashup that has English subtitles and an English dub audio track:

ffmpeg -y \
       -i video-sub.mp4 \
       -i video-dub.mp4 \
       -vcodec copy \
       -acodec copy \
       -map 0:v:0 \
       -map 1:a:0 \

You'll see that -vcodec copy and -acodec copy are used so no decompression and recompression will occur. This requires that the source videos, idealistically, are the same format resolution and the same duration.

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