I'm on MacOSX Lion and would like a method for converting webm to mp4 (or another iTunes compatible format). ffmpeg seems like a possibility but the documentation is a bit obtuse for me; step-by-step directions would be appreciated.

  • 1
    You can also use Handbrake if that's already installed. It's a beautiful, open source GUI around ffmpeg and does the trick very nicely and easily. handbrake.fr – Joshua Pinter Apr 25 '20 at 16:32

Get FFmpeg

If you want to use ffmpeg, go and either

If you downloaded it manually (not with Homebrew), I would suggest copying the ffmpeg executable file to your PATH, so that you can use it from the Terminal. Let's say you downloaded it to ~/Downloads/ffmpeg/ffmpeg, then do:

sudo mkdir -p /usr/local/bin
sudo cp ~/Downloads/ffmpeg/ffmpeg /usr/local/bin/
sudo chmod +x !$ /usr/local/bin/ffmpeg

Convert to MP4

Now, by "to MP4", I assume you mean to use H.264 and AAC as video and audio codecs, respectively. For that, the basic command would be:

ffmpeg -i input.webm -c:v libx264 -c:a aac -strict experimental -b:a 192k output.mp4

If you want to control the quality, have a look at the x264 encoding guide. It is set with the -crf option, where the default is 23, and lower means better quality (typical values are from 18 to 28). In the above example it uses the default quality of 23 for video, and 192 kBit/s constant bitrate for audio.

As for audio, the static builds do not support libfdk-aac, but if you have support for it, you should use that instead:

ffmpeg -i input.webm -c:v libx264 -c:a libfdk_aac output.mp4

FDK-AAC gives you better quality than the internal AAC encoder. For controlling audio quality, see the AAC encoding guide.

  • I successfully create MP4 files this way on FreeBSD (from MKV and WEBM), and can play them on FreeBSD with mplayer, but Apple refuses to open them... – Mikhail T. Feb 5 '17 at 8:30
  • Who is "Apple" in your case? QuickTime or Preview? Do you get any specific error message? What is the output of `ffmpeg -i <your-file>? – slhck Feb 6 '17 at 12:17
  • By "Apple" I meant their file-manager. It would not generate a preview-image from the file. Trying to play the video (by double-clicking) also resulted in an error message. Similarly, iMovie refused to open the file. – Mikhail T. Feb 6 '17 at 20:56
  • There may be something peculiar about your source that makes it fail. Like I said, the command you gave below creates a more or less "legacy" video with bad quality. Let me know what exactly fails and we'll figure it out. – slhck Feb 7 '17 at 8:06
  • Looks like the FDK-AAC param is now libfdk_aac (underscore instead of a dash). – twelve17 Mar 12 '17 at 8:36

This is, what I just used successfully on FreeBSD to create MP4-files, that MacOS would recognize as such:

ffmpeg -i input_filename -acodec aac -b:a 128k -vcodec mpeg4 -b:v 1200k -flags +aic+mv4 output_filename.mp4

I started with the command-line using this tutorial, but had change libfaac to aac because the latter was not found...

There must be some special kind of madness affecting programmers in the domain of multimedia codecs, that causes them to subtly change the command-line options from one release to another.

  • While this creates an MP4 container indeed, your command uses the (old) MPEG-4 Part II codec, which is different from the modern H.264 (see here), which means that your video quality will be lower for any given file size. I would recommend against using this codec. macOS should read H.264 video just fine. You could How to Ask a new question, including details on the video you created and your OS, then ping me and I'll have a look why it doesn't work. – slhck Feb 7 '17 at 8:00

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