Preparing video for Matlab analysis

Typical video files, such as MP4 files with H.264 compression, are usually small in size and with high visual quality. Such files are suitable for visual inspection but do not work well for video analysis. In most cases, computer vision software prefers to work with raw data or other compression formats.

The Musical Gestures Toolbox for Matlab works best with these file types:

  • Video: use MJPEG (Motion JPEG) as the compression format. This compresses each frame individually. Use .AVI as the container, since this is the one that works best on all platforms.
  • Audio: use uncompressed audio (16-bit PCM), saved as .WAV files (.AIFF usually also works fine). If you need to use compression, MP3 compression (MPEG-1, Layer 3) is still more versatile than AAC (used in .MP4 files). If you use a bitrate of 192 Kbs or higher, you should not get too many artefacts.

Many people ask me how to convert from typical MP4 files (with H.264 video compression and AAC audio compression). The easiest solution (I think) is to use FFMPEG, the versatile command-line utility. Here is a oneliner that will convert from an .MP4 file into a .AVI file with MJPEG and PCM audio:

FFmpeg -i input.mp4 -c:a pcm_s16le -c:v mjpeg -q:v 3 -huffman optimal output.avi

The resultant file should work well in Matlab and other video analysis tools. We have included this conversion by default in the new Musical Gestures Toolbox for Python. So there, you can directly load an MP4 file, which will be converted to an AVI file using a script similar to the one above.

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Alexander Refsum Jensenius is a music researcher and research musician living in Oslo, Norway.