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Media Processing Commands

Instead of accessing some privacy-questionable websites, free and open-source command-line tools are useful in working with media files, like images, audio and video.

Image processing​

The convert command that comes with ImageMagick is a powerful image processing tool that provides several useful functionalities.

convert input_image.jpg -resize 50% output_image.jpg
  • To convert a JPG image into PNG format:
convert input_image.jpg output_image.png

It's possible to convert pages of a PDF file into individual PNG images using convert as well, albeit it requires a slightly longer command. jdhao's article clearly explains how to achieve this.

Video and audio processing​

FFmpeg is a popular and versatile media processing tool that enables a wide range of features, from converting formats, trimming to speeding up and slowing down videos or audios, and many other functionalities.

ffmpeg -fflags +genpts -r 15 -i raw.h264 -i input.mp4 -map 0:v -c:v copy -map 1:a -af atempo=0.5 -movflags faststart output.mp4

Here, the value 15 supplied after the -r option means the frame rate is halved (30 / 2 = 15), whereas atempo=0.5 means the audio speed is halved.

  • To convert a FLAC file into MP3 format:
ffmpeg -i input.flac output.mp3
  • To trim a video with starting and ending timestamps given (with audio cut accordingly as well):
ffmpeg -i "video.mp4" -ss 1:00 -to 2:00 -c copy "cut.mp4"

The command above generates a copy of video.mp4, named cut.mp4, with only the portion from the 01:00 to 02:00 position.

vid_list.txt
file '/path/to/file1.wav'
file '/path/to/file2.wav'
file '/path/to/file3.wav'
ffmpeg -f concat -safe 0 -i vid_list.txt -c copy output.wav