ffmpeg convert mkv to mp3 code example

Example 1: converting mp3 with FFMPEG

ffmpeg -i input.mp3 output.ogg

Example 2: how to transcode a video in python using ffmpeg

ffmpeg -i input.mkv -c:a copy -s hd720 output.mkv
This modifies the video to 1280x720 in the output, but you can set the width and height manually if you want:

ffmpeg -i input.mkv -c:a copy -s 1280x720 output.mkv
This produces the exact same output as the earlier command. If you want to set custom sizes in FFmpeg, please remember that the width parameter (1280) comes before height (720).