FFMPEG
FFMPEG is a FOSS for encoding audio and video: https://www.ffmpeg.org/
Audio
Re-encode .mp3 audio file as .wav
ffmpeg -i someaudiofile.mp3 someaudiofile.wav
Video
Re-encode to .mp4
ffmpeg -i input.MP4 output.mp4
Rotate video
Rotate 90 clockwise:
ffmpeg -i in.mov -vf "transpose=1" out.mov
For the transpose parameter you can pass:
0 = 90° counterclockwise and vertical flip (default)
1 = 90° clockwise
2 = 90° counterclockwise
3 = 90° clockwise and vertical flip
Use -vf "transpose=2,transpose=2"
for 180 degrees.
src: https://stackoverflow.com/a/9570992
Gif
Convert video to gif
Scale down 1080p video into 1/4: ffmpeg -i "input-video.mkv" -s 960x540 output.gif