Youtube:
youtube-dl -F [link]
>this should give you the list of available video and audio formats
>and then you do
youtube-dl -f [number]+[number] [link]
>first number has to be video, tho
>second number is optional if the first one doesn't say video only

Trim stuff:
>either
ffmpeg -ss 00:01:00.5 -i input.mp4 -to 00:02:01.1 -c copy output.mp4
>or, if you want to specify the duration in seconds
ffmpeg -ss 00:01:00.5 -t 60.6 -i input.mp4 -async 1 output.mp4
>the last one depends on fps
>say, you have 30 fps, so any ms would have to be a multiple of 1/30 or ~0.033

Convert to mute WebM:
ffmpeg -i input.mp4 -c:v vp8 -crf 10 -b:v 1280k -an output.webm
>b:v parameter is the one to change, it's the quality of the video