IT/Software/Command Line Applications/ffmpeg

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This tool is amazingly broad.

We will only attempt to show a few of its key features.

Reduce Video size and maintain some quality.

ffmpeg -i input.mp4 -vcodec libx264 -crf 20 output.mp4

crf should vary between 18 and 32. The higher the number the higher the compression and lower the quality

You can also reduce the audio bitrate -b:a 32k -crf 32 output32_23.mp4

Reduce Audio Size

This will take an mp3 or other audio file and shrink it.

I do not recommend going below 32k or the sound will have hiss.

ffmpeg -i The\ Scarlet\ Letter.mp3 -b:a 64k theScarletLetter64k.mp3

Convert a whole directory.

for i in *.avi; do ffmpeg -i "$i" "${i%.*}.mp4"; done

You can add your parameters there like crf and -vcodec

Extract audio from video

Change extension and names as needed.
Path is relative unless noted.
Single quotes are needed if you have spaces or any special character

ffmpeg -i '20150125 Word Blesses Us'.mp4 '20150125 Word Blesses Us'.mp3

Trim based on start and end time.

Try using this. It is the fastest and best ffmpeg-way I have figure it out:

 ffmpeg -i input.mp4 -ss 00:01:00 -to 00:02:00 -c copy output.mp4

This command trims your video in seconds!

Explanation of the command:

-i: This specifies the input file. In that case, it is (input.mp4).
-ss: Used with -i, this seeks(seek start) in the input file (input.mp4) to position.
00:01:00: This is the time your trimmed video will start with.
-to: This specifies(time out) duration from start (00:01:40) to end (00:02:12).
00:02:00: This is the time your trimmed video will end with.

-c copy: This is an option to trim via stream copy. (NB: Very fast)

I highly recommend Lossless Cut from github. It is very nice and easy to use and cross platform.