Ffmpeg

ffmpeg -i <input>.mp4 <output>.webm

ffmpeg -i MVI_0083.MP4 -s 960x540 -crf 18 20190322_out.webm
ffmpeg -i MVI_0083.MP4 -s 960x540 20190322_out.mp4
ffmpeg.exe -i "test.avi" -c:v libx264 -crf 20 -c:a aac -strict -2 "test.mp4"

You might want to use the -ss and -t options to create short test encodes. -ss being the start time and -t being the duration — both in seconds. You probably don’t need to encode the entire video to determine what’s acceptable.

crf

• 0 = lossless
• 18 = visually lossless
• 23 = default
• 28 = sane low quality
• 51 = worst quality possible
• The range is exponential, so increasing the CRF value +6 results in roughly half the bitrate / file size, while -6 leads to roughly twice the bitrate.

Common Video Screen Sizes

• screens

• 960x540 horizontal (540x960 vertical)
• 640x360
• 512x288 (288x512)
• 340x202

• 360x240 3:2
• 720x480 3:2