Start with the destination requirements
A learning platform may have a maximum upload size while a presentation needs readable slides. Check the target's accepted file extension, size limit and preferred codec before compressing. Compressing to the smallest possible file is not always the right objective.
Bitrate and content complexity
Bitrate is one of the main controls over file size. Fast motion, low-light noise and screen recordings with fine text can show visible artifacts at aggressive settings. A static webcam shot may tolerate lower bitrate than a screen recording of a spreadsheet.
Evaluate a short representative sample
Choose a segment containing the most demanding content—small text, quick motion and voice audio. Compress it with moderate settings and listen for sync problems. If the sample looks acceptable, then process the full video.
Keep the original and check the export
Browser media processing can strain memory and CPU, particularly on mobile devices. Always retain the source until the exported file plays from start to finish on the target device. MP4 and MOV are containers and can hold different codecs.