About the youtube playlist to mp4
MP4 is the right call whenever the screen carries meaning. Tutorials with on-screen code, lectures with slides, dance and technique videos, film analysis, anything where pausing on a frame is part of watching it. For everything else, audio-only saves a large multiple of the storage.
Quality is capped by the upload, not by the tool. If a channel published in 720p, 720p is the ceiling — upscaling would invent detail rather than recover it. For most study material 720p is the sweet spot: text stays readable, files stay manageable, and playback is smooth on any laptop or tablet.
Storage adds up faster than people plan for. As a rough guide, an hour of 720p is around 0.5 GB, 1080p around 1–1.5 GB, and 4K comfortably 5 GB or more. A hundred-video HD course can therefore reach 15–20 GB, which is worth checking before you start rather than halfway through.
Container and codec choices matter for older hardware. MP4 with H.264 is the safest possible pairing and plays on essentially every phone, TV and car screen made in the last decade. WebM with VP9 is smaller at the same quality but fails on some older devices, so prefer it only when you know your playback target.
For long series, plan the folder structure before the first file lands: one folder per playlist, a two-digit index prefix on every filename, and a plain-text note with the source URL and date. It costs a minute now and saves an hour when you come back to the archive months later.