MP4, WebM, MP3 or M4A? Choosing the Right Format and Quality
What the format labels actually mean, why a 4K file is eight times the size of 1080p, and which option to pick for phones, editing and archiving.
Every downloader hands you a list of formats and resolutions with no explanation. Here is what the labels mean and how to choose without guessing.
Container vs codec
MP4, WebM and MKV are containers — wrappers that hold a video track, an audio track and metadata. H.264, VP9 and AV1 are codecs — the actual compression used inside. Two files both labelled "MP4" can behave very differently depending on the codec inside them.
- MP4 / H.264 — plays on essentially everything made in the last fifteen years: phones, smart TVs, editing software, PowerPoint. Largest file for a given quality, but the safest choice.
- WebM / VP9 — roughly 30% smaller than H.264 at the same quality. Plays fine in browsers and on modern Android, but older TVs and some editors reject it.
- MP4 / AV1 — smallest of the three, newest, and the most likely to stutter on hardware without an AV1 decoder.
Rule of thumb: if the file leaves your computer — a TV, a client, a video editor — choose MP4/H.264. If it stays in a browser and storage matters, WebM is a free win.
Audio: MP3 or M4A?
M4A (AAC) sounds better than MP3 at the same bitrate and is what the source video almost always already contains, so extracting to M4A avoids a second lossy re-encode. MP3 wins only on compatibility: car stereos, older MP3 players, some DJ software and a few car head units still expect it.
- 128 kbps — speech, podcasts, lectures. Small files, perfectly clear voices.
- 192 kbps — the sensible default for music on phone speakers or earbuds.
- 320 kbps — worth it only over decent headphones, and only when the source itself is high quality. A 128 kbps source re-encoded to 320 does not gain any detail; it just gets bigger.
Resolution and what it costs you
File size scales with the pixel count, so each step up is not a small increase. Approximate sizes for a ten-minute video at typical bitrates:
| Resolution | ~Size (10 min) | Best for |
|---|---|---|
| 360p | 25 MB | Slow connections, talking-head clips |
| 720p HD | 90 MB | Phones and tablets — the sweet spot |
| 1080p Full HD | 170 MB | Laptops, TVs, general archiving |
| 1440p | 350 MB | Large monitors, detailed screen recordings |
| 2160p 4K | 800 MB+ | 4K displays, footage you will edit or crop |
Two things worth knowing. First, a 4K option only appears if the creator uploaded in 4K — no downloader can invent detail that was never there. Second, on a phone screen the difference between 1080p and 4K is invisible while the file is five times larger.
Why high-resolution downloads take longer
Above 1080p, YouTube stores video and audio as separate streams. Any tool that gives you a single playable file has to download both and merge them — that is the pause you see before a 4K file appears. It is normal, and it is why a 4K download is not simply four times slower than 1080p.
Picking in five seconds
- Watching on a phone later → MP4, 720p
- Saving to a TV or NAS → MP4, 1080p
- Editing or re-framing → highest available MP4
- Just the audio, for a podcast → M4A or MP3, 128 kbps
- Music you actually listen to → MP3, 192 kbps or higher