CloudConverterYou save a YouTube video, double-click it, and Windows says it can't play the file. Or your editor refuses it. Or it plays, but with no sound. Nine times out of ten the problem isn't the video, it's the format it was saved in.
YouTube doesn't actually store your favourite video as one MP4. It keeps several versions in different formats and serves whichever suits your browser. Download tools grab one of those, and that's how you end up with a WebM, an MKV or a silent MP4. Here's what each one is, which you should keep, and how to fix the ones you already have.
What YouTube really sends you
Behind every video there are separate video streams and audio streams:
- Video: H.264 (in MP4), VP9 (in WebM) and, for newer uploads, AV1.
- Audio: AAC (in MP4/M4A) or Opus (in WebM).
At 1080p and above, picture and sound almost always come as two separate files. A good downloader merges them into one file. A lazy one gives you just the picture, which is why some "1080p downloads" are silent.
MP4 vs WebM vs MKV at a glance
| MP4 | WebM | MKV | |
|---|---|---|---|
| Typical codecs | H.264 + AAC | VP9 / AV1 + Opus | Anything |
| Plays on iPhone / Photos app | Yes | Often not | No |
| Plays in Windows Media Player / TV | Yes | Sometimes | Sometimes |
| Opens in CapCut, Premiere, iMovie | Yes | Rarely | Rarely |
| Share on WhatsApp / social media | Yes | Usually converted or rejected | Rejected |
| File size at the same quality | Medium | Smaller | Depends on contents |
WebM is efficient and great for streaming, and MKV is a flexible container that hobbyists love. But if you want a file that simply works everywhere, MP4 with H.264 and AAC is still the safe choice.
The easy route: download it as MP4 from the start
The cleanest file is the one you never have to convert. Use a YouTube to MP4 converter that hands you a single MP4 with the sound already merged in. YTMP4, for example, lists every quality from 1080p down to 144p, plus MP3 and M4A if you only want the audio. No re-encoding means no quality loss.
A few tips while you're there:
- Pick 720p for phones. It looks sharp on a 6-inch screen at roughly half the size of 1080p.
- Pick 1080p for laptops, TVs and anything you'll edit.
- Check the file plays with sound before you delete anything from your phone.
Already have a WebM or MKV? Convert it
If the file is already on your computer, there's no need to download it again:
- Open WebM to MP4 or MKV to MP4.
- Drop the file in and start the conversion.
- Download the MP4 and check the sound.
This step re-encodes the video, so it takes longer than a download and the file can come out slightly bigger than the WebM. That's normal: H.264 needs a bit more data than VP9 for the same picture.
Quick fixes for common problems
Video plays but there's no sound. You have a video-only stream. Download again with a tool that merges the audio, or pick a lower quality, which YouTube often stores with sound included.
Plays on PC but not on iPhone. It's probably WebM or VP9. Convert it to MP4 (H.264).
The file is huge. A 20-minute 1080p video can pass 400 MB. Re-download at 720p, or convert with a lower resolution setting.
The editor shows a black screen. The clip is likely AV1 or VP9. Convert it to H.264 MP4 and import it again.
One last thing
Only save videos you own, ones the creator lets you download, or content that's free to reuse. Format tricks don't change copyright: re-uploading someone else's video is still a problem, whatever the file extension.
Short version: if you're saving from YouTube, ask for MP4 straight away. If you already have something else, convert it once, and you'll never see "can't play this file" again.