What the format list on a downloader actually means — containers versus codecs, why file size varies so much at the same resolution, and how to choose the right one.
Ask a downloader for the available formats and you get a list of resolutions, extensions and sizes that seems to contain contradictions — two rows at the same resolution with very different sizes, one MP4 and one WebM. None of it is arbitrary. Here is what each column means.
Container versus codec
The extension — .mp4, .webm, .mkv — names the container. A container is a wrapper that holds the video stream, the audio stream, subtitles and metadata, and keeps them in sync. It says very little about quality.
The codec is what actually compresses the picture, and it lives inside the container. H.264, VP9 and AV1 are codecs. Two files at the same resolution with different codecs can differ in size by half, because a newer codec achieves the same visual quality with fewer bits.
| Codec | Usually inside | Efficiency | Compatibility |
|---|---|---|---|
| H.264 (AVC) | MP4 | Baseline | Plays on essentially everything |
| VP9 | WebM | ~30% better than H.264 | All modern browsers; some older TVs and editors struggle |
| AV1 | WebM / MP4 | ~30% better than VP9 | Recent devices only; decoding is demanding on old hardware |
Which should you pick?
- Choose MP4/H.264 when the file has to simply work — sending to someone else, playing on a TV, importing into older editing software.
- Choose WebM/VP9 or AV1 when you want the smallest file at a given quality and you know the device is recent.
- When in doubt, MP4. The size penalty is real but modest; a file that will not play is a total loss.
Why resolution alone tells you little
Resolution is the pixel count — 1920×1080 for Full HD. Bitrate is how many bits per second are spent describing those pixels, and it is bitrate that determines whether the picture holds together in motion. A 1080p file at a low bitrate will fall apart into blocks during fast movement, while a 720p file at a healthy bitrate stays clean. This is why an upscaled video never looks better than its source: adding pixels without adding information adds nothing.
Video-only streams
Some rows have no audio at all. Platforms store higher resolutions as separate video and audio streams, so the raw video stream exists on its own. Downloading it gives you a silent file. That is occasionally what you want as an editing source, and almost never what you want for watching — which is why the standard Download option fetches both and merges them for you.
About this article. Written and reviewed in-house by the All-in-One Video Download team at Parv Gupta. It is not sponsored, contains no paid links, and no advertiser had any input into it. Spotted an error? Tell us at support@allinonevideodownload.com and we will correct it.
General information only — not legal advice. See our Disclaimer.