Can I use both formats at the same time?

Yes, and for publishing on a website this is actually the best approach. HTML's video element lets you define more than one source file; the browser tries the list in order and plays the first file it can open. If you put WEBM first and MP4 as the fallback, modern browsers pull the small file while older or more limited ones drop to MP4. The cost of this is hosting both files and running two separate encodes.

Does the file size difference genuinely matter?

That depends entirely on scale. For a promotional video watched by a few hundred people a month the difference is practically irrelevant; it is not worth the extra encoding effort. But if your site carries a lot of videos or your traffic is high, it can have a visible effect on bandwidth cost and page load time. For users watching on a mobile connection, a smaller file also means a faster start.

Will my file get even smaller if I use AV1?

AV1 was designed as VP9's successor and can generally carry the same visual quality with less data. However, encoding time is markedly longer and hardware decoding support is relatively recent. On older devices playback falls on the processor, which increases battery drain and can cause stuttering on weaker hardware. So AV1's size advantage is real, but it exacts a price on both the production and the viewing side.

WEBM or MP4? The Choice Between Compatibility and File Size

Q: Can I upload WEBM to social media?

The vast majority of platforms will not accept a WEBM upload or will not handle it reliably. Some reject the file, some accept it and convert it to their own format in the background, which means a quality loss outside your control. Uploading the video directly as MP4 both lets you see how the result will look and prevents surprise errors. Where social media is concerned, MP4 is unarguably the right choice.

Two good formats, two different priorities

There is no bad option in this debate. WEBM and MP4 are both formats that fulfil their design purpose well. The problem is that their design purposes differ, and that difference makes one right and the other wrong depending on where you are going to put your video.

WEBM was designed to play video efficiently inside a web browser. MP4 was designed to open wherever possible. That sentence is really the summary of the whole comparison — but the details matter, because "opening everywhere" and "being efficient" are both goals with a price attached.

The technical basis: both are containers, their contents differ

Both formats are containers — the outer layer that holds video, audio and timing information together. What determines quality and size is not the container but the codec inside it.

WEBM carries VP8, VP9 or AV1 video; Vorbis or Opus audio. All of these are open codecs with no licensing restrictions.

MP4 commonly carries H.264 or H.265 video; AAC audio.

This distinction is critical, because there is no codec in common between the two containers. Turning a WEBM into an MP4 is not an easy box swap like turning a MOV into an MP4. The data genuinely has to be decoded and recompressed.

Where WEBM is strong

File size. VP9 and AV1 come from newer compression generations than H.264. They carry the same visual quality with less data. When you prepare the same video in both formats, the WEBM version is usually markedly smaller.

Openness. WEBM is an open format with no patent licensing headaches. If you are developing software or building your own infrastructure, this is a practical advantage.

Transparency support. WEBM can carry an alpha channel, meaning video with a transparent background is possible. If you are going to use a logo animation or a graphic overlaid on an element in a web page, this alone can be decisive. MP4 does not commonly offer this.

Browser support. WEBM plays without trouble in modern browsers. There is no real obstacle to web publishing.

Where MP4 is strong

It opens everywhere. This is MP4's single biggest argument, but it is so strong that it is sufficient on its own in most scenarios. Phone galleries, smart televisions, tablet apps, messaging apps, editing programs, presentation software — all of them open MP4.

Social media expects it. The vast majority of platforms are built around MP4 uploads. WEBM is either rejected or converted in the background, which means a quality loss outside your control.

Hardware support. H.264 is decoded in hardware on almost every device's chip. This means playback is smooth and battery drain stays low. That support is narrower for VP9 and newer for AV1.

Encoding speed. Encoding with H.264 finishes far faster than encoding with VP9 or AV1. If you are processing a lot of videos, that difference amounts to a serious amount of time.

The direct trade-off: what are you giving up for what?

If you choose WEBM you gain a smaller file and the option of transparency, and in return you lose the world outside the browser. Encoding time also gets longer.

If you choose MP4 you gain universal compatibility and fast encoding, and in return you accept a larger file for the same quality and give up transparency.

If you convert — that is, turn the WEBM into an MP4 — you get the compatibility gain above but pay two additional costs. First, because re-encoding is mandatory, some quality loss occurs; with good settings that loss usually goes unnoticed, but it exists and cannot be undone. Second, your file will most likely get bigger, because H.264 needs more data to hold the same quality. Knowing both of these outcomes up front keeps the result from surprising you.

Decision framework: which one in which situation?

The video will only be published on your own site. Stay on WEBM. Browsers open it, the file is small, the page loads quickly. Better still, use the dual-source method described below.

The video will be uploaded to social media. MP4. Unarguably. Most platforms do not accept WEBM.

The video will be watched on a phone or a television. MP4. Gallery apps and televisions generally do not recognise WEBM.

The video will be imported into an editing program. MP4. Editing software's WEBM support is narrow and inconsistent.

The video has a transparent background. Stay on WEBM. If you move to MP4 the transparency is lost and the background usually turns black — this is not a bug, it is the limit of the format.

The video will be sent to someone by email or message. MP4. You cannot know what device the recipient will open it on; do not take the risk.

You are not sure. MP4. If you cannot answer "who will open this file, and where" clearly, compatibility is always the more valuable thing.

The best solution for a website: both at once

If you are publishing video on your own site you do not have to choose. HTML's video element lets you define more than one source. If you put WEBM first and MP4 second, every browser plays the first file it can open. Modern browsers pull the small WEBM, more limited ones drop to MP4.

The cost is preparing and hosting both files. For small sites this may not be worth the effort; on video-heavy or high-traffic sites the gain is real.

If you have a job on the conversion side, you can use our WEBM to MP4 converter; remember that the operation requires re-encoding and can take minutes on large files.

In summary

The choice between WEBM and MP4 is not a quality comparison but a question of audience. If your video is going to stay inside the browser, WEBM offers real advantages such as a smaller file and transparency. If your video is going to leave the browser — to a phone, a television, social media, an editing desk — MP4's universality leaves every other advantage behind. When deciding, ask yourself a single question: am I going to play this file, or is it going to a device I cannot control? If the answer is the latter, MP4 is the right address.