MP4 vs WebM: Which Video Format Should You Use?

The codecs inside each container are what truly determine video quality and file size. Understanding these codecs is essential to making an informed format choice.

H.264 (AVC) has been the dominant video codec for over a decade. It delivers excellent quality at moderate bitrates and enjoys universal hardware decoding support across phones, tablets, computers, smart TVs, and streaming devices. H.264's maturity means that encoders are highly optimized and produce consistent, predictable results. The downside is that H.264 is encumbered by patents held by the MPEG LA consortium, which means commercial use technically requires licensing fees, though these fees rarely affect individual users or small businesses.

H.265 (HEVC) is the successor to H.264 and offers roughly 40-50 percent better compression at the same quality level. However, H.265 has a complex and fragmented patent landscape with multiple licensing pools, which has slowed its adoption. Browser support for H.265 in MP4 is growing but not yet universal.

VP9, Google's codec for WebM, was designed to compete directly with H.265. VP9 achieves comparable compression efficiency to H.265 while being completely royalty-free. YouTube uses VP9 extensively, which has driven widespread browser and device support. VP9 encoding is slower than H.264 encoding at comparable quality levels, but playback decoding is efficient and hardware-accelerated on most modern devices.

AV1 is the newest codec in this landscape, developed by the Alliance for Open Media (which includes Google, Mozilla, Microsoft, Apple, and others). AV1 can be used in both MP4 and WebM containers and offers roughly 30 percent better compression than VP9 or H.265. AV1 is royalty-free but still relatively new, so hardware decoding support is limited to the latest generation of devices and chips.

Browser compatibility is often the deciding factor when choosing between MP4 and WebM, especially for web developers building sites or applications that serve video.

MP4 with H.264 enjoys truly universal browser support. Every modern web browser, including Chrome, Firefox, Safari, Edge, and Opera, can play H.264 MP4 files natively. Safari was historically the notable holdout for WebM support, and while this has improved in recent versions, MP4 remains the only format guaranteed to work across all browsers without exception. Beyond browsers, MP4 plays on virtually every device ever made: smartphones, tablets, smart TVs, game consoles, car infotainment systems, and even most digital picture frames.

WebM support has grown substantially since its introduction but still has gaps. Chrome and Firefox have supported WebM since its launch. Edge added support when it switched to the Chromium engine. Safari added WebM VP9 support in macOS Big Sur (2020) and iOS 16 (2022), but older Apple devices and operating systems cannot play WebM natively. Hardware decoding for VP9 is available on most modern processors but is not as universally guaranteed as H.264 hardware decoding, which can affect battery life on mobile devices.

For web developers, the practical recommendation is to provide MP4 as a baseline and optionally serve WebM as a preferred source when browser support is detected. The HTML5 video element's multiple source capability makes this straightforward to implement.

File size is where the competition between MP4 and WebM gets interesting, because the answer depends heavily on which codecs you are comparing.

At equivalent quality levels, MP4 with H.264 and WebM with VP9 produce files of roughly similar size, though VP9 typically achieves a slight 10-20 percent advantage in compression efficiency. This means a 100 MB H.264 MP4 file could potentially be encoded as an 80-90 MB VP9 WebM file at the same visual quality. The savings become more pronounced at higher resolutions: VP9's advantage is more noticeable at 4K than at 720p.

If you compare H.265 MP4 against VP9 WebM, the two are extremely close in compression efficiency, with neither having a consistent advantage. Both achieve roughly 40-50 percent better compression than H.264.

AV1, which can be used in either container, outperforms all of the above by approximately 30 percent, but encoding speed is significantly slower, making it impractical for real-time or quick conversion scenarios.

For most practical purposes, the file size difference between MP4 (H.264) and WebM (VP9) is meaningful but not dramatic. If reducing file size is your primary concern and you are targeting modern browsers, WebM with VP9 offers a genuine advantage. If compatibility is paramount, the slightly larger H.264 MP4 is the safer choice.

Objective quality metrics like PSNR (Peak Signal-to-Noise Ratio) and SSIM (Structural Similarity Index) can be used to compare the visual quality of MP4 and WebM at equivalent bitrates.

At bitrates above 5 Mbps for 1080p content, H.264 and VP9 produce nearly indistinguishable results. The human eye cannot reliably tell them apart in side-by-side comparisons. At lower bitrates, where compression artifacts become more visible, VP9 generally handles detail preservation and motion rendering slightly better than H.264. This makes VP9 WebM a better choice for bandwidth-constrained scenarios, such as streaming to mobile users on cellular connections.

H.265 and VP9 are closely matched at all bitrates, trading wins depending on the type of content. Animation and screen recordings tend to favor VP9, while live-action footage with film grain sometimes favors H.265. The differences are marginal in most cases.

Subjectively, both formats produce excellent video quality when encoded with appropriate settings. The codec matters less than the encoding parameters: a well-encoded H.264 MP4 will look better than a poorly encoded VP9 WebM, and vice versa. The quality of the encoder implementation, the number of encoding passes, and the bitrate allocation strategy all have a larger impact on perceived quality than the choice of codec alone.

For archival or professional purposes, encoding at a high bitrate in either format will preserve quality effectively. For web distribution, the slight compression advantage of VP9 means you can deliver the same visual experience to your audience while using less bandwidth.

The right format depends on your specific use case, audience, and priorities.

Choose MP4 when you need universal compatibility. If your video will be viewed on a wide range of devices, shared via email or messaging apps, embedded in presentations, or played on smart TVs and other consumer electronics, MP4 with H.264 is the safest bet. It simply works everywhere. MP4 is also the preferred format for social media uploads, as platforms like Instagram, TikTok, Facebook, and LinkedIn all accept and recommend MP4.

Choose WebM when you are building for the web and want to optimize for performance. If you control the playback environment (your own website or web application), WebM with VP9 can deliver the same quality at a smaller file size, reducing bandwidth costs and improving load times. WebM is particularly well-suited for HTML5 video backgrounds, web-based video players, and progressive web applications. Since WebM is royalty-free, there are no licensing concerns for commercial use at any scale.

For the best of both worlds, serve both formats. Use the HTML5 video element to specify WebM as the preferred source with an MP4 fallback. Modern browsers will select WebM for its efficiency, while older or incompatible browsers will fall back to MP4. This dual-format approach is used by YouTube, Netflix, and most major streaming platforms.

If you need to convert between formats, tools like ConvertFree handle the conversion entirely in your browser. This means your video never gets uploaded to a third-party server, preserving your privacy while giving you access to both formats. The conversion process typically takes seconds for short videos and a few minutes for longer content.

Converting between MP4 and WebM is straightforward with the right tools. Here is what you need to know about the conversion process.

When converting MP4 to WebM, the video and audio streams must be re-encoded because the codecs are different. H.264 video will be re-encoded to VP8 or VP9, and AAC audio will be re-encoded to Vorbis or Opus. This means there is a generational quality loss, though it is minimal when using high-quality encoding settings. To minimize quality loss, use the highest practical bitrate and prefer VP9 over VP8 for better compression efficiency.

When converting WebM to MP4, the reverse applies: VP8 or VP9 video is re-encoded to H.264, and Vorbis or Opus audio is re-encoded to AAC. Again, use high-quality settings to minimize any perceptible quality difference.

ConvertFree makes this process simple and private. Because the conversion happens entirely in your browser using WebAssembly, your video files never leave your device. There are no file size limits imposed by server uploads, and you do not need to create an account or install any software. Simply select your source file, choose the target format, and let the browser handle the rest.

For batch conversions or professional workflows, desktop tools like FFmpeg offer more granular control over encoding parameters, but for most users, a browser-based converter provides the convenience and privacy that matters most.