Video Formats Explained: MP4, MOV, WebM, MKV and AVI

By the Everytoool team · 10 September 2026 · 4 min read

Containers, codecs, resolution and bitrate in plain language: and which video format to choose for phones, websites, editing and sharing.

“Why won’t this video play?” is one of the most common tech questions in any office or family. The answer is almost always the format. Video files are more complex than images or documents, but once you understand two concepts (containers and codecs) the confusion disappears.

Containers and codecs

A video file is like a box with several items inside. The container is the box: it defines the file extension (.mp4.mov.mkv.webm.avi) and holds the video track, audio tracks, subtitles and metadata together. The codecs are how each item inside the box is compressed:

• Video codecs: H.264 (AVC), H.265 (HEVC), VP8, VP9, AV1, MPEG4 Part 2.
• Audio codecs: AAC, MP3, Opus, Vorbis, AC3.

A device must support both the container and the codecs to play a file. That is why two files with the same .mp4 extension can behave differently: one might use H.264 (plays everywhere) and the other HEVC (needs newer hardware or software).

The common formats

MP4

MP4 is the universal choice. With H.264 video and AAC audio it plays on almost every phone, computer, browser, smart TV and social network. If you are unsure which format to use, choose MP4 (H.264).

MOV

Apple created MOV for QuickTime, and it is the format iPhones and Macs record in. Inside, it is very similar to MP4 and often contains the same codecs. Many Windows PCs and websites play MOV poorly, so converting to MP4 is a common need. Because the contents are often identical, MOV to MP4 can usually repackage the file in seconds without any quality loss.

WebM

WebM is an open, royalty free format designed for the web, using VP8, VP9 or AV1 video with Vorbis or Opus audio. Browsers support it well, and it is common for screen recordings made in the browser. Some editing software and Apple devices handle it less smoothly.

MKV

Matroska (MKV) is a flexible container that can hold many audio tracks, subtitle tracks and chapters. It is popular for archiving and media servers, but not ideal for sharing with everyday people.

AVI

AVI is an older Microsoft format. It is still required by some older TVs, car systems and legacy software, but files are usually larger and less efficient than MP4.

Resolution, frame rate and bitrate

Resolution

Resolution is the number of pixels in each frame: 720p (1280 × 720), 1080p (1920 × 1080), 4K (3840 × 2160). Each step up roughly doubles or quadruples the number of pixels, and therefore the data needed. For phones and messaging, 720p is usually plenty.

Frame rate

Measured in frames per second (fps). 24 to 30 fps is standard for most video; 60 fps makes fast motion smoother but increases file size.

Bitrate

Bitrate is the amount of data used per second of video. It is the biggest factor in file size. Phones record at high bitrates (often 15 to 50 Mbps) to preserve detail. Rebuilding at a sensible bitrate with an efficient codec can reduce size by 50 to 90% with little visible difference, which is exactly what a video compressor does.

Which format should you use?

Lossless repackaging versus rebuilding

If a video already uses compatible codecs, converting the container is quick and lossless. The data is copied into a new box. If the codecs are incompatible, the video must be rebuilt: every frame is decoded and compressed again. Rebuilding takes longer and can reduce quality slightly, but it is the only way to change codecs, resolution or bitrate.

Everytoool’s MP4 Converter automatically tries the fast, lossless route first and rebuilds only when needed.

Converting privately in your browser

Most online video converters upload your video to a server, which is slow for large files and risky for personal recordings. Everytoool uses FFmpeg compiled to WebAssembly, so conversion happens on your own device. The video never leaves your computer or phone.

Troubleshooting playback problems

• Video plays but no sound: the audio codec is unsupported. Convert to MP4 with AAC.
• Black screen with sound: the video codec (often HEVC) is unsupported. Convert to H.264.
• Video is sideways: rotate it in your phone’s gallery before converting.
• File too large to send: compress or lower the resolution.

With MP4 as your default and a basic understanding of containers and codecs, “this video won’t play” becomes a two minute fix rather than a mystery.