MP4

MP4 (MPEG-4 Part 14) is a multimedia container format with the .mp4 extension. It packages compressed video, audio, and metadata, commonly H.264 or H.265 video with AAC audio.

Why it matters

MP4 plays in nearly every browser, phone, and TV, so it is the safe choice for uploading and streaming video. The container is not the codec: two MP4 files can use different codecs with different quality and compatibility. For web playback, placing metadata at the start of the file lets it start before the download completes.

Adaptive streaming services typically split video into small segments of several qualities.

Example

$ ffmpeg -i input.mov -c:v libx264 -crf 23 -c:a aac -movflags +faststart output.mp4

This converts a video to H.264 and AAC, and the faststart flag lets the browser begin playing early.

Common mistakes

• Assuming every MP4 plays everywhere; the codec inside matters.
• Skipping faststart, so playback waits for the full download.
• Serving huge video files directly when a streaming service or CDN fits better.

Related

• Codec
• Bitrate
• GIF (Graphics Interchange Format)
• Lossy vs Lossless Compression

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