What is a .mp4 file?
video/mp4
MP4 (MPEG-4 Part 14) is the dominant container for digital video, holding video, audio, subtitle, and metadata tracks in a tree of typed boxes. `ftyp` declares the brand, `moov` carries the sample tables that make seeking possible, and `mdat` holds the media; when an encoder writes `moov` last, playback cannot begin until the file has fully downloaded, which a faststart remux fixes. It derives from Apple's QuickTime format, generalized by ISO into the ISOBMFF base that MOV, 3GP, and HEIF share.
How to use a .mp4 file
Use an example MP4 to test box parsing and track detection, seeking, range-request streaming, and transcode or thumbnail pipelines — verifying that a file with a trailing `moov` box is still handled, and that codec support is checked per track rather than inferred from the extension.
Download example .mp4 files
- MP4 — H.264 ClipA short H.264 test clip in an MP4 container (yuv420p, faststart) — the most widely supported web and mobile video format. Video-only and tiny; for testing players, thumbnailers, and MP4→other conversion.
- A/V Sync — Beep + Flash (MP4, with audio)A five-second clip that flashes white and plays a 1 kHz beep on every whole second — the first clip in the library WITH an audio track. A direct fixture for measuring and correcting audio/video sync (lip-sync) offset.
- SMPTE Colour Bars + 1 kHz Tone (MP4)Standard SMPTE-style colour bars with a 1 kHz reference tone — the classic broadcast test pattern. A fixture for calibrating colour, testing decoders, and verifying audio alongside a known video signal.
- Countdown with Timecode (MP4)A six-second countdown (5→0) with a sweeping second-arc, a burned-in SS:FF timecode, and a beep on each second — a slate/leader fixture for testing timecode reading, frame-accurate seeking, and sync.
- Vertical 9:16 Clip (MP4, 270x480)A portrait 9:16 (270×480) clip with a vertically-moving marker — the aspect ratio of phone and short-form video. A fixture for testing vertical-video handling, orientation, and letterboxing in players and thumbnailers.
- 60 fps Clip (MP4)A 60 frames-per-second clip with a smoothly sweeping marker — double the usual frame rate. A fixture for testing high-frame-rate playback, frame-rate detection, and fps conversion (60→30 decimation).
- Soft Subtitles — MP4 (mov_text track)The same clip with a soft subtitle track as MP4 mov_text (the MP4-native subtitle format) — the format twin of the MKV/SRT file, for testing subtitle handling across containers.
- Terminal Screencast Mock (MP4)A screen-recording-style clip of a mock terminal — a window with traffic-light buttons and build output typing out line by line with a blinking cursor. A fixture for testing screen-capture pipelines, UI-motion thumbnails, and text-in-video OCR.
and 374 more in the library.