What VideoZ inspects
| Tool | Input | What you see |
|---|---|---|
| MP4 Boxes | .mp4, .mov, .m4v, .m4a | Full ISO BMFF box (atom) tree with field values and byte offsets, iTunes metadata tags, codec / resolution / bitrate / GOP, and playback diagnostics |
| HLS / M3U8 | Playlist URL | Master playlist variants (bandwidth, resolution, codecs), media segments and durations, encryption, live playlist refresh |
| FLV Tags | .flv | FLV header, every audio / video / script tag with timestamp, size and offset, video codec and keyframes, onMetaData values |
Diagnostics for common video problems
When you drop an MP4 or MOV, VideoZ runs four checks directly on the file bytes, with no decoding needed:
- File integrity — detects truncated files and a missing moov box (“moov atom not found”).
- Faststart — whether moov comes before mdat, so web playback can start before the download finishes.
- iPhone / Safari compatibility — HEVC hev1 vs hvc1 tag, H.264 profile and level, interlacing and audio codec.
- Frame rate — constant vs variable frame rate, measured from every frame’s duration.
How it works
MP4 parsing uses mp4box.js plus a raw byte parser for boxes it skips (such as iTunes ilst tags). Codec, bitrate and GOP come from FFmpeg compiled to WebAssembly. FLV parsing is plain TypeScript. Everything runs in your browser tab, so there is no upload queue, no account and no file-size quota beyond your device’s memory (FFmpeg-based media info is limited to 500 MB).
Frequently asked questions
- Are my video files uploaded?
- No. MP4 and FLV files are read and parsed inside your browser tab with JavaScript and WebAssembly; the file never leaves your device. The only thing that goes through the VideoZ server is an HLS playlist URL, which is fetched by a small proxy because browsers block cross-origin playlist requests.
- Is VideoZ free?
- Yes. VideoZ is free to use, with no account, sign-up or watermark.
- Which formats are supported?
- MP4 and other ISO Base Media files (MOV, M4V, M4A, fragmented MP4), FLV files, and HLS playlists (.m3u8) by URL.
- How is this different from MediaInfo or ffprobe?
- MediaInfo and ffprobe are desktop and command-line tools. VideoZ runs in the browser with nothing to install, shows the raw MP4 box tree with byte offsets, and explains problems in plain language with the command to fix them.