How is the codec detected?

For MP4 and MOV files the tool walks the ISO BMFF box tree (moov → trak → mdia → minf → stbl → stsd) and reads the sample-entry fourCCs such as avc1 (H.264), hev1 (H.265), or mp4a (AAC), then maps them to readable names.

How is the frame rate measured?

Where the browser supports requestVideoFrameCallback, the tool plays a few frames muted and divides the frame count by the elapsed media time to estimate frames per second. It is an estimate and may be marked n/a in unsupported browsers.

Why are codecs not shown for some files?

Codec parsing relies on the MP4/MOV box format. WebM, MKV, and fragmented MP4s use a different structure, so the basic resolution and duration still appear but the codec list may be empty.

Is my video uploaded?

No. Only the first few megabytes of header bytes are read with DataView, and the file is opened via a local object URL. Nothing is sent to a server.

What is the container brand?

It is the major brand from the MP4 ftyp box — a four-character code like isom, mp42, or qt that signals which specification the file follows. It helps identify how the file was produced.

Video File Metadata Viewer

Inspect a video’s technical details in the browser

A metadata viewer tells you the resolution, duration, frame rate, container, and codecs of a video file — the facts you need before editing, transcoding, or uploading somewhere with strict requirements. This tool reads all of it locally, so the file never leaves your machine.

How it works

Two complementary sources are combined. First, the file is opened in a hidden HTML5 <video> element; its loadedmetadata event exposes duration, videoWidth, and videoHeight, and requestVideoFrameCallback (where available) is used to estimate the frame rate by counting rendered frames over a short span of media time.

Second, the first few megabytes of bytes are parsed as ISO Base Media File Format boxes with a DataView. The scan reads the major brand from the ftyp box, the timescale and duration from mvhd inside moov, and the codec fourCCs from each stsd sample entry. Those fourCCs — avc1, hev1, mp4a, and so on — are mapped to human-readable codec names.

Tips and notes

MP4 and MOV give the fullest report; WebM and MKV still show resolution and duration but may not list codecs because they use a different container format.
The frame rate is an estimate. For variable-frame-rate footage it reflects the playback average rather than a fixed value.
Container duration (from mvhd) and playback duration (from the video element) usually match; a mismatch can indicate edit lists or fragmented files.
Only header bytes are read, so even very large files are inspected quickly without loading the whole thing.