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.

What is the Video File Metadata Viewer?

Read resolution, duration, and an estimated frame rate from the HTML5 video element, plus container brand and codec fourCCs by scanning the MP4/MOV ISO BMFF box structure with DataView. No upload — everything is parsed in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Video File Metadata Viewer

Name: Video File Metadata Viewer
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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.

Why you would need to check video metadata

Knowing a file’s codec and resolution before doing anything with it prevents a range of common problems:

Before uploading to a platform. YouTube, Vimeo, TikTok, and most social platforms accept only certain codec and container combinations. Uploading a video in an unsupported format results in transcoding failures or silent quality degradation. Checking that your export is H.264 in an MP4 container before uploading avoids that.

Before editing in a timeline. Some video editing applications handle H.264 or H.265 natively; others need proxy files or re-encoding. Knowing the codec first lets you decide whether to ingest directly or create proxies to avoid dropped frames during editing.

Before AI video upscaling. Tools like Topaz Video AI or Real-ESRGAN need to know the source resolution and codec to apply the right model and scale factor. Confirming the exact resolution (for example 512×896 from a portrait-mode AI generation) lets you target the correct upscaling multiplier.

For debugging playback issues. If a video plays on one device but not another, the codec is often the cause. A HEVC (H.265) file plays fine in VLC but may not play in older browser-based players that only support H.264. Reading the codec from the file confirms the cause without needing to guess.

What each metadata field means

Field	What it tells you
Resolution	Width × height in pixels; determines aspect ratio and display sharpness
Duration	Total length in seconds, as reported by the container
Frame rate	Frames per second, estimated from playback (see note below)
File size	Total bytes; with duration gives you a rough sense of effective bitrate
Container brand	The ftyp major brand — for example `isom` (generic MP4), `mp42`, or `qt` (QuickTime)
Video codec fourCC	`avc1` = H.264, `hev1`/`hvc1` = H.265, `av01` = AV1, `vp09` = VP9
Audio codec fourCC	`mp4a` = AAC, `ac-3` = Dolby, `Opus` = Opus

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 derived from actual decoded frames during playback. For variable-frame-rate footage it reflects the playback average rather than a fixed editorial value. If you need exact FPS, use a dedicated tool like ffprobe on the command line.
Container duration (from mvhd) and playback duration (from the video element) usually match; a meaningful mismatch can indicate edit lists, fragmented MP4 packaging, or a corrupted file.
Only the first few megabytes of header bytes are read via DataView, so even very large files are inspected quickly without loading the whole video into memory. For a multi-gigabyte 4K file, the check typically completes in under a second.