Why this tool is useful
Verify that an MP4 contains its expected container header, movie metadata and media box before transfer, while keeping large media bytes on the device.
Local File Tools · runs locally
Private MP4 Container Inspector
Inspect MP4 brands, top-level box structure and declared track handlers from bounded local file slices without decoding or uploading the media payload.
Ready. Your working data stays in this browser.
Files and capture streams stay on this device. Processing uses browser APIs only; nothing is uploaded to YTSave, the media API or a proxy.
How it works
The browser walks ISO Base Media box headers with small File.slice reads, skips mdat payload bytes, and opens only a bounded moov box to identify nested track handlers.
Practical example
Choose an MP4 and confirm its major brand, compatible brands, moov/mdat presence, track types and structural warnings before using the file elsewhere.
Validation
The calculation is deterministic and explains validation errors instead of silently changing invalid input.
Privacy boundary
Input and output remain in this tab. Copy and download happen through browser APIs without a server upload.
Result passport
Every run reports its tool mode, timestamp and input/output size so transformed data can be audited.