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, box structure, tracks, codecs, duration, average frame rate and approximate bitrate from bounded local slices without uploading media bytes.
Ready. Your working data stays in this browser.
Files 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. It reads hdlr, mdhd, stsd, stts and stsz metadata to report streams without decoding audio or video samples.
Practical example
Choose an MP4 and confirm its major brand, compatible brands, moov/mdat presence, track codecs, frame rate, bitrate estimate and structural warnings before reuse.
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.