Drop in an MP4, MOV, AVI, MKV, or WebM file. MP4/MOV get a real ISOBMFF box walk — including the classic "recording got interrupted" problem where mdat (the actual video data) exists but moov (the index describing how to play it) never got written. AVI gets a RIFF chunk walk, MKV/WebM an EBML element walk. All three check declared sizes against what's actually in the file.
If you're here because something threw one of these, this tool shows you exactly what's wrong and how much is recoverable:
This inspects container structure, not the compressed video/audio payload — it can't decode a frame or tell you the video will actually play smoothly, only whether the container's own declared structure is intact. It can't fix a missing moov box (rebuilding one from raw mdat samples requires re-deriving the entire sample table, which needs a real muxer, not a browser tab), only diagnose that this is the problem. MP4/MOV: only moov is walked one level into trak boxes for track ID/duration/dimensions — the full sample-to-chunk tables inside stbl aren't parsed. AVI: only the top-level RIFF/LIST structure is walked, not the individual frame index in detail. MKV/WebM: only the top-level EBML elements and Segment's immediate children are enumerated — Cluster contents (actual frame data) aren't parsed, and an EBML element with "unknown size" (legitimate in streamed/piped Matroska files) is reported as such, not treated as an error. No codec-level (H.264/H.265/VP9/AV1/etc.) validation of any kind.