"The file has no audio or video streams"

An MP4 or MOV keeps its picture and sound in an mdat box and describes them in a moov atom — the index that lists each track, its codec, and where every frame lives. Premiere's importer reads the moov first. If that index is missing or truncated — an unfinalized phone recording, an OBS or screen capture that crashed before writing the index, a download that was cut short — Premiere opens the file, finds no track table, and reports "The file has no audio or video streams." The frames are sitting in the mdat; Premiere simply has no map to them, which is why the same clip may still limp along in VLC (which scans more aggressively) while Premiere refuses it flatly.

"Codec missing or unsupported" is a different failure. Here the container is readable and the track table is present, but the codec inside isn't something Premiere's decoders will take: certain 10-bit or 4:2:2 HEVC variants, unusual H.264 profiles, or — the classic one — variable frame rate (VFR) footage from screen recorders and phones, which Premiere handles poorly. That is not a container problem, so a rebuild alone won't cure it; the answer is to transcode to a fixed-frame-rate mezzanine codec such as ProRes or DNxHR/DNxHD before importing.

Sorting the two apart tells you what to do. If the clip plays somewhere — a phone, VLC, a browser preview — but Premiere says "The file has no audio or video streams," you almost certainly have container/index damage. Common origins: a recording the camera or app never finalized (so the moov was never written), a file truncated by an interrupted transfer or a full disk, or offsets that point to the wrong place after a botched copy. Rebuilding the container reconstructs the sample tables Premiere reads, and the tracks reappear.

If instead the clip opens in Premiere's browser but errors on decode, or you see "Codec missing or unsupported," the container is fine and the codec or its parameters are the obstacle. Rebuild won't help there. The reliable path is to conform the file to an edit-friendly codec — export or transcode to ProRes, DNxHR or DNxHD at a constant frame rate — which also fixes VFR sync drift. Some people also clear the Media Cache and re-import; that only helps when Premiere cached a bad index of an otherwise-good file.

For the container case — the one behind "The file has no audio or video streams" — the tool scans the surviving H.264 or HEVC stream, rebuilds the moov index and sample tables, and writes a clean, seekable MP4/MOV that Premiere imports normally. Where the file was truncated, it salvages the frames written before the cut and closes a valid container around them, so a partly-transferred clip still imports the footage that made it rather than being rejected whole. All of this happens in your browser tab as the file is read from disk.

The honest limits: a rebuild cannot make Premiere decode a codec it doesn't support — if the underlying issue is an exotic HEVC profile or VFR, you'll still need to transcode after repair. And no tool can restore frames that were never written, so footage lost after an interruption stays lost. What the repair does guarantee is privacy: raw footage — often client work, unreleased material, or personal video — is read from disk and rebuilt locally, and you can watch the Network tab and confirm 0 bytes ever leave your machine.