Tesla SEI Forensic Decoder

The raw MP4 file was read byte by byte. The tool searched for the Tesla SEI telemetry marker — the byte sequence 42 42 42 69 08 — which appears once per video frame. This is a direct binary scan, not a container-navigation approach. Tesla publish their own open-source extractor at github.com/teslamotors/dashcam which walks the MP4 container structure using NAL length prefixes to locate SEI units. This tool was built independently and blind to that script — the UUID pattern, RBSP decode logic and protobuf field mapping were derived directly from the binary. The two approaches were compared after the fact and produce identical decoded values. The difference is that container navigation depends on the MP4 length prefix structure being intact — if a NAL length value is corrupt or unexpected, the container walk moves on and that frame is lost. A raw binary scan finds the SEI payload regardless of container integrity, which is why this tool may recover frames that the Tesla extractor and SEI player export miss. Learn about SEI telemetry →

H.264 video uses a mechanism called emulation prevention to avoid certain byte sequences being mistaken for video structure markers. Any 00 00 03 byte triplet has the 03 byte removed before reading. This gives the true payload bytes. The hex dump shows both the raw bytes and the decoded bytes so either can be independently verified.

Tesla encodes telemetry using Google's protobuf format — a compact way of labelling and storing data fields. Each field has a tag number that identifies what it contains. Field 3 is the frame sequence number. Field 4 is vehicle speed in m/s. Field 6 is steering angle in degrees, and so on. The tool reads each tag and extracts the value directly.

The SHA-256 hash is a mathematical fingerprint of the entire file contents. If a single byte in the file changes — deliberately or by corruption — the hash will be completely different. Comparing this hash with the hash of the original exhibit confirms the file analysed here is identical to the file in the chain of custody.

Each SEI unit carries a frame sequence number that increments by 1 per frame. If the decoded sequence jumps — for example from frame 45,210 to frame 45,215 — then frames 45,211 through 45,214 are absent from the binary. This tool reports every such gap so they can be investigated and distinguished from omissions in a CSV export versus genuine data absence in the recording.