Protocol scope and method
The scanner looks for three- and four-byte Annex-B start codes. It does not decode the bitstream payload.
NAL type = firstByteAfterStartCode & 0x1f.
Diagnostic scenario
Use a redacted Annex-B elementary-stream sample after transport and PS extraction. Scan start codes, identify SPS, PPS, IDR and slice units, and compare offsets with the demultiplexer log. Preserve the original byte sequence when diagnosing missing parameter sets.
How to interpret the result
NAL type identifies the unit class but does not validate RBSP syntax, decode order or picture integrity. Length-prefixed AVC samples do not contain Annex-B start codes and must not be scanned with this boundary rule without conversion.
Input reference
- Annex-B H.264 hex
- Example default: Sample input included
Common mistakes
- Using an unredacted production capture with vehicle, credential or network identifiers.
- Scanning length-prefixed AVC data as Annex-B.
- Treating a successfully parsed sample as standards compliance or interoperability proof.
Before using the result
- Confirm the protocol edition, transport framing and vendor profile before interpreting fields.
- Confirm stream format and inspect SPS/PPS presence before decoding.
- Keep a redacted known-good and known-bad sample as a regression pair.
Questions to check during diagnosis
Does the H.264 NAL Unit Scanner leave my browser?
No application upload is used. Avoid putting sensitive production data in shareable URLs.
Is this a standards compliance test?
No. Confirm the edition and vendor profile with licensed documents and your target platform.
Offline diagnostic aid. Verify fields, version and vendor extensions before production use.