What is the indication of corrupt NAL units in an H.264 stream?

How can I identify issues with IDR Pictures, which should be denoted by a nal_unit_type value of 5. Using sequences like 0x00 00 00 01 or 0x00 00 01, I’ve successfully located the beginning of NAL units and their corresponding headers, consisting of nal_ref_idc and nal_unit_type.

However, my attempts to find corrupt NAL units have been inconclusive. I’ve come across headers with values such as 67, 68, 01, 41, but none seem to indicate corruption.

Despite researching extensively, I haven’t found examples of corrupt NAL units. Could there be a misunderstanding on my part regarding NAL unit behavior, or is there a specific header pattern associated with corruption? Any clarification or examples of corrupt NAL units would be greatly appreciated.

Hey Sahil!

Identifying corrupt NAL units within an H.264 stream is a challenge, requiring careful examination and understanding of the stream’s structure. In an H.264 stream, NAL units encapsulate the compressed video data, each commencing with a start code prefix typically denoted as 0x00 00 00 01 or 0x00 00 01. These start codes precede a header containing fields like nal_ref_idc and nal_unit_type, with the latter indicating the NAL unit’s type.

To detect corrupt NAL units, it’s crucial to discern the expected values for the nal_unit_type field. For instance, an IDR Picture, a keyframe in H.264 encoding, usually carries a nal_unit_type value of 5. However, deviations from this norm, such as the nal_unit_type values of 67, 68, 01, and 41 you’ve noted, may not necessarily imply corruption. The nal_unit_type values can vary based on the NAL unit’s purpose, like slice headers, sequence parameter sets, or picture parameter sets.

To ascertain whether these deviations indeed signify corruption or adhere to specific patterns, further analysis of the H.264 stream is necessary. Comparing the stream against H.264 standard specifications aids in validating the NAL units’ integrity. Seeking examples or case studies from literature, forums, or expert discussions can provide additional insights. Collaborating with peers or experts in video encoding and H.264 compression may also offer valuable guidance on addressing issues related to corrupt NAL units.