CODEWITHSUNDEEP
h.264
K. Abdulla
K. Abdulla

Reputation: 11

validation of single h264 AVC nal unit

I have extracted several nal units from hard disk. I want to know which of them is valid nal unit or not. Is there any tool or code that can validate the structure or syntax of single h264 AVC nal unit.

Upvotes: 1

Views: 1186

Answers (1)

Alan M
Alan M

Reputation: 304

It depends. First you need to figure out what the NAL type is by the first byte. If the NAL is an SPS or PPS you can basically decode that as-is and see if the result is sane.

If the NAL is an actual coded slice, you will need at least three NALs to decode it. The corresponding SPS, PPS and the coded slice. You can decode the first few elements of the slice header without the SPS and PPS, but then you would need the corresponding SPS and PPS based on the PPS ID in the slice header to continue.

There were some command line tools (maybe h264_parse) that would dump this type of header information for you, or you can hack the reference decoder to help you out. http://iphome.hhi.de/suehring/tml/

In the end the only way to know if your NAL is "good" is to either match it up with the bitstream you started out with or fully decode it and verify the resulting picture output as bit-exact.

Checking the NAL byte length and maybe a checksum or CRC of each NAL can be helpful too, but no such mechanism exists in the bitstream, you'd have to add that on.

Upvotes: 1

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