[Mp4-tech] Annex b format

[Venkat Subbiah]

Hi Muneeb,
Below is text of a response from Gary Sullivan to a similar query. Hopefully
this clears it's up for you.
Thx,
Venkat
See Annex B of the standard.  Start codes (0x000001) prefixed by at least
one zero-valued byte (i.e. a total length of 4 bytes in the pattern
0x00000001) are required between the last NAL unit of one access unit and
the first NAL unit of the next access unit.  Additional zero-valued bytes
may also be present.
Between NAL units within the access unit, the minimum number of bytes is 3
rather than 4 (the three-byte pattern 0x000001).  However, additional
zero-valued bytes may be present.
Exact conditions under which the minimum length is 4 rather than 3 bytes are
as follows (quoting):
When any of the following conditions are fulfilled, the zero_byte syntax
element shall be present.
-          the nal_unit_type within the nal_unit( ) is equal to 7 (sequence
parameter set) or 8 (picture parameter set)
-          the byte stream NAL unit syntax structure contains the first NAL
unit of an access unit in decoding order, as specified by subclause
7.4.1.2.3.
Best Regards,
Gary Sullivan
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From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Muneeb Dawood
Sent: Monday, February 11, 2024 2:07 PM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] Annex b format
Hi
I have analyzed the h.264 bitstream and the bitstream starts with byte
values of 0 0 0 and 1.
also these bit patterns are before the start of each nal unit. however in
the standard it says that the start code prefix are 3 bytes of values 0 0
and 1 in the annex b format. Could anyone explain the reason for this
incompatibility.. Thanks
Best Regards
Muneeb
Muneeb
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