H264 Network Abstraction Layer Packet (NALU)
Posted: Mon May 19, 2014 12:06 am
All NALUs consist of a single NALU Type octet, which also serves as
the payload header. The payload of a NALU follows immediately.
The NALU type octet has the following format:
+---------------+
|0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+
|F|NSI| Type |
+---------------+
F: 1 bit
The Forbidden bit, when zero, indicates a bit error free NAL
unit. The JVT specification declares a value of 1 as a syntax
violation. Hence, when set, the decoder is advised that bit
errors may be present in the payload or in the NALU type octet.
A prudent reaction of decoders that are incapable of handling
bit errors is to discard such packets.
NSI: 2 bits
NAL Storage IDC. A value of 00 indicates that the content of
the NALU is not used to reconstruct stored pictures (that can be
Wenger et. al. Expires December 2002 [Page 5]
Internet Draft 21 September 2002
used for future reference). Such NALUs can be discarded without
risking the integrity of the reference pictures. Values above
00 indicate that the decoding of the NALU is required to
maintain the integrity of the reference pictures. Furthermore,
values above 00 indicate the relative transport priority, as
determined by the encoder. Intelligent network elements can use
this information t protect more important NALUs better than less
important NALUs. 11 is the highest transport priority, followed
by 10, then by 01 and, finally, 00 is the lowest.
Type: 5 bits
The NAL Unit payload type as defined in table 7.1 of [2].
For a reference of all currently defined NALU types and their
semantics please refer to section 7.1 in [2].
the payload header. The payload of a NALU follows immediately.
The NALU type octet has the following format:
+---------------+
|0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+
|F|NSI| Type |
+---------------+
F: 1 bit
The Forbidden bit, when zero, indicates a bit error free NAL
unit. The JVT specification declares a value of 1 as a syntax
violation. Hence, when set, the decoder is advised that bit
errors may be present in the payload or in the NALU type octet.
A prudent reaction of decoders that are incapable of handling
bit errors is to discard such packets.
NSI: 2 bits
NAL Storage IDC. A value of 00 indicates that the content of
the NALU is not used to reconstruct stored pictures (that can be
Wenger et. al. Expires December 2002 [Page 5]
Internet Draft 21 September 2002
used for future reference). Such NALUs can be discarded without
risking the integrity of the reference pictures. Values above
00 indicate that the decoding of the NALU is required to
maintain the integrity of the reference pictures. Furthermore,
values above 00 indicate the relative transport priority, as
determined by the encoder. Intelligent network elements can use
this information t protect more important NALUs better than less
important NALUs. 11 is the highest transport priority, followed
by 10, then by 01 and, finally, 00 is the lowest.
Type: 5 bits
The NAL Unit payload type as defined in table 7.1 of [2].
For a reference of all currently defined NALU types and their
semantics please refer to section 7.1 in [2].