Video Compression H.264, ITU-T, MPEG-4
Breif Description of nal_ref_idc Value in H.246 NALU
Author: Yumi Chan 2017-01-19 14 Comments
late update because of my study!
A quite update of myself: I have actually stopped working on H.264 and MP4 for some time but will probably pick up again in the
As in the article Introduction to H.264: (1) NAL Unit, Suji Mani asked what is the exact meaning of different values in nal_ref_idc. In
fact, nal_ref_idc is base on “Start Code Value” and represents the priority of the current frame (i.e. how important of the frame –
the higher the value, the more important the frame). Here is a list of nal_ref_idc values with the corresponding Start Code Type:
Start Code Type nal_ref_idc values (in binary) nal_ref_idc values (in decimal)
Sequence header 11 3
Picture header of I-frame 11 3
Slice data of I-frame 11 3
Picture header of P-frame 10 2
Slice data of P-frame 10 2
Picture header of B-frame 01 1
Slice data of B-frame 01 1
Video extension start code 00 0
User data start code 00 0
Video edit start code 00 0
Let me clarify a bit. nal_ref_idc is actually telling you what is the type of the current frame, which implies that what information you
could get in this frame.
The example in Introduction to H.264: (1) NAL Unit is the beginning of a H.246 raw data. Let’s check the example again.