问题
In a SIP video call, the receiver of the video stream respond with the capabilities of its decoder.
The parameter which defines that is the profile-level-id. Here is an example value of the profile-level-id parameter: 428014
RFC 6184 defined that as
A base16 [7] (hexadecimal) representation of the following three bytes in the sequence parameter set NAL unit is specified in 1: 1) profile_idc, 2) a byte herein referred to as profile-iop, composed of the values of constraint_set0_flag, constraint_set1_flag, constraint_set2_flag, constraint_set3_flag, constraint_set4_flag, constraint_set5_flag, and reserved_zero_2bits in bit- significance order, starting from the most-significant bit, and 3) level_idc.
According to that, the following parameters from the example value can be identified:
- profile_idc 42
- profile-iop 82
- level-idc 14
How to relate those numbers to the profiles and levels defined for h264?
回答1:
For such things you should read actual H.264 spec not Wikipedia. Using it you can parse your example as
- profile_idc 0x42 == 66 so it is Baseline profile
- profile-iop 0x80 mean constraint_set0_flag=1 (so it is Constrained Baseline profile) and others 0
- level-idc 0x14 == 20 so it is Level 2.0
So result is Constrained Baseline profile Level 2.0
来源：https://stackoverflow.com/questions/22960928/identify-h264-profile-and-level-from-profile-level-id-in-sdp