Identify h264 profile and level from profile-level-id in sdp?

Question

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?

Answer 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

Answer 2

Refer to following table from RFC 6184: Table 5. Combinations of profile_idc and profile-iop representing the same sub-profile corresponding to the full set of coding tools supported by one profile. In the following, x may be either 0 or 1, while the profile names are indicated as follows. CB: Constrained Baseline profile, B: Baseline profile, M: Main profile, E: Extended profile, H: High profile, H10: High 10 profile, H42: High 4:2:2 profile, H44: High 4:4:4 Predictive profile, H10I: High 10 Intra profile, H42I: High 4:2:2 Intra profile, H44I: High 4:4:4 Intra profile, and C44I: CAVLC 4:4:4 Intra profile.

      Profile     profile_idc        profile-iop
                  (hexadecimal)      (binary)

      CB          42 (B)             x1xx0000
         same as: 4D (M)             1xxx0000
         same as: 58 (E)             11xx0000
      B           42 (B)             x0xx0000
         same as: 58 (E)             10xx0000
      M           4D (M)             0x0x0000
      E           58                 00xx0000
      H           64                 00000000
      H10         6E                 00000000
      H42         7A                 00000000
      H44         F4                 00000000
      H10I        6E                 00010000
      H42I        7A                 00010000
      H44I        F4                 00010000
      C44I        2C                 00010000

It is Baseline Profile Level 2.0.