For VOIP communication based on the SIP protocol, this field is usually located in the video negotiation sdp message, such as:
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- video 23456 RTP/AVP 121
- rtpmap:121 H264/90000
- fmtp: 121 profile-level-id=42801E; packetization-mode=1
42801E is divided into three parts
0x42 66
0x80 1000 0000 (binary)
0x1E 30
Corresponding to profile_idc (8 bits), profile_iop (8 bits), level_idc (8 bits), the meaning is as follows:
profile_idc: (hexadecimal)
66 Baseline profile (this is commonly used in VOIP)
77 Main profile
88 Extended profile
profile_iop: (8 bits respectively meaning)
constraint_set0_flag 1 represents that the encoded video sequence fully complies with all the clauses of A.2.1, and 0 is not necessarily.
constraint_set1 _flag1 represents that the encoded video sequence fully complies with all the clauses of A.2.2, and 0 is not necessarily.
constraint_set2_flag 1 represents that the encoded video sequence fully complies with all the provisions of A.2.3, and 0 is not necessarily.
Note: When any one of the above 3 bits is set to 1, it means that the video sequence fully complies with all the terms of A.2. When proifle_idc is 44, 100, 110, 122 or 244, these three bits must be 0.
constraint_set3_flag (1) When profile_idc is 66, 77 or 88 and level_idc is 11, 1 represents compliance with Annex A for level 1b, and 0 represents compliance with Annex for level 1.1.
(2) When profile_idc is 100 or 110, 1 represents compliance with Annex A for the High 10 Intra profile, and 0 is not necessarily.
(3) When profile_idc is 122, 1 represents compliance with Annex A for the High 4:2:2 Intra profile, and 0 is not necessarily.
(4) When profile_idc is 44, it is wrong that this data bit should be set to 1,0.
(5) When profile_idc is 244, 1 represents compliance with Annex A for the High 4:4:4 Intra profile, and 0 is not necessarily.
(6) When profile_idc is 66, 77 or 88 and level_idc is not 11, 1 is reserved for future use and should be set to 0, and the decoder should ignore the value of this data bit.
constraint_set4_flag (1) When profile_idc is 77, 88 or 100, 1 means that frame_mbs_only_flag is equal to 1, and 0 means that frame_mbs_only_flag may be 1 or 0.
(2) When profile_idc is 118 or 128, 1 represents that the coded video sequence complies with all the provisions of H.10.1.1, and 0 is not necessarily.
(3) When profile_idc is not the above two, 1 is reserved for future use and should be set to 0, and the decoder should ignore the value of this data bit.
constraint_set5_flag (1) When profile_idc is 77, 88 or 100, 1 means that the Bslice type does not exist in the coded video sequence, and 0 is not necessarily.
(2) When profile_idc is 118, 1 represents compliance with all the terms of H.10.1.2, and 0 is not necessarily.
(3) When profile_idc is not the above two, 1 is reserved for future use and should be set to 0, and the decoder should ignore the value of this data bit.
constraint_set6_flag is reserved and set to 0.
constraint_set7_flag is reserved and set to 0.
levle_idc ：
Level Maximum bit rate (BP, MP, EP) kbit/s high resolution example @maximum frame rate (maximum storage frame)
1 64 128*[email protected](8) 176*[email protected](4)
1b 128 128*[email protected] (8) 176*[email protected] (4)
1.1 192 176*[email protected](9) 320*[email protected](3) 352*[email protected](2)
1.2 384 320*[email protected](7) 352*[email protected](6)
1.3 768 320*[email protected](7) 352*[email protected](6)
2 2000 320*[email protected](7) 352*[email protected](6)
2.1 4000 352*[email protected](7) 352*[email protected](6)
2.2 4000 352*[email protected](12) 352*[email protected](10) 720*[email protected](6) 720*[email protected](5)
3 10000 352*[email protected](12) 352*[email protected](10) 720*[email protected](6) 720*[email protected](5)
3.1 14000 720*[email protected](13) 720*[email protected](11) 1280*[email protected](5)
3.2 20000 1280*[email protected](5) 1280*[email protected](4)
4 20000 1280*[email protected](9) 1920*[email protected](4) 2048*[email protected](4)
4.1 50000 1280*[email protected](9) 1920*[email protected](4) 2048*[email protected](4)
4.2 50000 1280*[email protected](9) 1920*[email protected](4) 2048*[email protected](4)
5 135000 1920*[email protected](13) 2048*[email protected](13) 2048*[email protected](12) 2560*[email protected](5) 3672*[email protected](5)
5.1 240000 1920*[email protected](16) 2560*[email protected](9) 3840*[email protected](5) 4096*[email protected](5) 4096*[email protected](5) 4096*[email protected](5)
5.2 240000 1920*[email protected](16) 2560*[email protected](9) 3840*[email protected](5) 4096*[email protected](5) 4096*[email protected](5) 4096*[email protected](5)
The value in the negotiation=level_idc*10 hexadecimal number, such as 1E=30 above, which means level 3. In addition, packetization-mode represents the payload type, and the range is 0-2 (0: NAL 1: non-interlaced 2: interlaced , Interlaced scan).