level用来表明一个profile的解码器的性能要求的范围，例如最大图片分配了，帧频，比特率等等。对于解码器，一个指定的level要求可以对该level以及低于该level的码流进行解码。（A decoder that conforms to agiven level is required to be capable of decoding all bitstreams that areencoded for that level and for all lower levels. 来源：）
Levels with maximum property values
Level
Max macroblocks
Max video bit rate (VCL)
Examples for high resolution @
frame rate
(max stored frames)
per second
per frame
BP, XP, MP
(kbit/s)
HiP
(kbit/s)
Hi10P
(kbit/s)
Hi422P, Hi444PP
(kbit/s)
1
1,485
99
64
80
192
256
128×96@30.9 (8)
176×144@15.0 (4)
1b
1,485
99
128
160
384
512
128×96@30.9 (8)
176×144@15.0 (4)
1.1
3,000
396
192
240
576
768
176×144@30.3 (9)
320×240@10.0 (3)
352×288@7.5 (2)
1.2
6,000
396
384
480
1,152
1,536
320×240@20.0 (7)
352×288@15.2 (6)
1.3
11,880
396
768
960
2,304
3,072
320×240@36.0 (7)
352×288@30.0 (6)
2
11,880
396
2,000
2,500
6,000
8,000
320×240@36.0 (7)
352×288@30.0 (6)
2.1
19,800
792
4,000
5,000
12,000
16,000
352×480@30.0 (7)
352×576@25.0 (6)
2.2
20,250
1,620
4,000
5,000
12,000
16,000
352×480@30.7(10)
352×576@25.6 (7)
720×480@15.0 (6)
720×576@12.5 (5)
3
40,500
1,620
10,000
12,500
30,000
40,000
352×480@61.4 (12)
352×576@51.1 (10)
720×480@30.0 (6)
720×576@25.0 (5)
3.1
108,000
3,600
14,000
17,500
42,000
56,000
720×480@80.0 (13)
720×576@66.7 (11)
1280×720@30.0 (5)
3.2
216,000
5,120
20,000
25,000
60,000
80,000
1,280×720@60.0 (5)
1,280×1,024@42.2 (4)
4
245,760
8,192
20,000
25,000
60,000
80,000
1,280×720@68.3 (9)
1,920×1,080@30.1 (4)
2,048×1,024@30.0 (4)
4.1
245,760
8,192
50,000
62,500
150,000
200,000
1,280×720@68.3 (9)
1,920×1,080@30.1 (4)
2,048×1,024@30.0 (4)
4.2
522,240
8,704
50,000
62,500
150,000
200,000
1,920×1,080@64.0 (4)
2,048×1,080@60.0 (4)
5
589,824
22,080
135,000
168,750
405,000
540,000
1,920×1,080@72.3 (13)
2,048×1,024@72.0 (13)
2,048×1,080@67.8 (12)
2,560×1,920@30.7 (5)
3,680×1,536@26.7 (5)
5.1
983,040
36,864
240,000
300,000
720,000
960,000
1,920×1,080@120.5 (16)
4,096×2,048@30.0 (5)
4,096×2,304@26.7 (5)
编解码学习笔记（五）：Mpeg系列——AAC音频
下面资料来自wiki。AAC在MPEG2和MPEG4中定义。