H.264 Profile、Level、Encoder三张简图 (fps = AVCodecContext->time_base.den / AVCodecContext->time_base.num)

H.264 Profiles

Profiles are sets of capabilities. If your black box only supports the Baseline profile it'll not be able to decode a stream using High capabilities.

In VLC you can set the H.264 profile to be used by the x264 encoder like this:

--sout="#transcode{vcodec=h264,venc=x264{profile=baseline}...

H.264 Levels

Think of levels as a constraint/indicator of required decoder performance. If a decoder supports a certain level for a certain profile then it must be able to decode streams at that level and any of the lower levels.

First of all, the level for 640x480 @ 30 fps is 3 and not 2.2.

You can calculate this as following:

macrobolocks = ceil(640/16) * ceil(480/16) = 1200
macroblocks/s = macroblocks * 30 = 36000

The reason for ceil is that non-mod16 resolution are padded to a multiple of 16.

You then take a look at the H.264 Levels. You are within the frame size limit for 2.2 which is 1620 but the max decoding speed is greater than 20252 so you have to choose the next level wich is 3. You'll also have to consider the maximum bitrate for the Baseline profile in that table.

If you have an Android device you can download my H.264 Calculator app from the Amazon App Store (I can send you the apk if you don't like their Orwellian app permissions)

The x264 encoder will automatically choose a level based on your encoding parameters. With VLC you can actually set the flag yourself using something like:

--sout="#transcode{vcodec=h264,venc=x264{profile=baseline,level=22}"...

Beware, this sets the encoder output flag and doesn't actually produce a Level 2.2 stream. You can put any values you want, so it's possible to mark a Full HD stream at 60 fps as Level 2.2 even if it's nowhere the level limits.

VLC Transcoding

If you want to make sure you're sending a correct stream you'll need to transcode the source material. This is an example for 640x480 @ 30 fps which results in a Level 3 H.264 stream like I showed you above. If you want Level 2.2 you'll need to lower the resolution or framerate or both. Your video bitrate can go lower too in that case.

cvlc input.mp4 --sout="#transcode{vcodec=h264,venc=x264{profile=baseline},fps=30,width=640,height=480,vb=1372,acodec=mpga,ab=128,channels=2,samplerate=44100}:rtp{...}

Mediainfo

Mediainfo is a great tool to get information about a media file. You can check the specs of your input files, but it won't help you detect a wrong level which was forced into or wrongfully chosen by the encoder. The safest way is to re-encode.

下面的这个表拷贝自：  https://en.wikipedia.org/wiki/H.264/MPEG-4_AVC#Levels

Levels

As the term is used in the standard, a "level" is a specified set of constraints that indicate a degree of required decoder performance for a profile. For example, a level of support within a profile specifies the maximum picture resolution, frame rate, and bit rate that a decoder may use. A decoder that conforms to a given level must be able to decode all bitstreams encoded for that level and all lower levels.

Levels with maximum property values

Level	Max decoding speed		Max frame size		Max video bit rate for video coding layer (VCL) kbit/s			Examples for high resolution @ highest frame rate (max stored frames) Toggle additional details
	Luma samples/s	Macroblocks/s	Luma samples	Macroblocks	Baseline, Extended and Main Profiles	High Profile	High 10 Profile
1	380,160	1,485	25,344	99	64	80	192	128×96@30.9 (8) 176×144@15.0 (4)
1b	380,160	1,485	25,344	99	128	160	384	128×96@30.9 (8) 176×144@15.0 (4)
1.1	768,000	3,000	101,376	396	192	240	576	176×144@30.3 (9) 320×240@10.0 (3) 352×288@7.5 (2)
1.2	1,536,000	6,000	101,376	396	384	480	1,152	320×240@20.0 (7) 352×288@15.2 (6)
1.3	3,041,280	11,880	101,376	396	768	960	2,304	320×240@36.0 (7) 352×288@30.0 (6)
2	3,041,280	11,880	101,376	396	2,000	2,500	6,000	320×240@36.0 (7) 352×288@30.0 (6)
2.1	5,068,800	19,800	202,752	792	4,000	5,000	12,000	352×480@30.0 (7) 352×576@25.0 (6)
2.2	5,184,000	20,250	414,720	1,620	4,000	5,000	12,000	352×480@30.7 (12) 352×576@25.6 (10) 720×480@15.0 (6) 720×576@12.5 (5)
3	10,368,000	40,500	414,720	1,620	10,000	12,500	30,000	352×480@61.4 (12) 352×576@51.1 (10) 720×480@30.0 (6) 720×576@25.0 (5)
3.1	27,648,000	108,000	921,600	3,600	14,000	17,500	42,000	720×480@80.0 (13) 720×576@66.7 (11) 1,280×720@30.0 (5)
3.2	55,296,000	216,000	1,310,720	5,120	20,000	25,000	60,000	1,280×720@60.0 (5) 1,280×1,024@42.2 (4)
4	62,914,560	245,760	2,097,152	8,192	20,000	25,000	60,000	1,280×720@68.3 (9) 1,920×1,080@30.1 (4) 2,048×1,024@30.0 (4)
4.1	62,914,560	245,760	2,097,152	8,192	50,000	62,500	150,000	1,280×720@68.3 (9) 1,920×1,080@30.1 (4) 2,048×1,024@30.0 (4)
4.2	133,693,440	522,240	2,228,224	8,704	50,000	62,500	150,000	1,280×720@145.1 (9) 1,920×1,080@64.0 (4) 2,048×1,080@60.0 (4)
5	150,994,944	589,824	5,652,480	22,080	135,000	168,750	405,000	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) 3,672×1,536@26.7 (5)
5.1	251,658,240	983,040	9,437,184	36,864	240,000	300,000	720,000	1,920×1,080@120.5 (16) 2,560×1,920@51.2 (9) 3,840×2,160@31.7 (5) 4,096×2,048@30.0 (5) 4,096×2,160@28.5 (5) 4,096×2,304@26.7 (5)
5.2	530,841,600	2,073,600	9,437,184	36,864	240,000	300,000	720,000	1,920×1,080@172.0 (16) 2,560×1,920@108.0 (9) 3,840×2,160@66.8 (5) 4,096×2,048@63.3 (5) 4,096×2,160@60.0 (5) 4,096×2,304@56.3 (5)

The maximum bit rate for High Profile is 1.25 times that of the
Base/Extended/Main Profiles, 3 times for Hi10P, and 4 times for
Hi422P/Hi444PP.

The number of luma samples is 16x16=256 times the number of
macroblocks (and the number of luma samples per second is 256 times the
number of macroblocks per second).

http://xcshen.blog.51cto.com/2835389/552669

H.264有四种画质级别,分别是BP、EP、MP、HP：

　　1、BP-Baseline Profile：基本画质。支持I/P 帧，只支持无交错（Progressive）和CAVLC；
　　2、EP-Extended profile：进阶画质。支持I/P/B/SP/SI 帧，只支持无交错（Progressive）和CAVLC；
　　3、MP-Main profile：主流画质。提供I/P/B 帧，支持无交错（Progressive）和交错（Interlaced），
　　　 也支持CAVLC 和CABAC 的支持；
　　4、HP-High profile：高级画质。在main Profile 的基础上增加了8x8内部预测、自定义量化、 无损视频编码和更多的YUV 格式；

想
要说明H.264 HP与H.264
MP的区别就要讲到H.264的技术发展了。JVT于2003年完成H.264基本部分标准制定工作，包含Baseline
profile、Extended profile和Main profile，分别包括不同的编码工具。之后JVT又完成了H.264
FRExt（即：Fidelity Range Extensions）扩展部分（Amendment）的制定工作，包括High
profile（HP）、High 10 profile（Hi10P）、High 4:2:2 profile（Hi422P）、High 4:4:4
profile（Hi444P）4个profile。

　
　H.264 Baseline profile、Extended profile和Main
profile都是针对8位样本数据、4:2:0格式的视频序列，FRExt将其扩展到8～12位样本数据，视频格式可以为4:2:0、4:2:2、
4:4:4，设立了High profile（HP）、High 10 profile（Hi10P）、High 4:2:2
profile（Hi422P）、High 4:4:4 profile（Hi444P） 4个profile，这4个profile都以Main
profile为基础。

在
相同配置情况下，High profile（HP）可以比Main profile（MP）节省10%的码流量，比MPEG-2
MP节省60%的码流量，具有更好的编码性能。根据应用领域的不同，Baseline profile多应用于实时通信领域，Main
profile多应用于流媒体领域，High profile则多应用于广电和存储领域。

H.264 Baseline Profile对应MPEG-4 SP
H.264 Main Profile对应MPEG-4 ASP
H.264 Extended Profile对应MPEG-4 ARTS or FGS
H.264 Baseline Profile对应MPEG-4 Studio。

H.264 Profile、Level、Encoder三张简图

【整理者】61ic.com
【提供者】QuestionMark         
【详细说明】H.264 Profile、Level、Encoder三张简图
取自
wikipedia

h.264 profile

h.264 level

 
h.264 software encoder

本文出自 “流媒体技术工程组” 博客，请务必保留此出处http://xcshen.blog.51cto.com/2835389/552669

对于640*480，可以参考如下的level：

Level	VBV maximum bit rate [1000bits/s]	VBV buffer size [1000bits]	Macroblocks/s	Resolution and frame rate
1	64	175	1485	128×96@30 or 176×144@15
1b	128	350	1485	128×96@30 or 176×144@15
1.1	192	500	3000	176×144@30 or 320×240@10
1.2	384	1000	6000	176×144@60 or 320×240@20
1.3	768	2000	11880	352×288@30
2	2000	2000	11880	352×288@30
2.1	4000	4000	19800	352×288@50
2.2	4000	4000	20250	352×288@50 or 640×480@15
3	10000	10000	40500	720×480@30 or 720×576@25
3.1	14000	14000	108000	1280×720@30
3.2	20000	20000	216000	1280×720@60
4	20000	25000	245760	1920×1088@30 or 2Kx1K@30
4.1	50000	62500	245760	1920×1088@30 or 2Kx1K@30
4.2	50000	62500	522240	1920×1088@60 or or 2Kx1K@60
5	135000	135000	589824	2560×1920@30
5.1	240000	240000	983040	4Kx2K@30 or 4096×2304@25

从实践来看，640*480@15，级别可设置为（级别必须是2.2）：

2.2

4000

4000

20250

352×288@50 or 640×480@15

Max macroblocks 可设置为 1620

从实践来看，640*480@30，级别可设置为（级别必须是3.0）：

3.0

10000

4000

36000

640×480@30

Max macroblocks 可设置为1620