From:?http://blog.csdn.net/zblue78/article/details/5948538

H264的RTP中有三種不同的基本負載（Single NAL,Non-interleaved,Interleaved)

應用程序可以使用第一個字節來識別。

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在SDP中也說明了本次會話的屬性

SDP 參數?
下面描述了如何在 SDP 中表示一個 H.264 流:
. "m=" 行中的媒體名必須是 "video"
. "a=rtpmap" 行中的編碼名稱必須是 "H264".
. "a=rtpmap" 行中的時鐘頻率必須是 90000.
. 其他參數都包括在 "a=fmtp" 行中.
如:
m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; packetization-mode=1; sprop-parameter-sets=Z0IACpZTBYmI,aMljiA==

下面介紹一些常用的參數.
3.1 packetization-mode:?
表示支持的封包模式.?
當 packetization-mode 的值為 0 時或不存在時, 必須使用單一 NALU 單元模式.
當 packetization-mode 的值為 1 時必須使用非交錯(non-interleaved)封包模式.

當 packetization-mode 的值為 2 時必須使用交錯(interleaved)封包模式.

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每個打包方式允許的NAL單元類型總結(yes = 允許, no = 不允許, ig = 忽略)
????? Type?? Packet??? Single NAL??? Non-Interleaved??? Interleaved
?????????????????????? Unit Mode?????????? Mode???????????? Mode
????? -------------------------------------------------------------

????? 0????? undefined???? ig?????????????? ig?????????????? ig
????? 1-23?? NAL unit???? yes????????????? yes?????????????? no
????? 24???? STAP-A??????? no????????????? yes?????????????? no
????? 25???? STAP-B??????? no?????????????? no????????????? yes
????? 26???? MTAP16??????? no?????????????? no????????????? yes
????? 27???? MTAP24??????? no?????????????? no????????????? yes
????? 28???? FU-A????????? no????????????? yes????????????? yes
????? 29???? FU-B????????? no?????????????? no????????????? yes
????? 30-31? undefined???? ig?????????????? ig?????????????? ig

這個參數不可以取其他的值.

3.2 sprop-parameter-sets:?SPS,PPS
這個參數可以用于傳輸 H.264 的序列參數集和圖像參數 NAL 單元. 這個參數的值采用 Base64 進行編碼. 不同的參數集間用","號隔開.

3.3 profile-level-id:
這個參數用于指示 H.264 流的 profile 類型和級別. 由 Base16(十六進制) 表示的 3 個字節. 第一個字節表示 H.264 的 Profile 類型, 第三個字節表示 H.264 的 Profile 級別:

3.4 max-mbps:?
這個參數的值是一個整型, 指出了每一秒最大的宏塊處理速度.

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Rtp payload的第一個字節和264的NALU類似

?

+---------------+
|0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+
|F|NRI| Type? ? |
+---------------+

?

F: 1 個比特.

forbidden_zero_bit. 在 H.264 規范中規定了這一位必須為 0.

NRI: 2 個比特.

nal_ref_idc. 取 00 ~ 11, 似乎指示這個 NALU 的重要性, 如 00 的 NALU 解碼器可以丟棄它而不影響圖像的回放. 不過一般情況下不太關心這個屬性.

Type: 5 個比特.

nal_unit_type. 這個 NALU 單元的類型. 簡述如下:
0???? 沒有定義
1-23 NAL單元 單個 NAL 單元包.
24??? STAP-A?? 單一時間的組合包
24??? STAP-B?? 單一時間的組合包
26??? MTAP16?? 多個時間的組合包
27??? MTAP24?? 多個時間的組合包
28??? FU-A???? 分片的單元
29??? FU-B???? 分片的單元
30-31 沒有定義

例子：

0x5C=01011100 (F:0? NRI:10? Type:28) FU-A

0x41=01000001 (F:0? NRI:10? Type:01)Single NAL

0x68=01000100 (F:0? NRI:10? Type:08)Single NAL

?

Single NAL Unit Mode?:Type[1-23]?packetization-mode=0

對于 NALU 的長度小于 MTU 大小的包, 一般采用單一 NAL 單元模式.
對于一個原始的 H.264 NALU 單元常由?[Start Code] [NALU Header] [NALU Payload]?三部分組成, 其中 Start Code 用于標示這是一個 NALU 單元的開始, 必須是 "00 00 00 01" 或 "00 00 01", NALU 頭僅一個字節, 其后都是 NALU 單元內容.
打包時去除 "00 00 01" 或 "00 00 00 01" 的開始碼, 把其他數據封包的 RTP 包即可.

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Non-interleaved Mode:Type[1-23,24,28]?packetization-mode=1

?????? Type=[1-23]的情況 參照?packetization-mode=0

Type=28 FU-A

+---------------+---------------+
|0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|NRI| Type:28 |S|E|R| Type? ? |
+---------------+---------------+

?

S:開始標志

E:結束標志 (與 Mark相同）

R:必須為0

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Type:h264的NALU Type

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例：

?

0x7C85=01111100 10000101 (開始包)

0x7C05=01111100 00000101 (中間包)

0x7C45=01111100 01000101 (結束包)

Type=23? STAP-A

0???????????? ? 1???????????? 2???????????????? 3
|0 1 2 3 4 5 6 7|8 9 0 1 2 3 4|5 6 7 8 9 0 1 2 3|4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|????????????????????????? RTP Header?????????????????????????? |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|STAP-A NAL HDR |???????? NALU 1 Size?????????? | NALU 1 HDR??? |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|???????????????????????? NALU 1 Data?????????????????????????? |
:?????????????????????????????????????????????????????????????? :
+?????????????? +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

|?????????????? | NALU 2 Size?????????????????? | NALU 2 HDR??? |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|???????????????????????? NALU 2 Data?????????????????????????? |
:?????????????????????????????????????????????????????????????? :
|?????????????????????????????? +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|?????????????????????????????? :...OPTIONAL RTP padding??????? |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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[cpp]?view plaincopy

class?H264NALUParser????

{??

public:??

????H264NALUParser(int?width?,?int?height);??

????H264NALUParser();??

????virtual?~H264NALUParser();??

????void?SetBuffer(unsigned?char?*?buffer,int?len,int?f,int?nri,int?type);??

????BOOL?readOnePacket(unsigned?char?*?buffer,int?&len);??

????BOOL?isPacketOutstanding();??

private:??

????unsigned?char?*?m_pNaluBuffer;??//?NALU數據指向的緩沖區的指針??

????unsigned?int?m_nNaluSize;???????//?NALU數據緩沖區的大小??

????unsigned?char?*?m_pCurNaluPos;??//指向下一個數據包要讀取的緩沖區指針??

????int?m_nFrameWidth;??

????int?m_nFrameHeight;??

????int?m_nPacketCounts;??

????int?m_nPacketSeqNum;??

????int?m_nF;??

????int?m_nNRI;??

????int?m_nType;??

????enum?{??

????????STAP_A?=?24,??

????????STAP_B?=?25,??

????????MTAP16?=?26,??

????????MTAP24?=?27,??

????????FU_A???=?28,??

????????FU_B???=?29??

????};??

};????

??

//?class?H264NALUParser?/??

H264NALUParser::H264NALUParser(int?width?,?int?height)??

{??

????m_nFrameWidth???=?width;??

????m_nFrameHeight??=?height;??

????m_pNaluBuffer???=?NULL;??

????m_nNaluSize?????=?0;??

????m_nPacketCounts?=?0;??

????m_nPacketSeqNum?=?0;??

????m_nF????????????=?0;??

????m_nNRI??????????=?0;??

????m_nType?????????=?0;??

}??

H264NALUParser::H264NALUParser()??

{??

????m_pNaluBuffer???=?NULL;??

????m_nNaluSize?????=?0;??

????m_nPacketCounts?=?0;??

????m_nPacketSeqNum?=?0;??

????m_nF????????????=?0;??

????m_nNRI??????????=?0;??

????m_nType?????????=?0;??

}??

H264NALUParser::~H264NALUParser()??

{??

}??

void?H264NALUParser::SetBuffer(unsigned?char?*?buffer,int?len,int?f,int?nri,int?type)??

{??

????m_pNaluBuffer???=?buffer;??

????m_nNaluSize?????=?len;??

????m_nF????????????=?f;??

????m_nNRI??????????=?nri;??

????m_nType?????????=?type;??

????m_pCurNaluPos???=?m_pNaluBuffer;??

????m_nPacketCounts?=?(m_nNaluSize?+?H264_MTU?-?1)?/?H264_MTU;??

????m_nPacketSeqNum?=?0;??

}??

BOOL?H264NALUParser::readOnePacket(unsigned?char?*?buffer,int?&len)??

{??

????if(m_pCurNaluPos?>=?m_pNaluBuffer?+?m_nNaluSize)??

????{??

????????return?FALSE;??

????}??

????struct?h264_rtp_hdr?header;??

????int?headersize;??

????unsigned?char?*?pCurBuf?=?buffer;??

????if(m_nNaluSize?<=?H264_MTU)//?Single?NALU??

????{??

????????header.SingleNALU.f?????=?m_nF;??

????????header.SingleNALU.nri???=?m_nNRI;??

????????header.SingleNALU.type??=?m_nType;??

????????headersize?=?sizeof(header.SingleNALU);??

????????memcpy(pCurBuf,&(header.SingleNALU),headersize);??

????????pCurBuf?+=?headersize;??

????}??

????else//?FU-A??

????{??

????????header.FU_A.f???????????=?m_nF;??

????????header.FU_A.nri?????????=?m_nNRI;??

????????header.FU_A.type_indicator??=?FU_A;??

????????if(0?==?m_nPacketSeqNum)??

????????{??

????????????header.FU_A.s???????=?1;??

????????}??

????????else??

????????{??

????????????header.FU_A.s???????=?0;??

????????}??

????????if(m_nPacketSeqNum?==?m_nPacketCounts?-?1)??

????????{??

????????????header.FU_A.e???????=?1;??

????????}??

????????else??

????????{??

????????????header.FU_A.e???????=?0;??

????????}??

????????header.FU_A.r???????????=?0;??

????????header.FU_A.type_header?=?m_nType;??

????????//??

????????headersize?=?sizeof(header.FU_A);??

????????memcpy(pCurBuf,&(header.FU_A),headersize);??

????????pCurBuf?+=?headersize;??

????}??

????if(m_nPacketSeqNum?<?m_nPacketCounts?-?1)??

????{??

????????memcpy(pCurBuf,m_pCurNaluPos,H264_MTU);??

????????m_pCurNaluPos?+=?H264_MTU;??

????????len?=?headersize?+?H264_MTU;??

????}??

????else??

????{??

????????int?remainLen?=?m_nNaluSize?%?H264_MTU;??

????????if(0?==?remainLen)??

????????{??

????????????remainLen?=?H264_MTU;??

????????}??

????????memcpy(pCurBuf,m_pCurNaluPos,remainLen);??

????????m_pCurNaluPos?+=?remainLen;??

????????len?=?headersize?+?remainLen;??

????}??

????m_nPacketSeqNum?++;??

????return?TRUE;??

}??

BOOL?H264NALUParser::isPacketOutstanding()??

{??

????return?(m_nPacketSeqNum?<?m_nPacketCounts);??

}??

Interleaved Mode:Type[26-29]?packetization-mode=2

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待續

?

STAP-B

MTAP16

MTAP24

FU-B

總結

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