我正在尝试从IP摄像机的RTSP MJPEG流构建JPEG图像。我使用CURL获取RTSP数据，然后遵循RTP Payload Format for JPEG-compressed video RFC。
我已经成功地能够形成不带量化表的JPEG图像。但是，对于类型为128的Q，我的算法无法正确组装JPEG图像。
我知道有像ffmpeg和gstreamer这样的库可以执行此解码，但由于其他问题，我无法使用它们。我还查看了其他帖子，并且认为我正在正确解码流。但是，在JPEG解压缩之后，图像看起来像这样。背景图像似乎正确，但图片上散布着不正确的水平条纹。
我已经成功地能够形成不带量化表的JPEG图像。但是，对于类型为128的Q，我的算法无法正确组装JPEG图像。
我知道有像ffmpeg和gstreamer这样的库可以执行此解码，但由于其他问题，我无法使用它们。我还查看了其他帖子，并且认为我正在正确解码流。但是，在JPEG解压缩之后，图像看起来像这样。背景图像似乎正确，但图片上散布着不正确的水平条纹。
这是我正在使用的代码片段：
while(!firstPacketFound) {
std::cout << "-----------RTP Packet: " << index++ << " starting at " << startOfRTPPacketIterator << "---------"<< endl;
isFirstPacket = false; isLastPacket = false;
// 0 - LibCurl header
// 1 - channel identifier
// 2, 3 - packet length
uint16_T packet_length_msb = f[ startOfRTPPacketIterator+2];
uint16_T packet_length_lsb = f[ startOfRTPPacketIterator+3];
packet_length = packet_length_msb << 8 | packet_length_lsb;
std::cout << "Packet Size: " << packet_length << endl;
// 4 - RTP Header - version + pasdding - generally 80
// 5 - Marker Bit + Payload 26 for JPEG
uint8_T rtp1 = f[ startOfRTPPacketIterator+4];
uint8_T payloadandmarkerbit = f[startOfRTPPacketIterator+5];
uint8_T markerbit =(payloadandmarkerbit >> 7) ;
uint8_T payload = payloadandmarkerbit & 0x7F;
std::cout << "Marker byte : " << int(payloadandmarkerbit) << endl;
if( payload != 26) {
cout << "NOT JPEG packet" << endl;
}
// 6 & 7 - sequence
// 8, 9, 10,11 - timestamp
//12, 13, 14, 15 - ssrc
uint16_t sequenceNumber_m = f[ startOfRTPPacketIterator+6];
uint16_t sequenceNumber_l = f[ startOfRTPPacketIterator+7];
uint16_t sequenceNumber = (sequenceNumber_m << 8) | sequenceNumber_l;
std::cout << "Sequence Number : " << sequenceNumber <<endl;
uint32_t timestamp1 = f[ startOfRTPPacketIterator+8];
uint32_t timestamp2 = f[ startOfRTPPacketIterator+9];
uint32_t timestamp3 = f[ startOfRTPPacketIterator+10];
uint32_t timestamp4 = f[ startOfRTPPacketIterator+11];
uint32_t timestamp = (timestamp1 <<24) | (timestamp2 <<16) | (timestamp3<<8) | timestamp4;
std::cout << "Timestamp : " << timestamp <<endl;
//--------------------JPEG Header ----------------------/
// 16 - type specific
// 17, 18, 19, - framgemnt offset
// 20 - type
// 21 - Q
// 22 - Width
//23- Height
uint32_t framgent_offset_1 = f[startOfRTPPacketIterator+17];
uint32_t framgent_offset_2 = f[startOfRTPPacketIterator+18];
uint32_t framgent_offset_3 = f[startOfRTPPacketIterator+19];
uint32_t framgent_offset = ((framgent_offset_1 << 16) | (framgent_offset_2 << 8) | (framgent_offset_3));
if (framgent_offset == 0)
{
isFirstPacket = true;
}
cout << "Fragment Offset: " << framgent_offset <<endl;
uint8_t type_specific = f[ startOfRTPPacketIterator+16];
cout << "type_specific: " << int(type_specific) <<endl;
uint8_t type = f[startOfRTPPacketIterator+20];
cout << "type : " << int(type) <<endl;
uint8_t Q = f[ startOfRTPPacketIterator+21];
cout << "Q: " << int(Q) <<endl;
uint8_t width = f[ startOfRTPPacketIterator+22];
cout << "width : " << int(width*8) <<endl;
uint8_t height = f[ startOfRTPPacketIterator+23];
cout << "height : " << int(height*8) <<endl;
// Check for restart markers
if ( type > 63) {
// For 64-127, restart markers are present in the JPEG data
//------------------Restart Marker Header------------------/
// 24, 25 - restart interval
// 26, 27 - F+L+ Restart Count
uint16_T restart_interval_m = uint16_T(f[startOfRTPPacketIterator+24]);
uint16_T restart_interval_l = uint16_T(f[startOfRTPPacketIterator+25]);
restart_interval = (restart_interval_m <<8 ) | restart_interval_l;
uint16_T restart_count_m = uint16_T(f[startOfRTPPacketIterator+26]);
uint16_T restart_count_l = uint16_T(f[startOfRTPPacketIterator+27]);
uint16_T restart_count = ((restart_count_m <<8 ) | restart_count_l) & 0x3F;
uint8_T F = restart_count_m >> 7;
uint8_T L = (restart_count_m & 0x40) >> 6;
cout << "restart_interval : " << restart_interval <<endl;
cout << "restart_count : " << restart_count <<endl;
cout << "F : " << int(F) <<endl;
cout << "L : " << int(L) <<endl;
}
//Check for quantization table in the first packet of the frame
if ( Q > 127) {
//--------------Quantization Header -----------------------/
// 28 - MBZ
// 29- Precision
// 30, 31 - length
// ...Quantization data
uint8_t MBZ = f[startOfRTPPacketIterator+28];
uint8_t precision = f[startOfRTPPacketIterator+29];
uint16_T qauntization_data_length = uint16_T(f[startOfRTPPacketIterator+30]) << 8 | uint16_T(f[startOfRTPPacketIterator+31]) ;
cout << "MBZ : " << int(MBZ) << endl;
cout << "precision : " << int(precision) << endl;
cout << "qauntization_data_length : " << qauntization_data_length << endl;
}
int indexOfPayload;
indexOfPayload = 28 ;
if (isFirstPacket) {
cout << "First packet found" << endl;
memcpy(lqt,&f[startOfRTPPacketIterator+32],64);
memcpy(cqt,&f[startOfRTPPacketIterator+32+65],64);
// MakeTables(Q,lqt,cqt);
unsigned char * p = new unsigned char[3000];
int sizeOfHeaders = MakeHeaders(p,type,width, height, lqt, cqt, restart_interval);
cout << "Size of headers:"<< sizeOfHeaders <<endl;
jpegPayload.insert(jpegPayload.end(),p,p+sizeOfHeaders+1);
delete p;
indexOfPayload = 32 +128 ;
}
int laststartOfRTPPacketIterator = startOfRTPPacketIterator;
// Look for start of frame marker
std::vector<uint8_t>::iterator startOfRTPPacketIterator2;
// startOfRTPPacketIterator2 = std::find(f.begin() + startOfRTPPacketIterator +packet_length ,f.end(),0x24);
startOfRTPPacketIterator2 = std::search(f.begin() + startOfRTPPacketIterator +packet_length,f.end(),startOfStreamMarker.begin(),startOfStreamMarker.begin()+2);
startOfRTPPacketIterator = (int)std::distance(f.begin(),startOfRTPPacketIterator2);
cout << "Adding payload data" << endl;
cout << "Starting at " << (laststartOfRTPPacketIterator+indexOfPayload) << endl;
cout << "Ending at " << startOfRTPPacketIterator << endl;
cout << "Size of vector before : " <<jpegPayload.size() <<endl;
// jpegPayload.reserve(framgent_offset);
jpegPayload.insert(jpegPayload.end(), &f[laststartOfRTPPacketIterator+indexOfPayload], &f[startOfRTPPacketIterator]);
cout << "Size of vector after : " <<jpegPayload.size() <<endl;
if (markerbit) {
firstPacketFound = true;
cout << "Last packet found" << endl;
isLastPacket = true;
FILE * image = fopen("image.jpeg","wb");
fwrite(&jpegPayload[0],sizeof(char), jpegPayload.size(), image);
fclose(image);
}
有什么想法可能出了问题吗？
- 我只从第一个RTP数据包中复制量化表。这是我从RFC中解释的。这正确吗？
- 我应该使用片段偏移字段来构建我的图像，还是只需将有效载荷数据附加到下一个数据包。
- 数据包超出了Libcurl数据包的长度。这是预期的吗。
谢谢！
更新：我还注意到工作的应用程序使用UDP流，而我将传输设置为TCP - const char *transport = "RTP/AVP/TCP;unicast;interleaved=0-1";
这会导致任何差异吗？一些摄像头只支持UDP而不支持TCP。