rtsp/rtp 新增支持mjpeg编码 (#2166)

* Trying to send mjpeg via MultiMediaSourceMuxer

* Improved JPEGRtpEncoder::inputFrame code but still not working

* 优化代码

* 完善jpeg相关逻辑

* Micro fix

* FrameJPEG renamed to JPEGFrame according to ZLM style

* Modified  JPEGRtpEncoder::inputFrame and JPEGRtpEncoder::rtp_send_jpeg

* getVideoHeight(), getVideoWidth() and getVideoFps() in JPEGTrack

* mjpeg rtp打包避免内存拷贝/修复mjpeg rtp解包huffman_table size字段错误的bug

* 支持mjpeg pix type

* 优化性能

* add bom header

src/Extension/JPEG.cpp

@@ -0,0 +1,53 @@
+#include "JPEG.h"
+#include "Rtsp/Rtsp.h"
+#include "Util/util.h"
+
+using namespace toolkit;
+
+namespace mediakit {
+
+bool JPEGTrack::inputFrame(const Frame::Ptr &frame) {
+    if (!ready()) {
+        if ((_height & _width) > 0) {
+            if (_tmp == 0) _tmp = frame->dts();
+            else _fps = 1000.0 / (frame->dts() - _tmp);
+        } else getVideoResolution((uint8_t*)frame->data(), frame->size());
+        return false;
+    }
+    return VideoTrack::inputFrame(frame);
+}
+
+void JPEGTrack::getVideoResolution(const uint8_t *buf, int len) {
+    for (int i = 0; i < len - 8; i++) {
+        if (buf[i] != 0xff)
+            continue;
+        if (buf[i + 1] == 0xC0 /*SOF0*/) {
+            _height = buf[i + 5] * 256 + buf[i + 6];
+            _width = buf[i + 7] * 256 + buf[i + 8];
+            return;
+        }
+    }
+}
+
+class JPEGSdp : public Sdp {
+public:
+    JPEGSdp(int bitrate): Sdp(90000, Rtsp::PT_JPEG) {
+        _printer << "m=video 0 RTP/AVP " << (int)getPayloadType() << "\r\n";
+        if (bitrate) {
+            _printer << "b=AS:" << bitrate << "\r\n";
+        }
+        _printer << "a=control:trackID=" << (int)TrackVideo << "\r\n";
+    }
+
+    std::string getSdp() const { return _printer; }
+
+    CodecId getCodecId() const { return CodecJPEG; }
+
+private:
+    _StrPrinter _printer;
+};
+
+Sdp::Ptr JPEGTrack::getSdp() {
+    return std::make_shared<JPEGSdp>(getBitRate() / 1024);
+}
+} // namespace mediakit