Measure e2e latency for each frame

[jheo4]

When the frame travels between the server and client via RTP, it is not easy to capture the e2e latency of each frame. It is because UDP-based RTP may drop some packets and miss frames, and it can happen on both sides: the server and the client. To address this issue, I have to be able to track each frame. Since the current use case is synchronized with mxre pipeline, I don't need to consider different frequencies between mxre and the application.

• [x] modify mxre frame to have tracking info: index and timestamp stamped when the frame is generated.
• [x] made all codes handling mxre frame compatible with new attributes
• [x] check an opportunity to add side data to AVPacket via RTP and embed frame tracking info to AVPacket

The following issues are commented in this thread.

[jheo4]

The side data of avpacket is not sent as a part of rtp frame. There is a need for another channel for tracking.

• [x] add a channel for sending/receiving frame tracking along with rtp frame
• [x] test the streaming with tracking channel between the server and client
• [x] measure the round-trip time of each frame; there might be another issue with it.
• [x] Latency breakdown of each RTP kernels; kernel-level optimization for streaming

[jheo4]

After the latency breakdown, I found sws_scale(struct SwsContext *c, const uint8_t *const *srcSlice, const int *srcStride, int srcSliceY, int srcSliceH, uint8_t *const *dst, const int *dstStride) dominated the latency for streaming. sws_scale involves copying frame, converting pixel formats, and re-scaling. It must be addressed for practical RTP streaming.

• [x] check pixel conversions between encoders/decoders and mxre::Frame.
• [x] check direct usage of mxre::Frame for AVFrame
• [x] find alternatives for converting packet formats
• [x] check pixel format conversion with OpenCV
• [x] find matching formats between encoder/decoder pairs and cv algorithms
• [x] check the results
• [x] measure the latency for pixel format conversions

[jheo4]

Replaced swscaler with cvColor.