Hello, I'm a C.S. graduate student working on developing an optical tracking system as part of my research. I'm trying to figure out the best way to get a working, low-latency feed from an Ethernet camera. Unfortunately, when connecting to the camera with UDP, the image is badly corrupted. It gives errors such as the following:
Input #0, rtsp, from 'rtsp:// username:[email protected]/axis-media/media.amp': Metadata: title : Media Presentation Duration: N/A, start: 0.099878, bitrate: N/A Stream #0.0: Video: h264 (Baseline), yuvj420p, 640x480 [PAR 1:1 DAR 4:3], 90k tbr, 90k tbn, 180k tbc [avsink @ 0x7f9624001020] auto-inserting filter 'auto-inserted scaler 0' between the filter 'src' and the filter 'out' [scale @ 0x7f9624001700] w:640 h:480 fmt:yuvj420p -> w:640 h:480 fmt:yuv420p flags:0x4 [h264 @ 0x7f962c0073a0] corrupted macroblock 15 27 (total_coeff=-1)/0 [h264 @ 0x7f962c0073a0] error while decoding MB 15 27 [h264 @ 0x7f962c0073a0] concealing 154 DC, 154 AC, 154 MV errors [h264 @ 0x7f962c0b7760] negative number of zero coeffs at 29 12 [h264 @ 0x7f962c0b7760] error while decoding MB 29 12 [h264 @ 0x7f962c0b7760] concealing 740 DC, 740 AC, 740 MV errors 5.05 A-V: 0.000 s:0.0 aq= 0KB vq= 0KB sq= 0B f=0/0 Lots of Google searching has revealed that this is a fairly widespread problem common to both ffmpeg and avlib. We've tried multiple versions of both libraries, but the problem persists. It appears to be some kind of bug in the UDP protocol. If I specify the connection to use TCP instead; e.g., avplay 'rtsp://username:[email protected]/axis-media/media.amp?tcp' then it works, but the latency is very high (~1 sec) which is not good enough for an optical tracking system. Either fixing UDP or significantly improving the latency of the TCP connection would be an acceptable solution to the issue. Our research group probably has the knowledge needed to modify the code ourselves, but this would be significantly easier if we had some guidance beforehand, rather than just diving right in. Would anyone be able to advise me in this issue? Thank you for your time. -- James Walker Ph.D Student Dept. of Computer Science Michigan Technological University
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