[libav-api] Problems with RTSP Feed from Ethernet Webcam

James Walker jwwalker at mtu.edu
Fri Jul 27 20:34:12 CEST 2012


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:password at 192.168.0.90/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:password@192.168.0.90/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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