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LFG4 Latency issues



  • hello all,

    I have a LFG4 installed in my MacPro with 2.8Ghz quadCore Xeon, 20GB Ram and dual ATI Radeon HD5770 
    I am capturing two NTSC streams at half res from the live IMAG cameras, and compositing them with my video content picture in picture style. I am running at full 30fps but there is still a substantial amount of latency and "lip sync" issues with the audio which runs straight through FOH console. Are there any ways I could optimize my system or Isadora to reduce latency? It seems to me that others are running live video just fine, even at higher resolutions.
    Thanks,
    Josua

  • Tech Staff

    @josua
    There are many things that can cause the latency. You can try different things to see what causes most delay.
    Connect your camera directly to an old tv screen and compare the latency to the sound. Then connect the camera directly to the projector you are using how big is the delay compared to the tv screen? Now you know if your projector causes a bigger amount of delay. Then if you connect your camera to your computer and go fullscreen on your computers screen, how big is the delay there etc. etc.
    That way you get an idea where the delays come from and which device causes most.

    What version of Isadora are you using?

    Best
    Michel



  • If you want to send live camera direct to a projector use a video mixer, you can use a matrix as well so you can still have the input in Isadora, otherwise you will get a big delay. Most video mixers can do a PIP composite also.

    You can get delay at every point of your system, many non pro cameras have a delay before they even output the image, your capture card will have a delay and your compositing will add a delay and your projector will also add a delay.
    Without a ton of pro gear you will get a delay, big pro projectors also have a big delay. If you are in a big space you can delay the audio to match (if it is not too much- ie just compensating for a projector, not a whole chain of delays).
    I have dealt with this problem many times and a video mixer is the way (There are things you can do to minimise the delay if you have to go through a computer, but Isadora does not give you so many options, mostly getting the fastest possible hardware and then programming your video effects in something super fast like pure opengl or openCL).
    Check this thread for an explanation of how to measure your delay precisely.
    http://troikatronix.com/troikatronixforum/discussion/comment/5880#Comment_5880
    Fred

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