Video latency



  • Hi there,

    This is a beginner's live feed question:
    I've got a pretty basic set-up using a Macbook Pro with 8GB RAM and 2.6 Intel Core Processor, a Canon HV30 with a 8m long firewire cable and a VGA output to a VGA splitter for a monitor and a projector. 
    Now, I've come across a lot of posts about latency issues using multiple live feeds and different types of hardware like Matrox and Intensity. 
    My problem is simple and pretty straightforward. Latency on the output video, which doesn't change much with any tweaks on frame rate or video size through Isadora.
    Any ideas on what to do? Am I doing something wrong? I just need one or two simple live feed scenes with not much more happening, so it should really be very simple, right?
    Thanks, 
    Erato


  • Hi,

    Are you talking of latency on the images you capture ?
    If yes, I think most of your latency comes by the fact that you use DV ( with the FW output of the camera ) for capture.
    Using a "real" video output ( like composite or HDMI ) of your camera should give a better result.
    Mehdi 


  • Dear @eratatat,

    I think that the latency is not on the output, but on the input. FireWire has one of the highest latencies of all. I think Isadora's output should, at most, be one frame of delay.

    To see that in action, make a simple patch: connect  a Keyboard Watcher -> Toggle (trigger input), then Toggle's output to Intensity input of a Projector actor. Then just feed a Shapes actor as the source to the Projector.

    Now press the key defined by the Keyboard Watcher actor. You should see the shapes actor toggle between visible and invisible, and there should be nearly zero latency.

    I really thing your source is the issue here.

    Best,
    Mark


  • Tech Staff

    @eratatat

    Next to the Firewire latency problem:
    What we determined when using a live camera pointing at a choirmaster for singers on backstage, watching him on a LCD screen gives much more delay than an old crt monitor, we always have to use crt for low delay. The camera goes directly to the monitor no computer in between.
    So next to the source/camera and computer there can also be huge differences depending on projector or monitors.

    Best
    Michel



  • For live feeds that need to be sync run through a video mixer, not your computer, it is the only way to stay close to lipsync. The different outputs on cameras will also give different delays, many HDMI outputs also have a few frames. LCD tvs can have a few frames too as will projectors especially with high resolution and when not using native resolution. Ideally, cameras with low latency output like SDI with no processing before (EX-1 cams have Mpeg4 processing before the SDI out), directly to a video mixer and to a projector that has the native resolution of the video mixer output. You can get pretty close to lip sync with this kind of setup.

    Firewire has a big lag, (on testing a canopus input no processing or display- just the latency of input to getting it in the computer I got more than 4 frames delay and the canopus seemed a lot faster that any firewire output from a camera.


  • I recently had good performance with an unearthed Mac Pro 2.1 tower and a Backmagic Decklink Duo with 2x SDI in's giving solid performance from two 100' BNC runs. It wasn't perfect but the latency was definitely down to milliseconds. I even added an extra USB webcam and the performance was still solid.

    GPU - Radeon 5770
    20GB - 667mhz RAM
    2.6 Ghz Quad core tower


  • Hi all,

    thanks for your feedback. I'm aware that the output works just fine. 
    Will try to run through HDMI and see what happens. 
    Saying that, tried to connect my Canon 60d DSLR and didn't manage. Any ideas on connectivity with DSLRs and Isadora? 
    Thanks for the help,
    Much appreciated.

  • Tech Staff

    I connected my Canon 600D via the blackmagic intensity shuttle. Worked with nearly no latency.



  • I had some descent luck with the following setup. We used it for a live feed of the Wizard in our production of Wizard of Oz.  Still some lag... maybe 150ms... within tolerances for our application at least.

    Consumer model JVC midi HDMI out to
    Tripp-light HDMI extender (over 150 foot cat 6) to
    BlackMagic Mini Recorder to
    MacBook Pro (2013) to 
    Front projectors
    We also ran a JPG image on a rear projection screen at the same time.


  • Hdmi is still consumer grade material. Reducing latency requires matched compression from camera to izzy. SDI cards from black magic give you this option. Hdmi is also only good for a fraction of the length and the cables cost 10x's more than a bnc cable.



  • Many cameras have on board delay, both those with SDI and HDMI eg, the sony EX-1 has an SDI out that sits after the mpeg encoder in the chain, it has more delay than it should and less picture quality than the sensor records, the panasonic AGAF100 has both SDI and HDMI and they have the same delay and quality.

    The blackmagic recording devices are very low latency (even lower if you capture with the blackmagic SDK). Then there is projector latency (higher resolution means more latency), and processing latency as well. 
    HDMI and SDI carry industry standard signals, ie there is no real compression difference once it is in one of the SMPTE formats. How the signal gets to that state can increase delay, HDMI itself has no more delay than SDI, but many consumer cameras with HDMI out have a large delay. 
    In any pro system if you want a live feed you go through a mixer (good mixers have a few lines of delay only). They are actually not that expensive to use, the cheapest blackmagic HDMI/SDI mixer is under 1k and with some tinkering or third party software you can remote it via OSC. As there are now many 4k models you can pick up some bargains second hand of the earlier HD units. They do require you use a direct camera signal with no processing though, but do support keying if you want to generate an effects layer over live video with no delay.
    Personally I dont like to get on stage without a mixer and that just in case fade to black emergency button, plus the no latency live feed is something I cannot let go of.

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