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Thread: Black magic to FMLE to wowza to iPad tuning

  1. #1
    Join Date
    Jul 2009

    Default Black magic to FMLE to wowza to iPad tuning

    I'm trying to setup a video streaming council meetings and I've got it working except for a few issues. Some of which I've solved but I'm not happy with my solutions so I'm wondering if anyone has a better solution.

    My setup:
    Video source:
    analog video (NTSC) and balance audio
    Black Magic Mini converter Analog to SDI
    Black Magic Mini Converter SDI to fiber
    1 KM fiber run
    Black Magic Decklink fiber capture card
    Decklink WDM driver
    Flash Media Live Encdoer 3.2
    Wowza Media Server with Transcoder
    iPad (via flowplayer (flash) ipad plugin so basically html5 video)

    A few settings First FMLE does a switch from 720x486 to 640x480. This is to fix the square pixels issue as it seems decklink doesn't compensate for the square pixel conversion. I'm also using 2 mega bit as a bitrate.

            <device>Blackmagic WDM Capture</device>
            <device>Blackmagic WDM Capture</device>
                <keyframe_frequency>3 Seconds</keyframe_frequency>
    Wowza Media Server 3.5.2

    Some key settings
    <!-- in my encoder config --> 
    					<!-- H.264, H.263, PassThru, Disable -->
    					<!-- default, CUDA, QuickSync -->
    						<!-- letterbox, fit-width, fit-height, crop, stretch, match-source -->
    						<!-- <Crop>0,0,0,0</Crop> -->
    						<!-- <SourceRectangle>0,0,320,240</SourceRectangle> -->
    								<!-- horiz: left, right, hcenter - vert: top, bottom, vcenter -->
    					<!-- AAC, PassThru, Disable -->
    And now the issues:
    1. The volume is very quite. I've tested my levels with an SDI tester and I have a good level coming out of the analog converter (according to my video tech) but the volume is very low by the time it gets to playback. I've added a 12 DB gain to the analog converter. This unfortunately means I will be capping my audio and getting distortion even if my audio feels quite. Is there any way to do a volume gain in software? Possibly during the the re-encoding?

    2. The audio in archives fall out of sync with the video on iPads when watching the recordings (this is live-record). It's only noticeable after 10 minutes or more of play. If I jump to a spot in the video the audio re syncs up but it seems that it's not checking its syncing as it plays. Some older videos play fine for long run and they where converted with FFMPEG and use baseline rather than main. Is there any reason to use main? I've switched to baseline to see if this helps (haven't had the ability to test yet). Is there a known issue with iPad audio sync and main profile h264 aac.

    3. I sometimes see bad compression blocking on the video in both flash and iPad. It will often be that the video looks good then goes to a completely blocky blur then over the next 2 seconds clears up and then goes blocky again. I'm not sure whats causing this, I've seen it on a lot of different networks and it doesn't seem to save to the file. I've tried messing with bitrates and such but could not find a better setting that you see above. Any thoughts on what might cause this or suggestions ?

  2. #2
    Join Date
    Dec 2007


    I don't think there is a way to do a software gain on the Wowza Transcoder side.

    Baseline is preferable for iOS and might help in this case. There are some video card/FMLE combos that have sync problems, but that it re-syncs when you seek points away from the encoder, I think. I would try Baseline profile to see if that solves that problem.

    Otherwise, if it is the encoder, this method should show it.

    If the artifacts you see in the live stream are not in the recording, that eliminates the source and the network between the source and Wowza as problems. It is could be network problems between Wowza and the playback client you are testing, or it is possible that this is playback issues with Main profile, another reason to try Baseline.


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