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SRT Input Dropping Frames
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Anyone else noticed with SRT inputs they drop frames when fed by SRT hardware encoders. Haivision MakitoX vMix drops maybe one or two per 2 or 3 minutes so this is not a problem. Kiloview E1 vMix drops multiple frames per minute resulting in unusable video. If I bring in the same SRT streams via the vMix VLC module (yes this works) then no frames are dropped so it seems the issue is in the vMix decoder.
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What is "vMix VLC module"?
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 1 user thanked lestra for this useful post.
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Originally Posted by: nakedeye  If I bring in the same SRT streams via the vMix VLC module (yes this works) how do you bring it to vMix with VLC?
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Joined: 1/13/2010(UTC) Posts: 5,208 Location: Gold Coast, Australia Was thanked: 4288 time(s) in 1520 post(s)
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Hi,
Increase the Decoder Delay setting on the SRT input in vMix until the video is smooth.
Some encoders do not correctly pace their frame rates, so this option is available to compensate for that.
Regards,
Martin
vMix
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1 user thanked admin for this useful post.
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Rank: Advanced Member
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Thanks Martin! I will try that and see if it works. The problem actually seems to be only with 720p footage and 1080p seemed fine in short tests. We ended up using SRTMiniServer on an AWS instance to feed vMix on the same VPC with no dropped frames at all.
@lestra @xaver If you add an input in vMix and select the Stream/SRT option then under Stream Type choose the VLC option and type in the SRT URL of your caller this will bring in the SRT stream to vMix.
Cheers, Dave
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Joined: 12/14/2019(UTC) Posts: 23  Location: Atlanta
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Originally Posted by: nakedeye Thanks Martin! I will try that and see if it works. The problem actually seems to be only with 720p footage and 1080p seemed fine in short tests. We ended up using SRTMiniServer on an AWS instance to feed vMix on the same VPC with no dropped frames at all.
@lestra @xaver If you add an input in vMix and select the Stream/SRT option then under Stream Type choose the VLC option and type in the SRT URL of your caller this will bring in the SRT stream to vMix.
Cheers, Dave Did you ever end up diagnosing the issue with the SRT decoding? We're experiencing similar issues and the only solution we've found is VLC decoding. The vlc decode also starts dropping frames after 6 hours though.
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Rank: Member
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Joined: 12/14/2019(UTC) Posts: 23 Location: Atlanta
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Originally Posted by: admin Hi,
Increase the Decoder Delay setting on the SRT input in vMix until the video is smooth.
Some encoders do not correctly pace their frame rates, so this option is available to compensate for that.
Regards,
Martin
vMix Is it possible that a Vmix SRT Encoded stream might experience this symptom? Does the type of hardware effect whether or not Vmix can correctly pace it's frame rates? Also Martin, could you elaborate more on how the Decoder Delay works? Searching through the SRT Alliance Deployment Guide shows no indication of decoder delay information anywhere. Is there a certain formula or rule-of-thumb to calculate what the decoder delay should be set to? Thanks!
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Rank: Advanced Member
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The decoder delay should allow some additional time for all the data packets to arrive prior to decoding. Start with 100ms and work up until the dropped frames disappear. We noticed that in vMix a 720p/50 stream from a Kiloview E1 Encoder needed 250ms in the decoder delay setting to remove dropped frames and 100ms for Haivision MakitoX. At 1080p/50 we did not need any delay but set to 100ms for insurance which may or may not have been necessary. I think different Encoders have different ways of working so not everything is equal. It is a good option to have and SRT MiniServer has this setting also.. so very useful.
We have successfully completed two sessions of basketball with just the camera operators at the venue. vMix was hosted on AWS in Sydney and SRT streams were converted to NDI so we could use replay. Be nice to have SRT as a replay source directly.
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