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SRT Connection Jittery
Rank: Member
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Joined: 12/14/2019(UTC) Posts: 23  Location: Atlanta
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Hello all,
We are running some trials with SRT and VMix in order to gain some valuable knowledge to step up our remote operations game.
The current issue that we're facing is that an incoming SRT stream from a video server to VMix is showing lots of jitters and skipped frames.
The SRT connection from the server to the same computer is solid because it has been ingested into VLC with perfect smoothness while Vmix continued to be choppy simultaneously.
The things we've tried so far with no luck:
- Swapping the Caller/Listener for each side
- Rendezvous Mode between Server and Vmix
- Lowering and Raising the bitrate of the video
- lowering and raising the latency of the SRT instance
- restarting VMix
- restarting the PC
The SRT output is perfectly fine and smooth. Little to no issues outputting SRT.
Any help is appreciated. Thanks!
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Rank: Administration
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Joined: 1/13/2010(UTC) Posts: 5,216  Location: Gold Coast, Australia Was thanked: 4312 time(s) in 1525 post(s)
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 1 user thanked admin for this useful post.
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Rank: Member
Groups: Registered
Joined: 12/14/2019(UTC) Posts: 23 Location: Atlanta
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Interesting. Today we had a similar setup, but with a TSUDP stream with the same jitter effects.
It seems to worsen as time goes on.
The same streams that are choppy as Vmix inputs are perfectly fine on any other player on the same hardware at the same time.
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Rank: Administration
Groups: Administrators
Joined: 1/13/2010(UTC) Posts: 5,216 Location: Gold Coast, Australia Was thanked: 4312 time(s) in 1525 post(s)
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Most other players have a very high buffer by default, VLC has 1 second (1000ms) for example.
So for a true comparison you would need to set the buffer in vMix this high as well.
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Rank: Member
Groups: Registered
Joined: 12/14/2019(UTC) Posts: 23 Location: Atlanta
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Originally Posted by: admin  Most other players have a very high buffer by default, VLC has 1 second (1000ms) for example.
So for a true comparison you would need to set the buffer in vMix this high as well. Hello, I appreciate the response! I just tried raising the buffer to 1000, but continued to see unreasonable frame drops. I also just raised it to 5000 and 10000 just to see if at any point it's a stable connection, but I am currently seeing ~12 dropped frames per second at 10000ms buffer.
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Rank: Administration
Groups: Administrators
Joined: 1/13/2010(UTC) Posts: 5,216 Location: Gold Coast, Australia Was thanked: 4312 time(s) in 1525 post(s)
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There are two buffers to consider, Decoder Delay and the SRT buffer itself.
Also note that frame drops may be normal if the source is sending a different frame rate to vMix.
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Rank: Member
Groups: Registered
Joined: 12/14/2019(UTC) Posts: 23 Location: Atlanta
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Originally Posted by: Plamen Originally Posted by: admin Most other players have a very high buffer by default, VLC has 1 second (1000ms) for example.
So for a true comparison you would need to set the buffer in vMix this high as well. Hello, I appreciate the response! I just tried raising the buffer to 1000, but continued to see unreasonable frame drops. I also just raised it to 5000 and 10000 just to see if at any point it's a stable connection, but I am currently seeing ~12 dropped frames per second at 10000ms buffer. Ok, my test must have had a fault of some sort. I was able to smooth out the frame drops to a acceptable level by increasing the decoder delay. I also successfully used the VLC stream decoder in Vmix to take in the SRT streams with minimal frame drops. Both of these options increased latency dramatically though. In order to smooth out frame drops, the glass to glass latency of the video distribution server to a Vmix instance local to that server is almost 1 or 2 seconds longer than the latency from that same server to an off-site vmix instance which common sense makes me believe should not be occurring. By bypassing the video distribution server, I noticed that the same problem would arise with incoming SRT streams. Extremely choppy unless there is an unrealistic decoder delay. This leads me to believe that Vmix's decoder (or vmix in general) does not get along with the enterprise hardware in this machine. (Xeon E5-2690 v4 + Tesla M60) All our tests on consumer hardware have been amazing and vmix has been rock solid in all fronts.
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