How do I use VMix with Portsdown 2019?

Discussion about this major DATV Project. See also https://wiki.batc.org.uk/The_Portsdown_Transmitter
g0mjw
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Re: How do I use VMix with Portsdown 2019?

Post by g0mjw » Tue May 14, 2019 6:01 am

I am using OBS, not VMIX but the difference is I am not using the Portsdown. I am using a Nvidia Jetson Nano. The Portsdown will work and many are using them but the PI does not have the processing grunt of the Nano.

If you generate your transport stream locally on your PC, the Portsdown will transmit it. I do that to, with a PI and with a LimeNetMicro. PCs usually have much more powerful CPUs than in the PI and can encode the video more efficiently. This encoding is especially important at low symbol rates.

Mike

G4WIM
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Re: How do I use VMix with Portsdown 2019?

Post by G4WIM » Tue May 14, 2019 11:07 am

Hi Mike,

must admit I'm a bit puzzled.

I get it about processing power etc which is why my main PC is an X99 6 / 12 cores running at 4.2GHz with 32G ram - so no shortage of CPU cycles etc.

However as per the instructions I'm running ffmpeg locally on the PC and looking at the batch file I was under the impression that ffmpeg was doing all the heavy lifting and thus all the rpi has to do is handle the transport stream.

If I'm understanding you correctly, this is not the case and there's some sort of bottle neck in the rpi when handling external trafffic via the IPTS encoder function - at a guess converting the TS to IQ signals and so onto the USB to drive the Lime might be issue ?

Regards Tim

g0mjw
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Re: How do I use VMix with Portsdown 2019?

Post by g0mjw » Tue May 14, 2019 11:44 am

Hi Tim

That's right. All the heavy lifting on the PC, Transport Stream sent to the PI to deal with the encoding and modulation. That's how I did it.

There is another way, which is to send the video and audio via UDP, or some other means, and have it encoded on the PI. With the Nano, I generate a UDP Transport stream on my PC (or with an LK373a) at high rate e.g. 8Ms/s in H264 and send it to the Nano which transcodes to whatever format I am sending. The Nano can do that, the PI less so.

If you are having problems with the batch file, what are they? You probably have a higher video bit rate or audio bit rate than fits into the TS. Alternatively something not right with the CODEC. This is compounded by constant bit rate encoders not really being constant. The H265 encoder is worse for this than the H264 one.That's covered by the twiddle factor in Charles' Express software and by a similar scaling in the script. E.g.:

set /A VIDRATE= (%TSBITRATE% - 50000 - %audiobitrate% * 125 /100) * 80 / 100

So you could start by making that 60/100 and see if things improve.

Mike

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Re: How do I use VMix with Portsdown 2019?

Post by G8GKQ » Tue May 14, 2019 2:04 pm

Tim, John and Mike

If this is with the LimeSDR, I think that your problems might be associated with the issues that I am having with making it work properly with other video sources. viewtopic.php?f=103&t=6070#p19583.

I did not test IPTS in as it is not a core mode. Once I turn the rest of this matrix green, I'll get have a go at making IPTS in work properly.

Dave, G8GKQ

G4WIM
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Re: How do I use VMix with Portsdown 2019?

Post by G4WIM » Tue May 14, 2019 2:11 pm

H Mike,

I've followed this wiki https://wiki.batc.org.uk/Feeding_Video_ ... _from_vMix

which calls out a batch file which I've edited to contain my callsign and ip address of the RPI - but sadly I get the results previously mentioned.

It does seem to indicate a video bit rate / TS problem or CBR issue as you mention.

Looking at your line of code :


set /A VIDRATE= (%TSBITRATE% - 50000 - %audiobitrate% * 125 /100) * 80 / 100

doesn't seem to work within the batch file due to variables TSBITRATE and auiobitrate not having been defined, also the VIDRATE values for various FEC's have been calculated to take into account the TS bandwidth and included in the batch file.

The puzzle for me is why the RPI chokes - considering it works for others and I'm running on a rpi 3 B+ with a class 10 MMC.

Obviously I'm missing something here - just not sure what ......

EDIT just saw Dave's response - looks like I'm the 'corner case again' and expecting too much ! Strange that others have used IPTS and the Lime mini with no issues though. Several locals with identical set ups have no problems at all, but as usual I'm not blessed :-)

Regards Tim

g0mjw
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Re: How do I use VMix with Portsdown 2019?

Post by g0mjw » Tue May 14, 2019 5:37 pm

Tim - you are assuming that line is from the wiki batch file - it is not, it is from the one I pasted earlier in this thread and the variables are set in the script. Somewhere you will have a scaling factor for the bitrate - e.g. 80 / 100 as it was above. Reduce that.

The Wiki is from 2017 and out of date. I did not write it but perhaps the files need to be removed to avoid confusion.

Mike

G4WIM
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Re: How do I use VMix with Portsdown 2019?

Post by G4WIM » Tue May 14, 2019 6:35 pm

thanks for putting back on track Mike - I'll take another look.

Regards Tim

G7JTT
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Re: How do I use VMix with Portsdown 2019?

Post by G7JTT » Tue May 14, 2019 8:54 pm

Thanks for the info dave, I have had Vmix working to a fashion work for a while then drops out. But not so successful with OBS just get loads of ffmpeg errors. I will have another go tomorrow based on the most reliable settings from your chart.

Cheers John G7JTT

P.s now looking at another way of using OBS, hdmi to composite video adapter and use the HDMI output on the laptop and feed it into the easycap on the Pi at least that should work 🤞

G8GKQ wrote:
Tue May 14, 2019 2:04 pm
Tim, John and Mike

If this is with the LimeSDR, I think that your problems might be associated with the issues that I am having with making it work properly with other video sources. viewtopic.php?f=103&t=6070#p19583.

I did not test IPTS in as it is not a core mode. Once I turn the rest of this matrix green, I'll get have a go at making IPTS in work properly.

Dave, G8GKQ

G4WIM
Posts: 257
Joined: Thu Jan 29, 2015 8:36 pm

Re: How do I use VMix with Portsdown 2019?

Post by G4WIM » Wed May 15, 2019 2:53 pm

Hi Mike,

using the vmix script you posted has resulted in vmix playing nicely at 333ks with good audio sync and little delay - but does freeze the pi after a while.

So being a glutten for punishment I've ordered a jetson nano which doubtless will result in a different crop of problems.

Couldn't seem to get the vmix script to work with OBS despite setting vmix=0. Not sure what the OBS output settings should be to work with the script.

I was adjusting the obs output recording settings to send the output to udp address of the pc - but the batch file complained about input mismatch.

Regards Tim

G3YQC
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Re: How do I use VMix with Portsdown 2019?

Post by G3YQC » Wed May 15, 2019 3:08 pm

Partial success! – using the new batch file Vmix_PI.bat from Evariste available here: Vmix_PI.zip (many thanks Evariste and G0MJW for pointing it out) I can now transmit stable video and audio for up to about 4mins before losing lock.

I set up vMix in the normal way and clicked the External button to start the TS.

Choosing a Symbol rate of 333Ks and FEC 1/2 the transmitted picture and audio through the Portsdown 2019 was stable on the MiniTioune for around 4min’s or so before losing lock, and on the MiniTioune the four TS LED’s turned red, as did the error box.

Symbol rates of 250 and 333Ks and various FEC’s all worked similarly. Choosing more or less video definition made no difference. Choosing 1000Ks SR did not achieve a lock at all.

It seems that vMix will output from the PC to the Portsdown OK but the question remains – why is the transmitted video/audio only lasting for around 4min’s before losing lock on the receiver?

73 John

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