Lean DVB and Stream audio.

Discussion about this major DATV Project. See https://wiki.batc.org.uk/The_Portsdown_Transmitter
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M5TXJ
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Lean DVB and Stream audio.

Post by M5TXJ » Tue Jul 24, 2018 9:17 am

Hi all,
Looking at adding an audio amplifier to my Portsdown, do I connect to the Pi 4 pole 3.5 or the USB dongle for audio from Lean DVB and the stream receiver?
Thanks Dave.
...are you sure I can't use a pair of 813's?... :shock:

G7JTT
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Re: Lean DVB and Stream audio.

Post by G7JTT » Tue Jul 24, 2018 11:28 am

The Pi A/V 3.5mm port at the moment

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M5TXJ
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Re: Lean DVB and Stream audio.

Post by M5TXJ » Tue Jul 24, 2018 11:35 am

Thanks

73 Dave
...are you sure I can't use a pair of 813's?... :shock:

G1BVI
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Re: Lean DVB and Stream audio.

Post by G1BVI » Wed Jul 25, 2018 9:40 am

Whilst flicking through the streams last night on the Portsdown TX I came across an analogue image being broadcast.
I watched in silence for a few minutes expecting to see a call sign.

I then switched on shack computer and connected to the same feed so I could hear the audio which turned out to be a regular net.

What I noticed was that the Portsdown image lag got greater with time by a very large degree.

I understand that this is a Transmitter and not really designed for viewing a stream in real time, but having seen this thread asking about audio out for the stream on the pi I was wondering how it actually sounded having seen how the video lag was getting progressively greater wrt the main computer.

73

Nick

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Re: Lean DVB and Stream audio.

Post by G8GKQ » Wed Jul 25, 2018 11:05 am

Hi Nick

The stream display delay at start-up is about 4 or 5 seconds greater than viewing on a PC. I hadn't noticed it increasing over time, but will monitor it.

I was watching G8LES on the GB3HV net last night and his audio sounded OK on my Portsdown, but again I haven't listened for long periods.

The Portsdown outputs stream audio on the AV socket. With no USB audio dongle connected, it will also output RTL-FM on that socket. However, if you have a USB Audio dongle connected, RTL-FM audio goes to the USB Audio dongle.

This is because use of the RPi AV socket precludes Portsdown transmissions until after a reboot (a complex driver issue that I have not been able to solve). However, I could not get the stream audio to work the the USB audio dongle - hence the different behaviour.

Last point: LeanDVB does not decode audio (yet), just video.

Dave

G1BVI
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Re: Lean DVB and Stream audio.

Post by G1BVI » Wed Jul 25, 2018 3:23 pm

Hi Dave
That was the same feed I was watching.
I shall have to connect some kind of amplifier and speaker to the Portsdown and try it out myself.
I realise there is a couple of seconds before feed starts but it drifted apart quite quickly.

When the PC footage had finished and it had moved on to something else G*LES? was still sitting down looking at the camera.:-)

If its cooler tonight I might get down under the bench and access the pc speaker plug to transfer to the pi.

73

Nick

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Re: Lean DVB and Stream audio.

Post by G8GKQ » Thu Jul 26, 2018 11:09 am

Nick

I have done some investigation on this. It appears to be related to the frame rate of the stream being viewed. I had been testing with Portsdown-generated video streams, which are 25 fps. These do not display increasing lag on the Portsdown stream Viewer.

The GB3HV stream does display increasing lag. I don't seem to be able to cure this problem on the Raspberry Pi. I will ask the keeper of GB3HV to check the frame rate - I suspect that it is 30fps.

Dave, G8GKQ

G1BVI
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Re: Lean DVB and Stream audio.

Post by G1BVI » Thu Jul 26, 2018 10:00 pm

Hi Dave
I was watching another stream last night and was going to report that it now seemed to be working...
Then I watched HV and there was the lag hi hi.

Still got no audio output on the pi as the speakers are USB but glad to see its not my hardware.

73

Nick

g8gtz
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Re: Lean DVB and Stream audio.

Post by g8gtz » Fri Jul 27, 2018 7:38 am

Interesting - as keeper of GB3HV I can that we may have a bit of a frame rate issue...

Adobe encoder reports it's running at 24.92 fps (not as much as I thought) and we do have an issue in that the aspect ratio creeps out so there's something strange going on. There's a TBC in front of the encoder and I would if that is suspect....

We are intending to replace it with a Portsdown streamer sometime and it will be interesting to see if that fixes it.

73
Noel - G8GTZ

G1BVI
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Re: Lean DVB and Stream audio.

Post by G1BVI » Fri Jul 27, 2018 11:21 am

I just think its amazing how computing power has developed in the last 50 tears.
Even Jules Verne or Isaac Asimov did not forsee the Portsdown :-)
73
N

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