Audio stream in test card input

Discussion about this major DATV Project. See https://wiki.batc.org.uk/The_Portsdown_Transmitter
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mccla5214
Posts: 61
Joined: Sun Sep 05, 2021 1:45 am

Audio stream in test card input

Post by mccla5214 » Sat Sep 11, 2021 2:28 am

is there anyway to have an audio stream when using the test card input source. I'm trying to have a 1 KHz. tone transmitted at the same time that I'm displaying the test card input.

Getting great sound when in PiCam input but nothing in test card.

Thanks,

Mike

IZ7PDX
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Joined: Mon Jan 31, 2022 7:55 pm

Re: Audio stream in test card input

Post by IZ7PDX » Mon Feb 21, 2022 8:03 am

Also I have wondered several times why it is not possible, I suppose it is a bug that will be fixed soon!
The tone is not transmitted even when selecting EasyCap (video looks good) and other similar circumstances.

G8GKQ
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Re: Audio stream in test card input

Post by G8GKQ » Mon Feb 21, 2022 9:44 am

Hi

When I was implementing the Test Card H264 transmission feature on the Portsdown (which actually puts a testcard on the screen, and then transmits a screen capture), I found that it was not easily possible to reliably include audio on that transmission. That seems to be caused by the way that I have used F5OEO's H264 encoding/transport stream creation software. I spent a day trying to solve this and decided that my time could be better spent on other things.

The test tone on MPEG-2 encoded transmissions is generated in a different manner, which does not easily integrate with H264 transport stream generation. So please think of the availability of a test tone on MPEG-2 transmissions as an added feature, rather than a feature missing (or, worse, as a bug) in H264 transmissions.

The code is all available on GitHub, and I would be pleased if someone could offer me solutions to implementing these features. Referring to their omission from the current code as a bug is not helpful.

Dave, G8GKQ

g0mjw
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Re: Audio stream in test card input

Post by g0mjw » Mon Feb 21, 2022 2:17 pm

Hi Dave

One potential solution is to pre-generate a proto-transport stream and send that with ffmpeg - so ffmpeg is only doing multiplexing rather than encoding. It could also do H265 or whatever if it doesn't need to encode. There would need to be several copies at various symbol rates. As long as it is less than the transmission rate nulls could be added in the multiplexer.

Mike

IZ7PDX
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Joined: Mon Jan 31, 2022 7:55 pm

Re: Audio stream in test card input

Post by IZ7PDX » Thu Feb 24, 2022 9:07 pm

Ok Dave, thank you for the answer, it's all clear now! I did not mean to denigrate the incredible work you have done, congratulations because many things work very well. As there were no indications, it was not easy to understand that the audio tone transmission function with the Test Cards is not implemented. We await suggestions best 73 Luigi.

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