[mythtv-users] Recording from HDMI

Paul Harrison mythtv at mythqml.net
Wed Feb 22 18:01:19 UTC 2023

On 22/02/2023 17:20, Jan Ceuleers wrote:

> On 22/02/2023 17:51, Mike Perkins wrote:
>> Don't forget that most STBs, like mine, are probably DVRs anyway. Mine
>> has an SSD and actually records as it displays, which means we have
>> pause/rewind/playback functions built in - which is exactly the same as
>> mythtv's live TV function.
>> To get a true idea of any delay introduced by using mythtv, you'd have
>> to compare it with reception directly by a TV[1] which restricts you to
>> OTA[2] or possibly satellite[3], but would provide a baseline.
> The test I described used identical STBs both for watching the TV feed
> in real time and for MythTV's Live TV function. Whether these identical
> STBs support DVR functionality or not is neither here nor there, but as
> it happens they do not.
> But as it happens I also know the group delay we experience on the BBC
> channels: comparing the BBC Breakfast clock to a DCF-77 clock I have
> within view reveals that the BBC signal is delayed by 13 seconds on its
> way to the land of Belgium that is so far, far away.
> Cheers, Jan

Yeah I'm aware of the delays introduced by digital TV what I'm more 
interested in is what sort of delay the LKV373A introduces to things. 
I'm assuming it needs to encode the video and audio which will introduce 
a delay. I have a couple of USB HDMI capture devices and they claim to 
have a 1/3 of a frame delay. So when it detects a HDMI signal it will 
start to output the raw data in about that time. The downside of these 
sort of devices is the data is effectively the raw digital data 
completely un-encoded which for an HD broadcast is a very large chunk of 
data. The positive side is they give a high quality picture with very 
little delay. It means you can play the video in real time and use a 
remote to change channels or interact with the UI without the annoying 
delay you would get with MythTV.

To be clear I don't use these devices with MythTV I use them for another 
project. I'm just curious what sort of delay these type of devices 
introduce and whether I should give one a try (I  could get one to give 
it a try but they appear to cost 3 or 4 times the cost of the USB ones). 
If the delay is to large then they wont work for what I need them for 
which is why I'm asking.

Paul H.

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