[mythtv-users] Way out idea on watching same thing in multiplerooms

Chris Ribe chrisribe at gmail.com
Tue Jan 5 03:01:43 UTC 2010


On Mon, Jan 4, 2010 at 7:26 PM, Tortise <tortise at paradise.net.nz> wrote:

> ----- Original Message ----- From: "David Brodbeck" <gull at gull.us>
>
> To: "Discussion about mythtv" <mythtv-users at mythtv.org>
> Sent: Tuesday, January 05, 2010 1:14 PM
> Subject: Re: [mythtv-users] Way out idea on watching same thing in
> multiplerooms
>
>
>
> On Mon, January 4, 2010 4:06 pm, Eric Sharkey wrote:
>
>> On Mon, Jan 4, 2010 at 6:23 PM, Greg Oliver <oliver.greg at gmail.com>
>> wrote:
>>
>>> Even with long hdmi cables or speaker wires, you are still adding
>>> latency just like ethernet would have
>>>
>>
>> No.  Ethernet packets are a store-and-forward technology.  The delays
>> are caused by the hardware in the switches and end points that have to
>> stop, buffer, and analyze each packet, not in the propagation time on
>> the wire.  With analog speaker wire there is none of that.
>>
>
>  This is true, although the delays are still quite short -- in a
>>
> fully-switched network that's not overloaded you're usually talking a few
> milliseconds at most.  This is roughly equal to the delay you'd get by
> standing one meter away from the speaker.
>
>  This is, however, enough time for an analog signal to travel about 800
>>
> kilometers down a speaker wire. ;)
>
>
> _______________________________________________
>
> Which assists me observe what seems the main diversion here, the latency
> for this use is largely irrelevant.  If one person is moving from room to
> room, who cares about a few milliseconds latency?   Even if it were 500
> msecs out I'd not care. (Assumption - each room has its own audio and video
> derived from the client PC in that room)
>
> I feel we have established the latency concerns are real and of no
> significance to this mode of operation.
>
>
Latency is absolutely a significant issue. When it is on the order of
50-500ms, it will cause a horribly annoying echo at any frontends that are
within earshot of each other.  For example, my wife often watch TV
independently in our adjacent bedroom and living room.  The TVs are far
enough apart that sound from one doesn't usually interfere with the other.
If, however, we are watching the same live program, with one signal coming
off the satellite and the other OTA, there is a ~300ms difference and the
echo effect is intolerable.

Without broadcast quality hardware, there will be no synchronization..
>  Period..  And even then, certain architectures must be met..  You
> cannot have motherboard-x, videocard-y, nic-z and expect to accomplish
> *exactly* synchronized video.


The first part is false, the second part is irrelevant.  If you can keep the
various frontends synced to within 30ms or so, everything will sound fine,
and that level of synchronization is certainly achievable with a random
selection of consumer hardware.

It wouldn't be easy to implement or integrate with MythTV, but it is
certainly possible.  That said, it's pretty far down on the list of features
I would like to see added to MythTV.


-chris
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