[vdr] channel-change-prediction, doable? stupid idea?

Torgeir Veimo torgeir at pobox.com
Fri Jan 23 16:21:25 CET 2009


On 23 Jan 2009, at 23:55, Udo Richter wrote:

> On 21.01.2009 19:33, Gerald Dachs wrote:
>> Assumed I have 2 free Tuners and I zapp through the channels of one
>> tuner. Would it be possible to tune the 2. tuner to the same time to
>> the after next channel in change direction, so that for the next
>> channel change in the same direction it would be possible to
>> channge to the 2. tuner instead of changing the channels of
>> the 1. tuner
>
> Channel switching delay is caused by two delays: First, the time to  
> tune
> and lock the new transponder, second, the time till the next  
> compressed
> stream starting point (I-Frame or audio syncword) is reached. This
> second time can be up to a second by its own.
>
> To get instant switching, you would have to also decode the second
> stream in the background, so that the current frame is available the
> moment it is needed. Or you can buffer the last GOP of the stream  
> and go
> back to that point on channel switch. You would have to ring-buffer up
> to one complete GOP permanently in memory to keep the delay from  
> there on.
>
> Both things are tricky to implement, require work on the output  
> devices,
> and are probably not worth the effort.


Depends if you mean "not worth the effort" == (salary paid developer  
to implement feature - extra income due to extra sales) or if we're  
talking some hacking away on it for the heck of it. :)

With vdpau and other accelerated output methods on generic opengl  
capable hardware becoming available, it can easily be seen  
advantageous to be able to fetch a new transponder while the old is  
still in use, to do picture in picture or other fancy effects. The  
frontend could be more intelligent, and just request channels as it  
see fit, this is also what's needed in order to implement multi- 
frontend setups with vdr. The recording subsystem can fetch as many  
channels as it needs as long as there is enough free tuners, so why  
shouldn't the frontend be able to do it as well?

-- 
Torgeir Veimo
torgeir at pobox.com







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