[vdr] Re: vdr at dbox2

[Andreas Oberritter <obi@linuxtv.org>]

On Fri, 2004-02-27 at 23:30, Carsten Koch wrote:
> >>3) The DVB driver on the dbox does not provide the necessary functions
> >>    for any of the trick modes (Fast Forward, Fast Reverse, Slow Motion).
> > 
> > 
> > They never will for two reasons:
> > a) The decoder does not support either of these features.
> 
> Of course it would be nice to have hardware support for these,
> but is that the only chance?
> I mean, obviously the software can control the sequence of
> frames sent to the controller, so at least for FF/FR it could
> send only I-frames or only every Nth I frame.
> 
> Regarding slow motion I do not know. I guess it will not yield
> the desired results to replicate P- or B- frames?  ;-)
> However, slow motion by replicating I-frames often enough
> may be better than nothing.
> 
> If I had enough time, I would try that all out inside VDR.
> 
> 
> > b) The network interface is too slow for real fast forward.
> 
> Are you sure? I have never calculated that.
> Note that VDR does know the file offsets of all I-frames
> (that information is stored in the index.vdr file), so it
> would only have to read I-frame data over the network for FF/FR.
> How big is a typical I-frame?
> At 10 Mbit/s and 25 I-frames per second the theoretical
> maximum size would be < 50 kilobytes.
> If I-frames can get larger than that, one might play back
> every (Nth) I-frame twice.
> Does any of that sound realistic to you?

Isn't that still picture display what you're describing? You can do that
for sure, but that's not fast forward etc. at driver level. You would
need to implement the still picture ioctl()s though.

Btw. it is more like 5MBit/s. It's half duplex and occupies the CPU
quite a lot unlike PCI cards capable of bus mastering.

Regards,
Andreas



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