[linux-dvb] Re: replay control in general

[Klaus Schmidinger <Klaus.Schmidinger@cadsoft.de>]

Stefan Huelswitt wrote:
> 
> On 26 Jul 2001 Matthias Weingart <matthias@pentax.boerde.de> wrote:
> 
> > A nice feature - 2x,3x times slower replay - if we make it
> > slower, we also should think to make it faster too (skip some I-frames).
> 
> Yes, this would be an option, too.
> 
> >> I also think that it would be nice to have 2 or 3 speeds for fast
> >> forward/rewind. Currently only I-frames are displayed what should
> >> give roughly 12x speed. I found it difficult to stop at the right
> >> position if searching through a recording.
> >
> > Maybe that is a problem with buffering. It is playing all it have in the
> > buffer, as well after releasing the key, so you will jump to far. A question
> 
> You may be right. If you stops fast-forward there is a small
> delay until replay continues. This may be where the buffers are
> filled.
> 
> >> What if vdr would display every I-frame 4 times -> would give 3x speed;
> >> 2 times -> 6 speed.
> >
> > This is another question: Does vdr play that I frames
> > (1) with a certain (say 25fps) speed or
> > (2) only as fast as it can?
> 
> As I see from the source, vdr is delivering the
> i-frames as fast as possible, but I don't at which speed the
> driver display them.

Yes, VDR delivers the I-frames to the driver at full speed.
That's because if you want to display a single I-frame, you need to
use the 'play_iframe' function, because apparently the DVB card only
starts decoding after it has received a certain amount of data (which
is more that one I-frame).

So the only way I see to implement a "reduced speed fast fwd/back" is
to send the I-frames several times (unless somebody finds a better way
to display a single I-frame, without sending it several times...).
However, sending an I-frame more than once may cause a jerking effect.
This can be seen on recordings from some channels when you set an editing
mark in replay mode (key '0'), jump to that mark (key '7') and then move
it around (keys '4' and '6'). Sometimes you can see objects jerking around
here, which I would assume results from the I-frame being sent several times
in order to fill the MPEG decoder's buffer.

Klaus
-- 
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Klaus Schmidinger                       Phone: +49-8635-6989-10
CadSoft Computer GmbH                   Fax:   +49-8635-6989-40
Hofmark 2                               Email:   kls@cadsoft.de
D-84568 Pleiskirchen, Germany           URL:     www.cadsoft.de
_______________________________________________________________


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