[vdr] Re: Idea: Change DVB card while recording

[huels@iname.com (Stefan Huelswitt)]

On 28 Oct 2001 Carsten Koch <Carsten.Koch@icem.de> wrote:

> 1) would even a single frame be lost in the process of simply 
>    switching from one card to another?
>    After all, switching from 001.vdr to 002.vdr does not loose
>    frames either.

This is different because there is no gap when switching files,
vdr just starts to write to another file without loosing any
data.

When changing to a different card, first the recordbuffer has to
shutdown, then tune the new card, start recording. I estimate
that this cost at least 2 seconds, which are lost. I think this
is noticeable in most cases.

> 2) Even if a whole GOP (12 frames) is lost, would you even
>    notice?
>    Make the following experiment: Record a few minutes, the cut
>    out one GOP. Play back the original and the cut version.
>    Remember that a GOP is less than a quarter of a second. 

At 25fps a 12-frame GOP is (nearly) a half second. And did you
noticed that you have square picture distortions just after the
cutting point in most cases?
I think this is because B- & I-frames rely on past frames for
their incremental picture changes.

-- 
Stefan Huelswitt
huels@iname.com  | http://home.pages.de/~nathan