[vdr] How to convert a JPEG image to an I-frame?

Reinhard Nissl rnissl at gmx.de
Thu Dec 27 14:53:04 CET 2007


Hi,

Klaus Schmidinger schrieb:

> When I display field_test.mpg via DeviceStillPicture() on my FF DVB card
> I see a picture that has a top and a bottom half that rapidly flicker
> black and white (top black, bottom white and vice versa).

I've just verified this behavior on my EPIA VDR in the living room
(which is connected to a 50 Hz TV set) by taking a photo.

The photo shows that the white lines are quite thick -- there is no gap
between them. And the black area is totally black, i. e. the white area
from the previous field has vanished already.

> After like half a second the picture gets static, and the top half is
> solid black, while the bottom half is solid white.

I had a look into the FF card's driver implementation. The driver simply
repeats the still image data for some time. And from your report I
guess, that the FF card automatically displays two fields for each frame
it receives. When the driver stops sending frames, the FF card displays
the last field forever.

I also had a look into the hardware specification. It seems to me that
the chip can be switched to a mode where it toggles between the fields
automatically. But my coarse understanding of the driver tells me, that
the driver doesn't make use of it.

> I never see anything like the field_test.png you posted (with alternating
> black and white lines).

So although xine displays the image on a screen of resolution 720x576 in
both cases, it looks like the TV is showing 50 fields of resolution
720x288 while the PC monitor (on my desktop) shows 85 frames of
resolution 720x576. Although the TV should weave the two fields, this
won't result in a frame of resolution 720x576, as the lines are too
thick and the previous field vanished already, so this seems to be the
reason why horizontal lines of thickness 1 flicker.

Looks like the only way out of this is to scale the image to 720x288,
double the lines and encode it as 720x576.

Bye.
-- 
Dipl.-Inform. (FH) Reinhard Nissl
mailto:rnissl at gmx.de



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