[linux-dvb] Re: HDTV & DVB / VDR (dscaler ..)

[Emil Naepflein <Emil.Naepflein@philosys.de>]

On Thu, 10 Jan 2002 16:17:01 +0100 (CET), <mocm@convergence.de> wrote:

> Emil Naepflein writes:
>  > Does the MPEG stream transmitted bei DVB contain the interlace flag
>  > identifying fields that belong together just like on DVD?
> 
> Probably depends on the encoder of the channel provider. We don't
> change anything about the elementary stream.

This is all AFAIK:
I did never analyze the stream, but do both interlaced fields always
come separate or does it happen that one frame is transmitted with the
repeat flag set. This is what happens on DVDs. They encode the full
frame and send it only once with the flag set. The decoder then sends
the two separate interlaced frames to the video chip. This information
is also used with most of the software and hardware decoders for DVD to
produce progressive output. They just combine the right frames and you
get 50 Hz progressive, or for NTSC 60 Hz progressive.

> It depends on the driver. The bt848 driver puts the half frames into
> separate pictures, if the size is smaller than half the TV resolution.
> I haven't checked what the saa7146 does in that case. 
> If your graphics card supports Xv than xawtv uses the hardware scaler
> of the card to scale the picture to full screen size. In this case you
> may still get a line running through the picture, because v4l device
> and graphics card are not in synch.

> Maybe you may want to check out DirectFB, the developers were working
> on synching the v4l output to the output of the graphics card. They
> had it working for Matrox cards, but I don't know if they have other
> cards working and if it is included in the latest version.

The sync is another problem. This may cause the tearing effect seen on
older XGA DLP beamers. Here you may see parts of two frames concurrently
on the screen. This can be fixed by proper buffering.

But before this becomes relevant it is important to combine the right
fields  to avoid this nasty combine artefacts.

Emil


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