Bob() with NO resizing

[Zalkalin]

I'm encoding an interlaced 25 fps DVD, and I'm playing around with various methods of deinterlacing.

In my avs script I'm using SeparateFields after loading the video, so I end up with 50 fps, half-height video that jumps up and down. So I want to 'bob' it, and AviSynth does have a function to do that, but what annoys me is that it changes the height of the frames. I want to keep the frames half height, and resize the video on playback. What can i do?

I could load everything into VirtualDub and use it's bob filter which does what I need, but that involves messy color space conversions and whatnot. I'd like to use fast recompress if possible.

Suggestions?

[hakko504]

In the AVIsynth documentation (http://www.videotools.net) it is mentioned that bob has a height parameter that could be useful:bob(height=288) #to keep PAL at half height

[Zalkalin]

bob(height=288)I noticed that parameter, but what worries me is that the resizing somehow might degrade the quality a bit, even though the picture is resized to the same height. I don't know. Could someone explain?

Also I suspect I might lose some performance, due to the resizing algorithm being invoked.

[mrwho]

In my avs script I'm using SeparateFields after loading the video, so I end up with 50 fps, half-height video that jumps up and down.

By talking about this problem, would be nice if somebody could make a script-able version of the internal "field-bob" plugin of Virtualdub

somehow sad that only avisynth can separate-fields and only virtualdub can field-bob... :(

Or am i wrong ? :confused:

[Wilbert]

On Donalds homepage http://sauron.mordor.net/dgraft/mine.html you can find the filter "SmartBob" and there does exist a script for that. See VirtualDub filters import file v1.3 (http://forum.doom9.org/showthread.php?s&threadid=23804).

[Zalkalin]

Here's what the dev had to say on the field bob issue:

----------------------------------------------------------
>So is there a way to do this natively in Avisynth?

No, not that I know of.

>If no, is there any chance of it being implemented?

I am not planning it.
----------------------------------------------------------

:(

[mrwho]

>If no, is there any chance of it being implemented?
I am not planning it.

Sad to hear :(

Well, perhaps somebody with C++ Experience will transform the virtualdub-version into a avi-synth version (under the GPL of course)...

[Richard Berg]

It's impossible to bob without resampling. The adjustments you need to make are a quarter-pixel in each direction, which generally means you need to interpolate up to full frames. You could do it "in-place" with an offset filter of 1/2 pixel, but it's still resampling.