[LAU] AVSynthesis videos on-line

[Florin Andrei]

Dave Phillips wrote:
> 
>     http://www.vimeo.com/groups/1156/videos/1295336
> 
>     http://www.vimeo.com/groups/1156/videos/1295510
> 
> Image transformations/animations by the OpenGL shading language (GLSL), 
> sound by Csound5, using Jean-Pierre Lemoine's AVSynthesis.

Very nice. I tried this software a while ago but it was a pain to 
install. Hopefully that will change.

A few observations:
You render 800x600 frames (4:3) yet the active area is only 800x340. 
That's a very nice cinema-like 2.35:1 format, but it's a waste of space 
in a 4:3 frame - the letterboxing is just wasting precious bandwidth in 
the video stream and the image quality decreases. Yes, it's just black 
pixels, but even those don't come 100% for free.

Never letterbox anything while making a video that will be played on a 
computer (a "square pixel" video). Let the player worry about that, it's 
the player's job not yours.

If you create a video that will be played on computers (such as an AVI 
with video encoded as MPEG4 or something like that), use square pixels, 
and either render 800x600 full frame (4:3 image format), or 800x340 if 
you prefer the cinema format, but again full frame, no letterboxing. Or 
render 800x450 full frame if you want 16:9.

mjpegtools on Linux give you a full processing chain that can be used to 
tweak the image and remove letterboxing, if you can't convince 
AVSynthesis directly to not letterbox.
Similarly, AviSynth on Windows (and on Linux under WINE) can do the same.

If you make something for a standalone player, let's say an MPEG2 file 
that will be authored as DVD, you can still render full frame if you 
choose one of the accepted image formats: either 4:3 or 16:9.

In that case, just create the master images with AVSynthesis at either 
4:3 or 16:9 format for the active area, remove letterboxing in an 
intermediate step, then create an MPEG2 stream at 720x480 and specify in 
the encoder that you're actually using the 4:3 or 16:9 image format and 
let the player and the display deal with image scaling and letterboxing. 
That's called an image with "non-square pixels" and is very common - all 
DVDs use that.

If you want other image formats on DVD, you still have to make it 
720x480, specify a default image format (4:3, 16:9) that's closest to 
the one you desire, and then you will have to letterbox a little bit. 
Usually, the commercial 2.35:1 movies on DVD use the 16:9 MPEG2 image 
format (actual resolution: 720x480 with non-square pixels) and letterbox 
the image a little bit.

If you go HD, you can again use square pixels - just begin with a 
1920x1080 active area and use square pixels all the way to the end (an 
AVCHD file or a BD-R).

-- 
Florin Andrei

http://florin.myip.org/