Re: Video4linux-list digest, Vol 1 #254 - 11 msgs

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> Certainly Broadcast isn't as good for grabbing; but is great to use for 
video
> editing (specially for QT movies), and can grab in stereo.

> I'm grabbing using Uncompresed RGB (maximum quality). That's a LOT of hard
> drive, but the quality is *AWESOME*, and I think the CPU works less if the
> grabbing does no compression.
> I'm going to try with JFIF  with various qualitys. Image/Sound Quality is my
> motivation, that's why I stop using mp1e (even with a bitrate of 10000000,
> the reencoded MPEG ends with a very poor quality). The MPEG resulting of
> encoding QT movies (in uncompressed RGB) have a very good qualtity, even 
with
> a bitrate of 1152000 or 2500000.

I see. I'm just playing around with bcast2000. 
As a last resort you might just grab jpegs (that gives thousands of them in a 
few minutes, and streamer seems to be even faster then), and in parallel, 
record a 16 bit stereo wav-file (also with xawtv, of course). 
bcast can import jpeg-pictures, and you might render your high quality 
QT-movie from them along with good sound. 
(although it's not that simple, see bcast/docs/formats.html) 

The difference between a high quality jpeg (> 90% quality) and a raw picture 
seems more "academical" to me and can hardly be noticed at high frame rates. 
(and  BTW, I do very well notice the difference between 8bit and 16bit sound 
encoding ;-). At least at higher resolutions (PAL) the performance bottleneck 
is definitely the I/O to the hard disks (especially with my fscking VIA 
chipset, despite ATA-100, and 27MB/s throughput). 

But if you swear by raw grabs, and/or high quality jpeg encoding eats to much 
CPU time and raw RGB is faster, then grab RGBs and convert them to high 
quality jpegs (100%, if you want) with a script like:

#!/bin/bash
for i in *.ppm
 do
	convert $i -quality 99 jpg:`basename $i .ppm `.jpg
done

"convert" is part of the ImageMagick suite, just in the unlikely case you 
haven't heard of it. With "convert" you can even do some image processing 
along with the conversion (do a "man convert").

happy grabbing,
Amir C. Akhavan






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