how do you create halfsize videofiles?

[fiepke]

Hi,

I'm trying to create a backup of a dvd and want to reencode an extra to half-size (I don't know the technical term for fullsize/halfsize, seen it in a thread once...but can't find it anymore). What I mean by this is that I want to change the resolution from 720x576 to 352x288. First I created a .d2v file with dvd2avi and then created a .avs with the following in it:

LoadPlugin("C:\Program Files\MPEG2Dec\mpeg2dec.dll")
mpeg2source("D:\DVD\extra06.d2v")
BilinearResize(352,288)
ResampleAudio(44100)

I added the file in CCE and did a one-pass vbr first, followed by a dual-pass vbr. The result was a movie with a resulution of 720x576 but the moving part was 352x288. Or in other words, a 352x288 movie with extremely large black borders making it 720x576. I also tried changing the mpeg2 settings in CCE by selecting the 'half horizontal resolution' and 'half vertical resolution' but the results were the same.

It didn't seem right to me to have my results, maybe someone can help me out? Do I need to crop the image as well after the BilinearResize? According to the avisynth website 'The BilinearResize filter rescales the input video frames to an arbitrary new resolution.' So cropping shouldn't be necessary... I'm kinda confused as to what to do to end up with a smaller endresult.

Thanx!

PS : If someone remembers the thread where someone explained the various compliant video resolutions for a dvd, please let me know, I've been searching for 3 hours and can't find it...

Fiepke

Added:

Dammit, this happens every time I post...I find a possible solution five minutes later! After more searching in the forum I came across this thread:

http://forum.doom9.org/showthread.php?s=&threadid=23195

Will check that out first.

[fiepke]

As can be read in the thread I pasted above, the solution lies in deselecting 'dvd compliant' in cce. The result will be a movie which is resized according to your avisynth settings in the .avs file.

The results however were different then I had hoped. I thought if I created a half-D1 movie, the size would be considerably smaller. I did a one pass first on 0 Kbit min, 9500 Kbit max. Followed by a 2-pass encoding of the same file at 2400 avg, 0 min, 9500 max. The result was barely 10% smaller than encoding it a full-D1. When I think about it, the amount of pixels shouldn't make the difference, since my average bitrate is still 2400. Even if there were only 8 pixels to be encoded, the result will probably be the same (size).

However, changing the average bitrate to half of the bitrate used at Full-D1 didn't work either, the size was down but so was the quality. Changing it to 1200 was not a beautifull sight :)

Maybe half D1 was never meant to be used for downsizing a full-D1 movie, but rather for backward compatibility with VCD.

Greetz,

fiepke

[ronnylov]

Half D1 (PAL) is not 352x288 it is 352x576 and that's not compatible with VCD. You can use 352x288 as MPEG1 on a DVD which is VCD compatible if you change the audio sampling frequency (48 kHz on DVD, 44.1 kHz on VCD).

When you decrease the resolution then the artifacts will be larger. With the full resolution encoding you won't see the artifacts on the TV as easily as the half resolution artifacts. In the thread you linked to somebody said that 2/3 of the bitrate was needed when transcoding to half resolution. That sounds reasonable. The 6000 kbit/s CBR at full D1 should look OK at 4000 kbit/s CBR at half D1 (352x576).

[fiepke]

Ah thanks for the information.

[auenf]

you can use 352x288 in mpeg-1 or mpeg-2 in dvd.

Enf...

[ronnylov]

"you can use 352x288 in mpeg-1 or mpeg-2 in dvd"

Yes, but it's not according to the DVD-standards. SpruceUp does not complain but my standalone DVD-player can only play this resolution in MPEG-1 mode. It does not work in MPEG-2... It may work in many playes but it is still not a valid DVD-resolution in MPEG-2.

Here's a quote from DVD-demystified (http://www.dvddemystified.com/dvdfaq.html#3.4):
Allowable picture resolutions are:
MPEG-2, 525/60 (NTSC): 720x480, 704x480, 352x480
MPEG-2, 625/50 (PAL): 720x576, 704x576, 352x576
MPEG-1, 525/60 (NTSC): 352x240
MPEG-1, 625/50 (PAL): 352x288

and MPEG-1 video rate is limited to 1.856 Mbps with a typical rate of 1.15 Mbps