OT- VCD seems superior to SVCD, what gives?

markrad wrote on 12/3/2002, 1:49 AM
I rendered a one minute avi file to both VCD and SVCD NTSC formats on CD-R. The SVCD was twice as large (no surprise there). Although the SVCD did appear brighter and with somewhat better color, it exhibited bands of horizontal artifact when the camera panned the subject. The artifact did not show up when viewing the VCD project. Both projects were created using VCDEasy and played back on my Apex 1100W DVD player. Any ideas on what I could be overlooking? With the increased bitrate of SVCD this is opposite of what I would have expected. If you need more details just ask.
MR

Comments

riredale wrote on 12/3/2002, 11:15 AM
I have very little expertise in VCD and SVCD, but I recall that VCD uses MPEG1 and SVCD uses MPEG2. MPEG1 ignores field interlacing issues since the resolution is so low it deals with just one field of the video frame. MPEG2, however, works with both fields. You mentioned horizontal artifacts. Do they look like a hair comb? If so, then perhaps you have the fields reversed. In every MPEG2 codec there is a checkbox to the effect of "Upper field first" or "Lower field first." Try encoding with the alternate setting and see how it looks.
SonyDennis wrote on 12/3/2002, 2:46 PM
I agree with Riredale, these are probably interlace artifacts. If you're seeing them on an interlaced monitor, something is wrong. Please check your source footage 'media properties' to make sure Field Order is set correctly. If it's not set right, Vegas will not deinterlace before scaling, which can cause moire patterns that appear as a break-up during horizontal motion.
///d@
owlsroost wrote on 12/3/2002, 3:05 PM
For encoding to SVCD, see http://www.sonicfoundry.com/forums/ShowMessage.asp?MessageID=110318&Replies=6&Page=2 and http://www.sonicfoundry.com/forums/ShowMessage.asp?ForumID=4&MessageID=106772

The main issue is that the "stretch video to fill output frame size" box needs to be ticked in the 'Render As' dialogue.

Since this issue keeps coming up with SVCD output, could SF please explain why it goes wrong if the above box is not ticked (even if the field order of the source clips, the project, and the encoding template are all the same, and the render quality is set to 'best').

Or does the reply from SonicDennis imply that VV3 can't correctly do vertical re-sizing of interlaced video, since it suggests that it has to de-interlace it before scaling - which it shouldn't need to do.

Tony
markrad wrote on 12/4/2002, 2:01 AM
Owlsroost,
Thanks for sharing your experience with SVCD.
Some people suggeseted field order. I tried SWITCHING the field order to UPPER field first and it actually made things more jerky. I was pretty confident with the field order to begin with because everything lined up, source file, project, render etc.

I tried your suggestions and will share my results:

<The main change is in the 'Render As' dialog - tick the box 'Stretch video to fill output frame size (do not letterbox)'.> This was the single BIGGEST improvement.

<The other change is on the custom MPEG settings -> Advanced Video page - tick the 'Write sequence display extension' box (this seems to be an oversight in the supplied template - the MPEG encoding guide says it should be ticked)> Not sure where the "MPEG encoding guide" is but I tried this at the same time I chose the Stretch video function.

<Also found that CBR encoding seems to give better quality than VBR (but then this is not unusual...).> In my case when I tried CBR (constant bit rate)I could not detect any appreciable difference but I'm thinking results would vary based on the project at hand.

Do I need to be concerned with the pixel aspect ratio in the properties section or will rendering using the SVCD template take care of that??

Thanks to everyone who replied.
MR
owlsroost wrote on 12/4/2002, 7:48 AM
> Not sure where the "MPEG encoding guide" is

Download it from http://www.sonicfoundry.com/download/step2.asp?DID=363

> In my case when I tried CBR (constant bit rate)I could not detect any appreciable difference but I'm thinking results would vary based on the project at hand.

Yes, agreed. VBR encoding is mainly about keeping the file size to a minimum while maximising the quality - this works well for DVD where the average might be 5 - 6 Mb/s, peaking to 9 Mb/s, but standard compliant SVCD only allows up to about 2.4 - 2.5 Mb/s peak, so you don't really have much headroom to play with above an average bitrate of 2 Mb/s (and you wouldn't want to drop much below this average if quality is important).

> Do I need to be concerned with the pixel aspect ratio in the properties section or will rendering using the SVCD template take care of that??

No, leave that set in project properties as you would normally for your source material. The SVCD template handles the necessary re-sizing etc.

Tony