Aspect ratio question

[Flying dutchman]

I am about to start a larger SVCD project. Now that Avi_io can capture in custom sizes, and my PC is fast enough to produce 480x576 Huffy files, I am tempted to capture in this resolution and save a lot of rendering/ scaling time and maybe gain some quality because MJPG encoding becomes unnecessary. I would use Premiere 5.1 for NLE and tMpegenc or bbMpeg for rendering to SVCD.

My questions:

- The SVCD resolution has an awkward aspect ratio on the PC screen. If I render titles in Premiere, will they have the correct 4:3 aspect ratio upon playback?

- If I would capture in full-resolution MJPG and leave the scaling to Premiere, will it scale as good as VirtualDub?

[Dr Mordrid]

You have two choices: capture & edit at full frame then render it to MPEG at 480x576 or capture at 480x576 and render to MPEG without scaling.

Adding text/graphics doesn't cause any aspect ratio issues that can't be corrected on the timeline with the Motion settings. Actually, there shouldn't be any.

Capturing at 480x576 gives faster rendering times because there is no scaling done during the MPEG encoding. Capturing at full frame gives better quality because it feeds the encoders quantizer a greater variety of values. This can help prevent block artifacts with some sources.

Uppance: IF the 480x576 source is clean (ex: few shadows & dark color regions/few large solid color regions) then go for 480x576. Otherwise go for full frame.

For best quality output with any source size/type I'd suggest frameserving TMPGEnc 12a direct from Premiere's timeline using AVISynth. If you need the software and docs on how to do this mail me. I have a kit already assembled with an updated version of AVISynth (over and above what's on Bens website).

Dr. Mordrid


[This message has been edited by Dr Mordrid (edited 26 June 2001).]

[Flying dutchman]

Hi Doc,

I am tempted to go for 480x576 YUY2 for several reasons. I asked Markus Zingg how the "custom frame size" in AVI_IO works, and he told me the program simply inquires if the capture driver supports this particular format directly and if yes, enables it. So it's NOT some kind of scaling performed by AVI_IO.

I am currently experimenting with different scaling methods. I have a test DVD that contains a high-resolution test picture at 720x576. I just want to find out how I can get the best resolution at 480 pixels wide, and if scaling down from a higher resolution gives a better or worse resolution.
Also I'd very much like to know how much the MJPG compression would contribute to degradation of the picture. I'll keep you informed.

BTW, I have no problems frameserving from Premiere. Do you have a newer version of Avisynth than the one on Ben's page?

[Dr Mordrid]

Low to medium bitrate MJPeg (up to 3 mb/s) will show DCT recompresson artifacts in effects, titles etc.

High bitrate MJPeg (5 mb/s and up) will show little degradation. What little it does show will be in regions with high contrast (color or lumance).

10 mb/s MJPeg and up is essentially lossless.

I do have a newer version of AVISynth. Bens latest build was 1.0 build 3. I'm now using Avisynth 1.0 beta build 31 + Premiere plugin 0.28beta build 36.

Another group has been adding features and updating the code for it and other OpenSource programs. Look here:

http://www.videotools.net

Dr. Mordrid


[This message has been edited by Dr Mordrid (edited 27 June 2001).]