When to resize in VirtualDub?

[GMaq]

Hi,
I've been converting a bunch of stuff from my old VCD collection to MPEG-4 using VirtualDub some Audio tools and YAMB, For the video I have been using XVid and DivX 6.2 with CQ 1 pass instead of 2-Pass and resizing up to 512x384 (4:3). On the VCD's where the original source was DVD I have been quite pleased with the results even on an HDTV. Some of the VCDs are from VHS and TV sources so I have been using MSU Deblocking filter .5 and MSU DeNoiser 1.6 and resizing to 512x384, Although I realize it is usually taboo to upsize from the source I feel it gives a better image on the TV and with CQ settings allows for more bitrate on the image, I have had mixed results partially due to the fact that you can't polish a turd, Poor source gives poor results, I am wondering if resizing should be done before the other filters or after the filters, Any suggestions are welcome. Thanks

[celtic_druid]

Before will be faster, deblocking would possibly work better after though. You might also want to look into using AVISynth together with XviDEncRaw. Encode directly to mp4 that way bypassing RGB24 colourspace conversions and VfW.

[guns1inger]

Most deblockers work best before resizing, simply because they expect certain block sizes based on common mpeg artifacts. Depending on how you resize, you can lose a lot of the effect if you deblock afterwards.

you can't polish a turd

According to Stanley Kubrick, you can if you freeze it.

[jagabo]

Before will be faster

Not if he's enlarging the frame (VCD to 512x384).

MSU deblocker (at least the regular one, not sure about the smart one) must be run at the original frame size. It needs the original 8x8 DCT block boundaries.

[celtic_druid]

Filtering after resizing means filtering more pixels, hence slower.

[jagabo]

Filtering after resizing means filtering more pixels, hence slower.

Sorry, I misinterpreted your original response. I thought by "Before will be faster" you meant resizing first would be faster -- because his original question was "I am wondering if resizing should be done before the other filters...?"

[GMaq]

Thanks for the responses,
In thinking it through, it would indeed make more sense to remove noise and artifacts then blow up the image, I just needed to hear it from someone else, but further to my first question is it better to denoise or deblock first ?? I find if you are tweaking the denoise enough to be noticeable it does more harm than good, people start looking like porcelain dolls! Is denoising worthwhile just for the increase in compression efficiency? Thanks Again.

[jagabo]

I find if you are tweaking the denoise enough to be noticeable it does more harm than good, people start looking like porcelain dolls!

I generally agree with that.

Is denoising worthwhile just for the increase in compression efficiency?

I think the issue similar to your first observation. To get substantial reduction in file size you'll have to filter so much you'll cause obvious damage to the picture.

A better is: why does resizing a VCD to 512x384 Xvid AVI file look better on your TV than just playing the original VCD? I have one player that has very obvious jaggies when playing VCD MPG files (it's obviously just displaying each scann line twice). Another that looks much smoother. A new player may be the better solution!

By the way, encoding with Xvid or Divx with a constant quantizer of 1 is pretty wasteful (and some set-top players won't be able to handle the high bitrates this can produce). Encoding with Q=2 is pretty much indistinguishable from Q=1 (even when looking at enlarged still frames) and results in much smaller files. Even Q=3 looks decent at normal playback speeds.

[GMaq]

jagabo,
Perhaps I typed the original post in a confusing way, What I meant is that I am using 1- pass Quality based or "CQ" depending on the Codec. I am using a Quantizer value of 3 in both cases because you are absolutely correct that any value lower than that would be ridiculous, the resultant MPEG-4 files are for use with an iPod and so far the bitrates have been in the acceptable limits, The original VCD's look just fine (relatively speaking) on my set top DVD player, Most of them contain Concert footage that I want to clip and mix into playlists on the iPod, I just want to preserve what's there with as little quality loss as possible. I do most other transcoding with Nero Recode or MPEG Streamclip but having more control with filters etc. I felt was worthwhile on some of the poorer quality footage. Judging by your observations about denoising it probably isn't worthwhile in most cases.

[SatStorm]

I use MSU Smart deblocking. This filter really eliminates the blocks: It's neccessary when you convert DVB grabbs to DVD.
You have to use this filter first in the chain. Before resizing, other filtering and all.

[GMaq]

SatStorm,
Do you use the "edge tuning" sliders in the MSU Smart DeBlocking filter and if so can you recommend some general settings ? Is the idea to get more edges to keep the image sharp, or do more edges mean stronger block corner artifacts?

[SatStorm]

I don't mess with the edge tuning settings. The default value works perfect for my DVB sources.
I use "directional filtering" only on extreme situations. This setting "cure" the macroblocks on very compressed (to the point of being unwatchable!) sources, but with a price to pay on all other parameters of the picture.

This filter is the reason I gonna upgrade soon my CPU. On my 2600XP, it takes too much time to encode when you enable it to the chain. It's time for a 5000 Athlon!

[GMaq]

SatStorm
Thanks for the suggestions on the DeBlocking filter There is only so much time for trial and error with this stuff, I will just leave it on the default settings, Obviously you are an AMD guy, I think this filter likes dual processors, I can do about 20fps with my 2.0ghz Intel Core Duo doing deblocking, resizing and DivX "Extreme Quality" encoding. I would imagine the latest AMD Dual Cores would be much faster yet!

[SatStorm]

@GMaq: Seems like you mess it a bit with the filters

There are 2 filters: MSU Smart Deblocking 0.5 (which takes ages to encode on my 2600XP) and MSU Deblocking 2.2 which takes a little bit more than your 2Ghz dual core (about 18 frames per second - Not bad for that old CPU...)