Help with motion artifacts in conversion

[Lester Burnham]

(I hope this doesn't breach conventions, I have posted it in the Xvid forum, too - I wasn't too sure which would be more appropriate - apologies if it's bad form).

Hi

I would be grateful for any advice with this.

I'm currently using Xvid codec for converting my DVD movies to play on my portable DivX / Xvid player (Archos AV440).

I'm currently using Auto GK to convert from DVD / VOB / mpg to Xvid AVI (mp3 audio - CBR 160kbps).

Auto GK is supposed to be pretty good at optimising the codec settings per input file, and does (typically) two-pass encoding, if using size based output files (it does one-pass encoding if selecting a quality percentage).

I've just had a slight problem converting the X Files movie (from my DVD copy). It's only really in the initial title sequence, where you have fluid (mercury-looking) that moves around a little, and that's become a little blocky with movement.

The output file was created to be around 1200Mb, and is currently showing a video bitrate of 1214kb/s.

Is it likely the reason I'm seeing the artifacts at this point because the bitrate must be a little on the low side for the movie to be converted without showing such effects?

Because I'm using Auto GK I don't have much else to play around with in terms of codec settings (as Auto GK controls all that), and I guess I'm mainly interested in whether - for the specifics of this film - I've made the output file too small?

Thanks for any help.

[bond]

do not cross post, striked for rule 8

http://forum.doom9.org/showthread.php?t=96535

[Teegedeck]

:logfile:

Reading your post in this thread (http://forum.doom9.org/showthread.php?t=95361) I wonder whether the reason might be that you overrode some AutoGK settings that are vital for AutoGK to do its job; like cropping or even resizing?

[Lester Burnham]

:logfile:



Sorry I don't have the logfile from this conversion any more - apologies, I know that doesn't exactly help, much.

BTW, I didn't mean to antagonise with my question in the Xvid forum, I merely thought as I was, or wanted to ask two questions, that were different - albeit perhaps subtly - that it wouldn't be a breach.

I was interested in a codec comment, and from here, a usability comment regarding Auto GK.



Reading your post in this thread (http://forum.doom9.org/showthread.php?t=95361) I wonder whether the reason might be that you overrode some AutoGK settings that are vital for AutoGK to do its job; like cropping or even resizing?



That was a conversion of a different movie, where I was finding the autocropping was removing more than I wanted. In that example (Fight Club, R1 DVD), there seemed to be some lack of clarity regarding the aspect ratio on the DVD - the case stated 2.40:1, whereas other regions and IMDB suggest that the reality was 2.35:1

The conversion that exhibits the blockies is the X-Files movie, and it's only really in the title sequence, with the fluid movement, really.

For this conversion, I did use a fixed width (640), used autocroping (although the threshold wasn't set to the default 34, I think it was set to 18. I didn't add any other cropping values, nor set any other options except for the credits stuff - but just for the end credits.

[Teegedeck]

Amorphous motion (like underwater-shots) in general poses a problem for block-based codecs. So it is well possible that you did nothing wrong but that simply the scene would need some boost of bitrate - provided that the rest of the encode really is free of blockiness. It could be interesting to see though what kind of resolution AutoGK would have proposed for the movie if you had not set it to 640x.

[Lester Burnham]

Amorphous motion (like underwater-shots) in general poses a problem for block-based codecs. So it is well possible that you did nothing wrong but that simply the scene would need some boost of bitrate - provided that the rest of the encode really is free of blockiness. It could be interesting to see though what kind of resolution AutoGK would have proposed for the movie if you had not set it to 640x.

I'll try that - what would you expect, given the symptoms?

I think I'll try and convert with increased output file size, and see what happens.

I haven't seen issues using DivX at similar output file sizes and the same input film.

I've also noticed (although it may only be on my portable player - I can't be sure if I've seen them when viewing on a PC) that my Xvid conversions can show smaller blocks in motion, or directly after pausing. In searches, I've found people describing, and showing captures of this effect, but in those cases, it was codec / decoding issues on their PC.

In my case, the only changes to playback, are likely to happen with firmware upgrades to my portable - which aren't that frequent. And again with the main problem, only seem to occur with Xvid encoded stuff.

[JimmyBarnes]

Hi

I would be grateful for any advice with this.

[snip]
I've just had a slight problem converting the X Files movie (from my DVD copy). It's only really in the initial title sequence, where you have fluid (mercury-looking) that moves around a little, and that's become a little blocky with movement.

The output file was created to be around 1200Mb, and is currently showing a video bitrate of 1214kb/s.

Is it likely the reason I'm seeing the artifacts at this point because the bitrate must be a little on the low side for the movie to be converted without showing such effects?

Because I'm using Auto GK I don't have much else to play around with in terms of codec settings (as Auto GK controls all that), and I guess I'm mainly interested in whether - for the specifics of this film - I've made the output file too small?

Thanks for any help.

Don't know anything about Auto GK, but when I first started encoding (to DivX, now all my encodes are XviD), I was very concerned re blockiness. To cut to the chase, the way I got rid of it was to make my encodes almost 80 % of the size of the encode using quantiser=2.00 at the same resolution (the usual figure quoted is 60%-75 %, depending on the movie, but I found results from that too variable). Since I used an 80 % target, blockiness is a non-issue (I use the utility Enc 1.0.3 to determine compressibility)

You didn't say anything about resolution - the important thing is bits/pixel, so if you increase the total size, you increase bpp, but another way to do it is to decrease resolution. Of course that leads to its own compromise in quality, but above 640x.. it's usually OK.

Hope this helps

JB