Trying to encode DVD to DIVX/AVI or h264

[cassavetes]

hi.

I'm trying to encode some of my dvds to avi for traveling lighter. but I seem to run into problems in terms of image quality. I've seen a lot of TV Rips out there that have a filesize of around 350mb for 45min. episodes that look nearly as good as a dvd. I never acquire such quality whatever I do. I tried to scale my files to as low as 512x... but loose image quality of course. I have one of those tv-ep files opened in quicktime and hit apple+i for information and it tells me it is 640x352 and has a data rate of 1151 kBit/s. if I was to select those stats for my encoding in ffmpegx it would result in a much larger file or less quality (or both...).

what I usually do is:
1) make a one file vob of my dvd.
2) load it into ffmpegx.
3) choose avi/divx (mpeg4,mencoder).
4) autocrop the file and preview
5) choose aspect ratio (most of the time that's 1.85:1 and scale it down from 720x... to something around 640x...)
6) click on best for bitrate calculation which most of the time results in something around 1000kbit/s
7) choose deinterlace (if needed)
8) choose high quality, b-frames, all the other stuff in that options tab.
9) three pass encoding (when the window comes up after the first pass, I leave it at the bitrate I chose in the beginning)
10) for scaling I usually choose lanczos
11) I leave all the other stuff untouched.

still my video looks far from as good as stuff I have seen on the net. what am I doing wrong. where is that hidden feature I don't know about??

please help me and point out my stupidity...

thanks a lot
cas

[tomlee59]

For conversion into DivX/XviD, I use D-Vision3. Its default choices produce very good output (and you can override the defaults if you want/need to). I recommend giving that app a try.

Also, lanczos can produce problems of its own (aside from slow encoding). Precisely because of its frequency response, any Gibbs phenomenon-related artifacts introduced by the rest of the encoding process can result in visually objectionable results. If your quality issues have more to do with a "graininess" or coarseness, as opposed to motion artifacts or blur, you may wish to reconsider your choice of scaling algorithm.

[cassavetes]

thanks for your help. I've tried d-vision before moving to ffmpegx in hope of a higher tweakability which I'm obviously not quite the master of.
graininess is not the problem. artifacts and especially bluriness seem to be a better description to what I see. what would I change to avoid that?
and what can I achieve by tweaking the qmin qmax amounts?

[dr9553]

I have often wondered this myself. Any insight would be great....

The only thing that stand out in my mind is to check your audio encoding settings then you can manually adjust your video bitrate to maximize that.

I have also read about people using more than 2 passes to make their avis or eve mpeg-2 videos... i thought that anything over 2 was kind of a waste...

[tomlee59]

If you are noticing objectionable blur on static images, then your resolution is too low. If the blurring is mainly observed when things are moving, then that's a motion artifact problem. Fixing either will result in a higher bitrate.

As for your qmin/qmax question, these parameters are essentially used as acceptance criteria by the encoder to meet the user-specified target bitrate. A higher number implies that you are willing to accept larger quantization errors (lower quality). If you choose quantizer values that are too tight (low), then the encoder may not meet the target bitrate, and the file size can end up larger than expected. But choosing the numbers too high can result in sloppy encoding decisions, with a corresponding loss in quality.

In your case, the blurriness you're observing suggests that you should jack up the resolutions until you see what you like on static images. Then you can experiment with bitrate (either directly, or through adjustment of qmin/qmax) until you achieve a balance between filesize and motion artifacts. Multiple-pass encoding will improve the quality/filesize ratio, but the gains beyond two passes are unlikely to make the longer encode times worthwhile (IMNHO).

Also, it may help to select a target framerate of 24fps (if you aren't already doing so). That reduces the bitrate needed for a given quality. You may also wish to re-examine the clips that you've downloaded; resolution is certainly important, but so is framerate. Perhaps the clips you've identified as looking better than the ones you encode are not full TV-framerate?

Finally, make sure that you're comparing apples to apples. Does your output look significantly inferior to the source that created it? Or are you comparing two different clips altogether? Needless to say, material that starts off as, say, HD, may produce different results (for the same bitrate) as material encoded from DVD. I just don't want you to waste a lot of time chasing a phantom.

[And do make sure that you're not burning too much bitrate on the audio track; save it for the vid]

[cassavetes]

thank you for your thorough post.
still trying to make my way through it.
let me just ask really specific as you seem to really know your way around these kind of things.
if you had a vob file of a movie say 90min. dvd aspectratio of 720x576. what size bitrates and option/filters would you suggest to make this look good in say 700mb?
and about the audio. I never changed that. it is usually set to mp3, 128kbits, 48khz, stereo, cbr. isn't that okay?
best. thanks for all your help!
cas

[tomlee59]

The audio specs are fine, so you can leave those as they are.

A 90 minute movie will fit nicely on a single CDR with good quality (of course, "quality" is highly subjective). I do this all the time with D-Vision, letting it choose the resolutions for me. In your case, you're starting with a PAL DVD, so no need or desire to change the framerate. Just tell D-Vision to fit it on a single 700MB CDR, and let it choose the rest for you. In this case, it'll select something close to 1Mbit/sec for the video rate.

If the output doesn't look good to you, post back with more specifics. And if you could point out a site that has an example of output that does look good to you, post the URL so that someone here can see what, if anything, is different about it.

[cassavetes]

well I did two movies in d-vision. both around 90min. one is in black and white which looks okay (the b&w being a problem for any digital medium I think) and is around 680mb. fine by me.
the other is in colour and looks great. although pretty grainy. but the file size I'm wondering about that because I used the exact same preferences as for the first movie but this one turned out to be 1.83gb. strange...

[cassavetes]

and again. a longer movie. about 2:30h. I tried to make it 1.4gb (or 2cd-r) but it turns out to be way larger than that. why is that? any ideas? thx

[tomlee59]

Well, since I don't have a webcam looking over your shoulder, you'll have to give more information than "why doesn't it do what I want?"

Tell us WHAT YOU DID, then maybe we can figure out what you did wrong.

We want to help, but give us something to work with!

[cassavetes]

Sorry bout that.
Here's what I did.
1. I openend the desired Video_TS Folder from my hard disk (it got there via MTR) in D-Vision.
2. It loaded fine. Chose the Main Feature automatically.
3. I didn't change anything in the "general" tab
4. In "Video" tab I chose deinterlace (video is interlaced as seen by checking vobs in vlc). noise reduction and sharpness (set to medium). Codec is Xvid, 2-pass, best/slow. Final Size set to 1000mb (video is 2h20min long, 700mb is a bit low I think) and video bitrate left alone as that is supposed to be done by setting the filesize: it set it to 854kbits/s).
5. Dimensions are automatically rendered to 576x320 16:9.
6. Crop I left alone.
7. Set the Videoframerate to be changed from 29.97 to 25fps.
8. In Audio Tab I set Codec to MP3, Complete Encoding, 128kbit, Stereo, Constant, Gain 3.
9. Subtitles I left alone.
10. Create Task.

That's what I did. But the file got way bigger than the desired 1gb. More around 2,4gb. Let me know what else you need to know.

Thx for your patience!

[cassavetes]

and another thing:
I tried to encode a one file vob with ffmpegx's ipod 640x codec. the quality is fine (although it takes quite long) but the resulting video turns black after about half the playback. the sound is still there but the picture is gone black. I thought this might be a result of the one file vob which mpeg streamclip tells me has timecode errors. I repaired those and saved as a new .vob file (although the timecode repair doesn't seem to be saved with it as the new file still had the same errors). do you know anything about that?
sorry to bother you with all those questions. I'm just trying to figure that out for once.
thx for your help.
best
cas