Dropped frames question

[perdomot]

I thought I had read that Divx has a low cpu utilization but when I capture with it, I lose more frames than I do with Huffyuv. Anybody know what gives?

[Nitemare]

What capture software are using? This may be a factor.

Also, and this is a guess mind you, I'd think that the level of compression achieved with Divx might be hard to do on the fly. That said, I've had no trouble using Divx to capture in virtualdub but I'm not trying 720x480 captures or anything THAT intensive.

If capturing from video, keep in mind that Divx does not support video interlacing.

[perdomot]

Hi,
I'm using VDub to capture 640 x 480. What do you mean it doesn't support interlacing? I'm converting vhs tapes to vcd so would this affect me?

[Gazorgan]

For most captures, anything over 288 vertical lines gets interlaced. So, to capture in DivX (BIG Mistake), you have to apply the de-interlace filter prior to converting to DivX.

Capture to MJPEG instead, then convert to VCD, if Huffyuv is taking up too much space. Don't bother with DivX, it only introduces compression errors. You may also try capturing directly to VCD resolution.

[Nitemare]

>>>Hi,
I'm using VDub to capture 640 x 480. What do you mean it doesn't support interlacing? I'm converting vhs tapes to vcd so would this affect me?>>>

Yes and no. If you make a de-interlaced capture you're fine. However, VHS home movies are ALWAYS interlaced. If in the U.S. (NTSC) anything over 240 lines is interlaced (288 for PAL...see above). If you select 352x240 in virtualdub as your capture resolution you should be good to go (NTSC vcd standard). Anything 240 lines or less is automatically de-interlaced in vdub. The divx codec should be fine for this.

If you wanted a higher quality SVCD from your VHS caps, then a MJPEG codec (which supports interlacing) and capture settings of 352x480 (2 interlaced fields of 240 lines each... again NTSC) will capture ALL of the video information available from your VHS tapes. Anything higher than this won't hurt, but is really a waste of system resources. With 352x480 you'll get all of the available video data.

Also, make sure you set sound for PCM, uncompressed capture and for home movies mono will be fine. It's possible that "unusual" sound capture settings can cause dropped frames. Any time I try ANYTHING other than PCM I seem to drop frames. This may not be true for everybody but I always have trouble.

Regards!
Nitemare

[SaSi]

It so happens that I was also capturing with VirtualDUB at a 720x576 resolution and was comparing DivX 5.02 with huffyuv. I was also having lost frames (not much, something like 2-3 per minute, nevertheless unacceptable).

I realized that I cannot capture and not lose frames, unless I select "Enable Directdraw acceleration" for both fields. Or disable preview, which I don't want. As soon as I enabled directdraw acceleration, utilization dropped from 80% or so to below 40% and no frames were lost.

DivX can be used to capture in 1 pass CBR mode and in 1 pass CQ mode. Always capture with max bitrate or max quality, of course, however constant quality will decrease utilization and help avoid dropped frames on slower machines because CQ will maintain a good quality without producing a 10Mbps stream (which taxes your disk I/O throughput and may cause dropped frames by itself).

Regarding the point that capturing with DivX is a mistake, I'd say it's a matter of what bad experiences each one has. DivX DOES introduce a small loss in quality, even in max quality, however for VHS content, this, in my humble opinion, is beneficial as the small blur helps eliminate some of the noise in the VHS tape.

Also, it's a matter of whether one has 20 Gb / hour (for huffyuv) to spare or 1 Gb/per hour (for DivX).

[perdomot]

Well, I tested the Enable Directdraw and didn't drop frames although cpu use remained high. I'll test it out more fully later. Since I am converting to a 352 x 240 resolution, should I capture at that resolution or continue capturing at 640 x 480? I am making XVCDs where I alter the bitrate depending on the length of the movie so I thought capturing at a higher resolution would be handy when I compress it down to mpegs. What should I do?

[Nitemare]

Opinions vary on this but I'd say capture at 352x240. The less your MPG encoder has to manipulate (i.e. resize) the capture the better. You'll get less dropped frames and be deinterlaced automatically (in virtualdub). You can still use directdraw acceleration but use it only on 1 field, probably A. If you try it and it has jerky movement, use field B instead.

Capturing VHS any wider than 352 is always a waste. This is fact. VHS resolution is 352x480. Unless you need it wider for other reasons (making a DVD and have no clue how to do it with anything other than a 720x480 file) then capturing it wider than 352 causes both your capture card and eventually your MPEG encoder to resize it, especially if you're making a video cd at 352x240.

I don't want to start a war here and I'm certain that others have made many excellent captures at higher resolutions, but quality is in the eye of the beholder. What they call "clearer and sharper" I call "well placed artifacting". 352x480 matches the signal on the VHS. If you deinterlace this signal you end up with 352x240 anyway so you might as well capture at that and save the deinterlacing step.

This will save you and your PC a lot of processing time. If you cap at 640x480 you must capture, deinterlace, resize, make your MPG (which has lost quality during the resizing and deinterlacing) , and burn. If you cap at 352x240 you just capture, make MPG and burn. No resizing or deinterlacing is needed and you might see a noticeable quality improvement.

As always, the best bet is to grab some cd-rws and run your own tests. I do what I do for a reason, others do what they do for a reason. We may disagree about what's best but we all know what's best for US. (Still trying to avoid a war!!) We can all "advise" you, but you're the one who's got to live with discs you make. Try it as many ways as you need to to make you happy with the end results.

For what it's worth, most of us are always trying to improve our capture quality and methods. My advice this month may be different than my advice six months from now. Keep that in mind and good luck!!
Nitemare

[perdomot]

Hi Nitemare,
I compared two mpegs, one captured at 640x480 and one at 352x240, and there were big differences between the two. Most noticably, there were considerably less artifacts in the 640 capture and the amount of detail in lines was much smoother. You were right that it does take less time when you capture at 352x240 but the loss of quality is too much. I use Avisynth to do an IVTC and smoothing before I encode to mpeg and that basically doubles the time. If I use the Noise Reduction filter in TMPEG, an hour and 40 minute movie takes around 12 hours but it makes the mpeg look even better. I'm not sure if you've compared the two but from what I saw, there was a big difference in image quality. Try capturing an avi file at the two resolutions, encode them and compare. Here's the script I use to clean up the mpeg:

LoadPlugin("D:\Documents\Vid Tools\decomb405legacy\DecombLegacy.dll")
LoadPlugin("D:\Documents\Vid Tools\PeachSmoother\PeachSmoother.dll")
AVISource("J:\VCR capture\capture.avi")
TELECIDE(GUIDE=1,SHOW=FALSE)
DECIMATE(CYCLE=5,SHOW=FALSE)
PeachSmoother(NoiseReduction = 60, Stability = 25, Spatial = 140)

Just change the plugin and avisource info and give it a try. I think you'll be able to see the difference. I could. Thanks for your input.

[Nitemare]

Hi Perdomot,

Just for fun try the same capture at 352x480 and see if there is a huge quality difference than in the 640x480 file. My whole point was that the 352 width will capture ALL of the video data on the VHS. A 240 line capture loses half of your video data while the 480 line capture keeps this data but then has to be "handled" to make it palatable to your PC (and the VCD standard)

I make SVCDs from MJPEG AVIs, the SVCD standard is 480x480 so I can keep all of my video data without IVTC or de-interlace. Just capture, make file, burn file, enjoy! To my eyes my SVCDs are are identical to my VHS tapes (in my DVD player on the TV) without the need for any extra processing. Yes, they look like crap on the PC, but I'm not watching them there.

When I want to make a PC watchable file, I have to de-interlace, etc. etc. If I blend the fields this causes my video files to "pulse" as the interlacing is "corrected". My other choice is to eliminate one of the fields. Now I have no pulsing but I've lost half of my video data and it has some "jaggies". Yes, noise reduction can help the "pulsing" but not eliminate it, and I can SEE the degraded quality caused by the noise reduction. Can't stand it. In that instance, 352x240 is my answer.

Again, these are my preferences. I don't make VCDs any more so my input is probably irrelevant... but seriously... humor me and try the 352x480 capture. You might be surprised... then again, maybe you won't. It's always according to your own preference. My preference is to keep my MPG encoding fast and easy. If you've got the time and can actually improve you VHS signal, go for it!

[perdomot]

Hi Nitemare,
Actually, that was the first resolution I tried but the avi and the mpeg had a long, stretched look as if someone had grab the top and bottom of the screen and pulled. It looked weird.
I make XVCDs since my dvd player doesn't do SVCD and the higher bitrates make my XVCDs look just as good as my vhs tapes. I used to capture at 352x240 and it was a lot faster. An hour long clip would take only 45 minutes but the difference in quality is so noticible. I'm probably going to limit my use of the noise reduction filter since that is what takes the most time but I think I'll stick with this method for now. Thanks.

[SaSi]

If I guess right, you are encoding with Tmpgenc and using it's noise reduction filter. It does tend to multiply encoding time by a factor of 2 ~ 3, unfortunatelly.

Don't use any Tmpgenc filters. While they are excellent they take too much time. Adding 2 or three filters can make a single pass encoding to take more than 30 hours on a P4/2.67 That's not acceptable.

If you are making a VCD at 352 x 288 then capture at that resolution. Your end result will be better. The movie I was capturing last night (when answering your question) was a comercially produced VHS version of Star Trek 1: The Movie. A trekkie friend asked me to capture it and convert it to DVD, and while at it, apply "those magical digital filters to improve the quality".

What I've seen is that VHS is totaly a waste to go to DVD resolution. Although you can capture VHS at 720x576, the VHS tape doesn't have that much resolution in it. Several older VHS players will only produce 240 lines. Newest, top level ones will make 480. I am guessing that capturing at higher resolutions causes the capture engine to "invent" scan lines and perhaps that is the reason for that increased CPU utilisation that both you and myself saw.

I also made a test and captured from an 8mm camcorder at 720x576. Picture clarity was much higher and CPU utilisation was low. What do you make of it?

[perdomot]

Hi Sasi,
The TMPEG filter takes a very long time. If I just encode using Avisynth to clean up the avi a bit, it takes about twice as long as the video's lenth. I think I'll save any filter work for my 12 hour work days since all I have to do is set it and let it encode. I used to capture at 352x240 and encode but I compared the results with a 640x480 capture and the larger capture produced a much better mpeg. By that I mean less artifacts. I also make XVCDs with a higher bit rate which also improves image quality. You are right that encoding to DVD quality resolution is pointless for vhs tape conversions but right now I'm only working on tapes to archive my collection before a vcr chews it up. After that, I intend to get a DVD burner for future use but right now, XVCD is the way to go

[Nitemare]

perdomot,

Hello again! Yes, capturing at 352x480 does give the avi a wierd and stretched look. This is completely normal. When you load this file into your MPEG encoder as 4:3 source, the MPEG encoder displays and processes it correctly. Even if it doesn't, your TV will display it correctly.

I understand why you'd want it to LOOK 4:3 while processing and that's perfectly okay. For that, 640x480 would be the correct resolution. If you're happy with the captures and you're no longer dropping frames then it sounds as though you've figured out your problem.

Congratulations!
Nitemare

[perdomot]

Hmmm,
Let me try this again. I think I was using the 1:1 setting. I'll let you know. Thanks.

[perdomot]

Well, it seems to work. The mpeg looks good and even with the noise reduction on, it cut down the encoding time by nearly half. I was able to capture using Divx and didn't drop any frames. Thanks for the help.