Your experience with Two-Pass Rendering?

[Norm Sanders]

Anyone else use two-pass when rendering their MPEG2 files? I've always used it because the help section says that it MAY increase the quality of the file ... even though it takes about 2x as long to render.

However, when rendering a WMV file yesterday, I took it off the default CBR and chose CBR-Two Pass thinking the quality may look better ... after I rendered it, I watched it and it actually looked (to me) lower quality than the standard render and had more artifacts in the video.

What gives?

What are your experiences, and DOES Two-Pass really give better quality in the video image? Am I wasting my time when doing it for MPEG2 files? Anytime it's a bad idea based on certain plug-in's/FX/Motion Blur?

 

[kplo]

You might want to try 2 pass VBR rendering. This allows the program to analyze the file on the first pass and then vary the bit rate as necessary. This works very well in TMPGENC (I use Vegas 4.0e which doesn't have 2 pass).
Hope this helps.
Ken

 

[Norm Sanders]

What's TMPGENC? I think I did look at 2 Pass VBR (assuming your talking about WMV files), but it had even more options under that ... not know what to pick or why, I left it alone.

 

[SafetyO]

What's TMPGENC? I think I did look at 2 Pass VBR (assuming your talking about WMV files), but it had even more options under that ... not know what to pick or why, I left it alone.

wow...do a google search on "TMPGENC". All the info you could want. FWIW, I've had pretty good results for some TMPGENC renders, not so good with others. I mostly stick to what's in Vegas 6 now.

 

[kplo]

If you're using Vegas 6, I believe it includes 2 pass VBR as an option when encoding to MPEG2 streams. I'd use that setting.
I've just been a bit reluctant to upgrade to V6 because of some of the posts reporting problems with it. Also, my 3 year old system (P4 1.8gz) is probably underpowered for it.
Ken

 

[Norm Sanders]

I'd check the min sys. req., as I'm pretty sure you can run 6 just as well. As far as bugs, most have been worked out with the latest release, and I'm working fine with it.

Okay, so I found the site for TMPGENC at http://www.tmpg-inc.com ... is this supposed to be better than MPEG2? I'll check it out further, but I guess "if it ain't broke, don't fix it" applies here ... I've never had a problem with my MPEG2 files from Vegas.

When I asked what TMPGENC was, I was thinking it was initials for something like FWIW, IMHO, etc. Thanks for the clarification.

 

[SafetyO]

When I asked what TMPGENC was, I was thinking it was initials for something like FWIW, IMHO, etc. Thanks for the clarification.

TMPGEnc came from Tsunami MPEGEncoder.

 

[mcsmooth]

Okay, so I found the site for TMPGENC at http://www.tmpg-inc.com ... is this supposed to be better than MPEG2? I'll check it out further, but I guess "if it ain't broke, don't fix it" applies here ... I've never had a problem with my MPEG2 files from Vegas.

TMPGENC is the name of the program, it does mpeg2 encoding. So it doesn't really make sense to ask if it is better than mpeg2, it does mpeg2. The question is, does it encode mpeg2 better than vegas? Anydbody know this? I'm a bit new to Vegas and haven't bothered trying the mpeg2 encoding, but am very familiar with tmpgenc (2.5).

I've been using this encoder for several years (I was never satisfied with any NLE's or DVD authoring program's built in encoding) and still encode all my mpeg1 and mpeg2 (VBR) with it. It used to have the best mpeg1 compression, but hard to say if it is the best for mpeg2. It is extremely capable and has so many options for fine tuning. Unfortunately this makes it even more difficult to chose options. When you select a DVD output template it greys out options that might make your steam non dvd compliant, so that helps. Then, after you do testing and find a setting you like, you may never need to change options again. A downside to this programs mpeg2 compression is that it is fairly slow compared to others out there, but often it is worth the wait.

 

[Norm Sanders]

Perhaps if I did an apples to apples comparison I'd see a difference between Vegas' MPEG2 render, and TMPGENC's, but otherwise I've always been very happy with the Vegas result (again, always using two-pass) ... hopefully one of the Mods' or anyone else who's familiar with both programs can speak from experience on the difference in quality, if any.

It does sound like, however, that there would be an extra step to use the TMPGENC to render, as I'm pretty sure I'd have to render out to an AVI first, THEN import into TMPGENC to render MPEG2 vs. right now I can go direct from Vegas. Also, I'm not sure how I'd handle my 5.1 surround sounds, as I don't know how to export those from Vegas other than to ac3 files.

 

[mcsmooth]

I checked out Vegas' options for mpeg2 and it seems to cover most everything you'd ever need and quality seems like it would be good enough for most applications. Obviously its great for 24p since it was designed to handle this for you. And yes, the extra step of an external encoder does mean an extra render if DVD is your only output. I typically render a DV version of everything, so it doesn't matter (however, you can potentially lose a little quality in that step due to DV re-encoding of any edited frames). I do a lot of short edits, so its easy for me to batch encode a bunch of them with tmpgenc while I'm sleeping/at work. From what I've seen, I'll probably just use Vegas for anything I just need straight to DVD. Then prized work, I'd probably go to a uncompressed format (with possability of external fx) and use an external encoder.

For your original question, I'd say it is true that 2-pass MAY be better, and if time permits, it is always the best route. It is more likely to do a better job optimizing the bandwidth for the parts of the video that are "variable" like fast motion which requires higher bitrates and still motion that can drop the bandwidth. With one pass, the encoder has no way of knowing what is to come in the next few frames. As with most encoding, the type of video that is the source has a lot to do with what method will work best (ie, news broadcast vs sports), so different settings work better with different sources.