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Glitches in output rendered MPEG2 files

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Giles Meehan
Glitches in output rendered MPEG2 files
on Apr 5, 2014 at 8:01:42 am

Hello! I have used Vegas Pro for several years, and had this problem for a long time, but on my current project, it's being a nightmare!

I'm currently on version 12.0 build 394, but it's happened on previous versions.

When I render to a DVD Architect MPEG2 video file, I sometimes get "glitches" - moments where the image freezes or nearly freezes for about 2 frames, and then catches up again. I have several on my current 1-hour video.

The glitches often appear to happen within about a second of a cross-fade or similar, but not always. They usually happen in the same places, but sometimes tweaking the render settings makes some disappear and others appear.

The current project is a mixture of Sony AVCHD 50i, HDV 50i and DV-AVI PAL.

There were slightly fewer of these glitches when I used 2-pass VBR, and when I reduced (surprisingly?) average bitrate back to 6.0 Mbps (from 8.0), and reduced maximum bitrate to 7.0 Mbps, but several of them are still there. GPU rendering is off, and I have switched "Number of render threads" down from 16 to 1, which I'm not sure if it made any difference at all?

It was also slightly better when I rendered the whole project as DV-AVI PAL (with no glitches), and then rendered that to MPEG2, but even that had a few glitches in, and apparent resolution was worse as well.

Has anyone got any ideas at all, please? I cannot believe that a professional editing program can't produce a usable DVD?! Thank you


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Graham Bernard
Re: Glitches in output rendered MPEG2 files
on Apr 5, 2014 at 8:21:43 am

2 points:

1/- Your Build is very early. The latest is B770. This may not be an issue but worthy of consideration by you.

2/- I'd be putting your file through BITRARE Viewer. This may well identify a SPIKE in the Bitrate that us making your output judder. I've had this and used BRV to identify.

Cheers

Grazie

Video Content Creator and Potter
PC 7 64-bit 16gb * Intel® Core™i7-2600k Quad Core 3.40GHz * 2GB NVIDIA GEFORCE GTX 560 Ti
Cameras: Canon XF300 + PowerShot SX50HS Bridge


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John Rofrano
Re: Glitches in output rendered MPEG2 files
on Apr 5, 2014 at 11:23:00 am

I agree with Graham. There are a lot of fixes between build 394 and 770. If you're having problems and you're not at the latest level of the software, the first step is to get up to the current level and see if it has been fixed.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Steve Rhoden
Re: Glitches in output rendered MPEG2 files
on Apr 5, 2014 at 12:50:08 pm

What are you playing them back in when you notice these glitches?

Steve Rhoden
(Cow Leader)
Film Editor & Compositor.
Filmex Creative Media.
http://www.facebook.com/FilmexCreativeMedia
1-876-461-9019


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Giles Meehan
Re: Glitches in output rendered MPEG2 files
on Apr 5, 2014 at 4:53:27 pm

Thank you all very much. I hadn't realised that I hadn't updated it for so long, I'll do that next. But, I've had the same problem in previous versions of Vegas Pro (10 and 11).

I get these glitches playing back in Windows Media Player on the PC, but they also show up on the finished DVD...

Wow! I've just realised for the first time - that I don't think the glitches show up when I put the MPEG file back onto the Vegas timeline. I need to check that again, but that would show there's no problem with the rendered file, but just with playback.

I'll try all of that and the bitrate viewer, and report back, and might then need to ask how to iron out any spikes if possible.

Thank you again! Giles.


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Giles Meehan
Re: Glitches in output rendered MPEG2 files
on Apr 5, 2014 at 8:19:05 pm

Thank you again - I can't believe I have spent a few hours worrying and trying to fix this, if it isn't actually a fault!...

The glitches which appear in Windows media player are not there when I play back on the PC on Cyberlink Power DVD, nor when I put the clip back on the Vegas timeline. So, I must assume it's an issue with Windows media player struggling to decode certain parts, and that when I've had problems before, by bad luck, my own stand-alone DVD player (recorder) also struggles decoding some of those same parts. Perhaps other DVD players would have been fine with it!



This was for the whole video, the most recent render I tried. I don't know why it's calculated it as if it's 50 fps, not 25 fps, so it actually gives average = 6.95 Mbps and max 8.6, which is right. The small spikes do mostly relate to fast cross fades etc, but not to possible glitches in playback.



And this was for a small clip of an earlier attempt. The two "glitches" in that clip I have marked with arrows. The rest of the "spikes" haven't caused any problems.

So, do you think I've done all I need to, to minimise the risk of problems with playback? Or have I even gone too far? Bit rates up a bit, down a bit?

My most recent attempt used:

VBR 2-pass, average 7.0 Mbps, max 8.0 Mbps,
I-frames every 4 frames (is that unnecessary, do you think?)
B-frames only 1 in a row
Closed GOPs

Thanks and all the best, Giles


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Graham Bernard
Re: Glitches in output rendered MPEG2 files
on Apr 5, 2014 at 9:17:53 pm

I'm glad you've found BRV useful It adds that little more to our knowledge of what is going on. OK, you have pointed out the areas of glitches, this COULD be that that they are not as high as the other PEAKS, but that you have several close together. Yes?

Grazie

Video Content Creator and Potter
PC 7 64-bit 16gb * Intel® Core™i7-2600k Quad Core 3.40GHz * 2GB NVIDIA GEFORCE GTX 560 Ti
Cameras: Canon XF300 + PowerShot SX50HS Bridge


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Giles Meehan
Re: Glitches in output rendered MPEG2 files
on Apr 6, 2014 at 7:33:25 am

Yes, it could just be a build up of data rate overload for WMP and some DVD players... So...? I could

- have longer cross-fades or no cross-fades at all, wherever I see a problem
- try tweaking the average and max bitrates further (although I don't want them much lower, for the quality to drop)
- try tweaking the I frames and B frames (but the more I frames and fewer B frames I have, then the *higher* data rate I'd need for actual picture quality, because there's less time-based compression)
- forget about it, and hope that most DVD players will cope with the current file/s, like Cyberlink software seems to manage it?

Any ideas?!


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Steve Rhoden
Re: Glitches in output rendered MPEG2 files
on Apr 6, 2014 at 12:25:44 pm

Thats why i asked, WMP is not always the best judge of
precise playback to use.

Steve Rhoden
(Cow Leader)
Film Editor & Compositor.
Filmex Creative Media.
http://www.facebook.com/FilmexCreativeMedia
1-876-461-9019


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