software to analyze transcoding problems

[ezu0526]

Hi,

Newbie, sorry if this is wrong forum. I've looked for this question elsewhere but haven't seen anything on the subject. Is there a way to use a particular piece of software to anticipate or predict when part of a transcoding has gone wrong? I'm having problems synching up soundtracks on various avi's of movies & tv eps, but I feels like I don't know why something goes wrong when it does go wrong. There are logs for Nero that go on for hundreds of kilobytes of data, but... how much of that is useful? Where do I go to find out about this?

It seems something--Gspot, VirtualDub, Gordian Knot, Tmpgenc--some one of this kind of program or combination of them--should be usable so after I've tried to convert something, I can use such a prog to look at visual data or a log file & say, huh, this portion of the file here is missing data or screwy so maybe I should try X or Y to make it better before burning a DVD.

If I'm not asking the right questions please help me understand which ones I should be asking (or if this is pointless & just will make everything more complicated). Thanks for any suggestions. Esp ones that do not involve getting an advanced degree in math or programming; I know there are movie freaks out there making really nice copies of stuff for themselves, so... it must be possible.

[guns1inger]

99 times out of 100 it is a combination of user skill level and VBR MP3 audio that result in audio sync problems. You can scan for bad frames in virtualdub, and sometimes this will cause problems, but mostly it is a matter of using the right tools for each stage of the job. The right tools do not include WinAVI, NeroVision, DVDSanta etc. ConvertXtoDVD mostly does a better job, but even it can be stumped by some audio encoding.

The best method involves converting the audio track into uncompressed PCM, encoding it seperately to AC3 or mp2 for your DVD, encoding the video seperately, then bringing them together at authoring time. Sometimes adjustments need to be made. These could be as simply as adding or subtracting a delay to the start of the audio, or alterations to the length. In extreme cases the audio may have to be ediyed and reassembled in order to fit. And sometimes it just cannot be done.

There is no tool that can predict if you are going to run into these problems. If there were, it would be built in to encoders so they could adjust for it and stop it happening.

You basically have three choices

1. Stop downloading poor quality avis and buy the DVD instead.
2. Learn to do all the manual steps involved, which will give you a much higher (but not perfect) success rate.
3. By a Divx certified DVD player, burn your avis as data discs, and stop converting.

[redwudz]

I'd agree completely with guns1inger. Nice answer, BTW.

Sometimes a video with sync problems is the result of a bad cutting job that leaves out some frames when it's been split into several parts then rejoined. Other times it's just missing frames or audio because of transfer errors.

Or it may have been converted from PAL<>NTSC and suffered a poor conversion. Or was encoded badly from a DVD rip to a format like Xvid without using the proper tools.

MP3 VBR audio also causes problems, mainly when re-encoding to a MPEG format. If you check the video first with Gspot 2.60 for VBR before encoding, then convert it to PCM, as guns1inger mentions, you can usually avoid some of those sync issues.

The two types of sync problems most often seen are caused the audio and video lengths not matching, or the video and audio starting at different times. You can fix the first by adjusting one of the lengths. You may be able to check the lengths with VirtualDub. The second requires changing the offset time between the audio and video. VD can also do that.

You can try the easy fixes, but if they get nowhere, it's often not worth much more effort. Especially when you get a blend of both of the above problems all in one file.

BTW, this is always the right forum if you are in doubt.

And welcome to our forums.

[ezu0526]

2. Learn to do all the manual steps involved, which will give you a much higher (but not perfect) success rate.

Hi & thx for your response. Can you suggest which progs are best to learn to use for the specific steps you outlined, please?

And thanks for the welcome & explication, redwudz! Further details always helpful.