A couple of Newbie Questions

[squeed]

I am closing in on getting the audio to sync with the video using ffMpeg. Here are a couple of things that I have learned coupled with some questions that I need answers to.

What I have learned

When trying to make a VCD/SVCD you can't trust QT or VLC to play back your work because they both offer different results.

What I don't understand

1) How does 41,000 vs 48,000 etc ... play into audio compression and does this matter for syncing the video. What exactly are you doing in ffMpeg when you adjust these settings ?

2) How do the other settings like 192 or 224 etc ... matter ? What exactly are you doing when you set these in ffMpeg ?

3) Why does 4:3 or 16:9 matter? Do they effect the audio sync ? Also when using Mpeginfo on my VOB it tells me that I have a 4:2:0 Chroma format. What does that mean as far as my audio sync ?

4) 29.976 vs 23.976 etc ... What am I supposed to do here ? Do I match what MpegInfo tells me my VOB source is or do I go less ? Every VOB source so far says 29.976. Does this matter for the audio sync ?

Finally, on my last attempt at using ffMpeg going from VOB to XVCD, the video quality was excellent, but as usual the audio was not in sync, however the audio was very fast. Meaning everyone was speaking quickly. This was encouraging because up until this time nothing I did effected the audio in any way other than making it faster or slower than the video. When I say faster I mean "ahead of" and when I say slower I mean "Behind" This time the audio itself was actually effected. The audio sounded like you were playing it at twice its normal speed. So this leads me to believe that I may be able to make an insync VCD/SVCD if I can understand how to control it.

-S

[squeed]

Anyone ?

[Poplar]

1. Don't what ffMPEG is. Everyone here uses TMPG or CCE for S/VCD. There are a lot of guides out there proven to be very good.

2. 44100 or 48000 sample rate doesn't matter. Almost all DVD players can handle both. Has nothing to do with synch.

3. YUV 4:2:0 is color format of MPEG-2 in Main Profile@Main Level.

4. 4:3 or 16:9 is the aspect ratio of the source.

5. Frame rates have a lot to do with synch. Be careful with them when you convert one from another, you can easily screw up synch if you don't know what you are doing.

It looks like your problem is A/V synch. These kind of questions have been asked hundreds of times. My advice is that follow a good guide and understand what you are about to do, everything will be fine.

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oops, sorry.... Didn't notice this is in Mac Video forum. My apology.

[dwoodusa]

Here's a reply to a previous sync post :

Disclaimer: All of the facts may not be correct. These are only my thoughts on the subject, in fact, I may be showing my own ignorance. I invite any corrections and/or comments.

In discussing the sync issue with some of the top hacker in the mac community, qt mutator is not the correct way to fix the problem. At least for now, most of the tutorials include mutator.

Note: the length of the audio should be used as the baseline, and should never be changed. If the length of audio track is 60 mins (always use this as baseline), then the video was originally 60 min also. If the sync is off by 12 mins at the end, then [60-12=48 : 48/60=0.8 : 23.976/29.97=0.8] Another way to look at it is: if the original video was encoded at 23.976 fps it would be about 86313 frames [23.976 fps x 60 sec/min x 60 mins = 86313]. If you play those 86313 frames back at 29.97 fps it would only play for 48 minutes [86313 / 29.97 / 60 = 48]. Get the idea.

In general, there are four types of dvd. 1) made for video ntsc (29.97 fps), made for film (24.0 fps), converted film ntsc (23.976 fps), and pal video and converted film (25.0 fps). The trick is to pick the right one. Not much problem for video ntsc or native film, or even pal. Where it get tricky is the converted film to ntsc, which Hollywood uses allot. They take film (24.0), drop some frames to make space for the signals TV needs (23.976), then tell the dvd player to add frames to make it look like video (29.97). This process is call pulldown and there are settings in the encoders for this. But most decoders have trouble with it, because the info on the mpeg says it's 29.97.

There is more! If the producer includes animations or special effects, these could be at totally different frame rates, switching then switching back.

If there was a lead-in video clip that you did not rip or the
soundtrack starts before the video, the offset in mplex can be used. In this case QT Mutator offsets works great for mov.

At the present time, there is no decoder/encoder that gets it right all of the time, including apps for the PC. There are talented people working to solve the puzzle. But even the experts I have talked with only try a dvd title once or twice, then go buy it for $19.00 if they really want it.

This wasn't the answer you were hoping to get, but I hope it helps,
RNC

Confusing huh !
I had major problems trying to sync Monsters Ball (5Days), I eventually gave up and trashed it

"2) How do the other settings like 192 or 224 etc ... matter ? What exactly are you doing when you set these in ffMpeg ? "

I guess you are referring to the Audio bitrate setting. This will affect the quality of the audio and the total bitrate of your movie.
ie : VCD compliant = total bitrate of 1150
therefor if your audio bitrate is 128? your video bitrate shouldn't be more than 1022.
It all depends on what you want to do with the movie ie DIVX / VCD /XVCD /DVD

4) 29.976 vs 23.976 etc ... What am I supposed to do here ? Do I match what MpegInfo tells me my VOB source is or do I go less ? Every VOB source so far says 29.976. Does this matter for the audio sync ?

I don't think FFMPEGX/ MPEGInfo always reads the framerate correctly Ross's post above should give you some idea why.

It seems your problem is probably video framerate try different framerate setting when you encode w/ ffmegx.
Or just trash the B%^&$&% and move on

PS
I wanna use the same disclaimer as Ross

PPS
Here's a link to a VCD/XVCD tutorial that is supposed to work ( I haven't tried it) : http://homepage.mac.com/rnc/