real quick ?

[jrg]

i am blind from re-reading the guides, but still cannot find my answer.

After a DVD2AVI project, it has a delay embedded in the AC3 file name. What program and when do you enter this delay value?

I have only burned about 6 movies using the Trilight guide, but this is the first one that has a delay value associated with the AC3 file.

[jrg]

burned the movie anyway. did not notice any offset between picture and audio.

Just curious why the guides make note of the delay and if it is used anywhere.

Anyone know?

Thanks

[rjgn]

Yeah I noticed this too. The guides tell you to note the delay but never actually tell you what to do about it!

I've done a few where I've been given the delay info from DVD2AVI but I've always ignored it and never had a problem.

[TRILIGHT]

The delay value must be used in other procedures since it will be off by that much. There are timecodes embedded in the AC3 file that sync's it up with the video when you place it on the timeline in Maestro. That's why you don't have to worry about it. I've run into some more complex scenarios which required using software such as Scenarist where I had to use the delay to correct the offset.

I wouldn't worry about it until you run into a problem. Just remember what you read and don't post something saying "my audio is out of sync! What do I do?" cause ya already know the answer. hehe ;)

[Matthew]

TRILIGHT, I did a test using Ocean's Eleven (R4 PAL). I imported the extracted video stream (not re-encoded) into Maestro. It had a timecode a bit less than an hour. Anyway I imported the AC3 which had a delay of -96 according to DVD2AVI.

I compiled the project and DVD2AVI reported the delay on the AC3 as -80ms (16 ms off). I don't think it's a coincidence that -80 is a multiple of 40. 40 ms = 1 video frame in PAL.

Also, the time stamp in Sonic Foundry Soft Encode only goes as low as 1 frame (which in the case of PAL is 40ms). So that would indicate that time stamps are not really accurate.

Anyway I know using the method I outlined here: http://forum.doom9.org/showthread.php?s=&threadid=20433

results in sync that is 1 ms off at worst.

Maybe I'm missing something :confused:

[ronnylov]

Can you really notice if the audio is off by one frame or less?

[TRILIGHT]

Not sure I understand what you may or may not be missing, Matthew. I don't see a question really in your post. I'm interested in knowing how you're testing your audio and video to know that you are off by 1ms. I do not believe a difference of 1/1000th of a second is perceptible by human eyes and ears.

[mpucoder]

That would have to be a long term error averaged over the entire film, since even the shortest video field is 16.7ms. Some test results I read years ago stated the shortest error a human could perceive was 100ms, and average viewers can tolerate up to 500ms.
SMPTE allows not more than a 2 frame error.

[Matthew]

TRILIGHT I'm relying on DVD2AVI + the assumption that AC3 delay corrector cuts properly (and there's no reason to believe it doesn't - Maestro doesn't complain about incomplete frames). [BTW I'm not complaining about the 1 ms, I know its impossible to tell the difference].

My point is that just relying on Maestro means that the audio could be off more because the delay can only be in increments of 40 ms (PAL). Maybe I'm incorrect in relation to this, I'm just putting my interpretation forward.

"Some test results I read years ago stated the shortest error a human could perceive was 100ms, and average viewers can tolerate up to 500ms."

Recently I noticed a film I encoded was out of sync. As I recall it turns out the audio was off 80ms (and a French film as well), so I'm not sure about that.

Also mpucoder, I've made a re-authored DVD where DVD2AVI reported the delay as 15 ms, which is less than 16.7 ms.

In practical terms this may all be irrelevant because of humans can't tell the difference, but some of us are anal retentive about achieving perfect sync, as compared the original DVD =)

[hoops10]

If you are using Maestro or Scenarist for DD tracks, then don't worry about the audio offset. The only time I've had to manually mess with the audio offsets in Scenarist was when dealing with a DTS stream. Or perhaps a Warner Bros. movie!