Stupid Audio Delay Question...

[DoctorM]

Not a n00b, but a n00b question.
I'm having a brain fart about audio delay and I cannot sort it out with Google.

Audio Delay is being reported as positive 25ms.
I know at 23.976fps that's 0.5994th of a frame.

Not worth mentioning, but I figure that rounds closer to 1 frame than not.

Anyway... if I'm using editing software, do I drag the audio clip 1 frame to the left (and recreate the 1 frame delay) or do I move the audio file to the left to remove the delay?

[Emulgator]

Positive delay -> the muxed-in audio is reported to be later than video ->
you will want to hear audio a bit earlier, so in NLE timeline audio got to be shifted to the left.

Once in an NLE you may lipsync the waveform anyway to events like claps, doorslams, shots, whatever maybe available.
Some editors allow to shift audio in finer granulation than frames.

[DoctorM]

Exactly, it is an NLE editor timeline. My first guess was to slide the audio to the left, but it just felt wrong (maybe because negative delays seem more common). For a half to 1 frame difference, I wasn't sure I'd be able to sync it by ear.

Thanks.

[sneaker_ger]

Positive delay -> the muxed-in audio is reported to be later than video ->
you will want to hear audio a bit earlier, so in NLE timeline audio got to be shifted to the left.

What makes you think that the muxed-in audio is asynchronous?

If they are in-sync (and the audio track starts 25 ms after the video track) and you demux (removing the video/audio timecodes) and later remux again using your NLE editor, you would have to drag the audio to the right, IMHO.

Now, it all depends on how the softwares work and what you understand by "the audio has 25ms of delay" (i.e. has this 25ms of delay already been accounted for (drag to right) or not (drag to left, for example encoder delay)).

[DoctorM]

So, sneaker_ger's comment not withstanding, Emulgator has the right answer?

[manono]

Why not remove the delay entirely using DelayCut and not have to worry about what direction to move it in the timeline? If it's something other than AAC or MP3 (for major audio formats), DelayCut should work.

[DoctorM]

I intend to trim the extra... in my NLE. Seems silly to use an extra processing step if we can just agree which way it gets edited.

[manono]

Sure, do it any way you like. Since it's meant to be delayed 1/40th of a second to be in synch, then sneaker_ger is correct and it should be moved to the right. But if others come along and say this and that, you might regret having asked for advice about which way to move it on the timeline and realize you maybe should have taken the 10-15 seconds to get rid of the delay altogether using DelayCut. Also, since you seem to be saying your timeline can only delay by video frame lengths, you might also get a more accurate synch by using DelayCut on it (maybe depending on the kind of audio).

[DoctorM]

Wait, manono, you are saying that Emulgator is WRONG and sneaker_ger is correct? In a non-linear editor, the audio clip should be slid to the RIGHT in order to be correct?

I'm trying to get my head around that. If the audio file contains a 25ms delay, wouldn't Delay Cut TRIM the first 25ms (in effect the same as sliding it to the LEFT in a video editor)?

I thought this was something simple I wasn't tracking on, but it sounds like everyone has a different opinion.

Edit: Okay, I'm convinced. Still hard to keep straight, but entering a "Start (msec)" of 25 in delaycut it says "Start Frame -1".
So in an editor it is to the right... or just fix the delay before starting.
Thanks for sorting me out.

[manono]

If the audio file contains a 25ms delay, wouldn't Delay Cut TRIM the first 25ms
No, it would add 25ms of silence to the beginning. It depends on the kind of audio, though. If AC3, I think it would be 32ms. If WAV audio, then you'll get the 25ms. I don't work with NLEs at all. I do, however, work with audio delays and DelayCut with some frequency

[DoctorM]

Agreed. It appears 1 frame of silence was added. The source was ac3.

Thanks again. I didn't mean to argue, it's just conflicting answers from others confused things.