HD Audio Drift

[Christopher C. Murphy]

Huh, I've never heard of that before.

How many people have had audio sync problems with the HD10u?

Murph

[Tom Roper]

I'm a veteran of the sync wars when recording tv programs to DVD disk. The audio gets out of sync when I make frame accurate cuts (editing commercials out) on the time line. The fix was to abandon frame accuracy, and make cuts on the I-frames only, not the B or P frames. The DVD 15 GOP (group of pictures) structure is I-B-B-P-B-B-P-B-B-P-B-B-P-B-B. Obviously, if you only edit on the I frames, your frame accuracy is only 1/2 second, but it's preferable to out of sync audio.

I think using well behaved software is the key. I shot a couple hours of video on the GR-HD1, that after editing, was 27 minutes long. I used the included MPEG Edit Studio Pro to make a zillion edits, cuts, joins and insertions on the mpeg2-ts time line. It was very tedious and clumsy software, but to its credit maintained audio sync throughout. It was easy to judge, with video of chirping birds, an audio sync problem would be easy to spot.

Upon downconversion from mpeg2-ts 1280x720 30 fps progressive to DVD NTSC mpeg2-ps 720x480 don't do any further edits/cuts/joins/insertions except on I frames...best not to do them at all since accuracy is only 1/2 second on I-frames.

The other key is finding reliable software...lots of junk out there for DVD editing. The most dependable I've found for DVD is TMPGEnc. Womble is hit or miss. It has an incredibly efficient user interface, fast scrubbing, but unfortunately, all too often screws up the PTS or timecode when using it for frame accurate edits. It has some good utility, de-muxing streams, transcoding from mpeg2-ts to mpeg2-ps without re-encoding works well, but I avoid the frame accurate editing due to constant audio sync and timecode problems.

You can fix audio drift with Gold Wave "Time Warp" but it's easier to just avoid the bad editing habits which create sync problems in the first place.

[Tom Roper]

Another area where audio sync issues get introduced is when transitions, fades, wipes are inserted into the DVD time line. The video has to be re-encoded a few frames around the transition. Too many of these and...wha-lah...sync has shifted.

Again, it's probably just me, but I prefer to use the basic fades built into the camera, if any...versus taking chances of introducing audio sync problems in post.

I have not tried using transitions with the included MPEG Edit Studio Pro, because I don't want any re-encodes except the ONE necessary when downconverting to SD-NTSC to produce a DVD. (I use TMPGEnc for that.) MPEG Edit Studio Pro will let you do the basic cuts, joins and insertions to the mpeg2-ts without re-encoding. It's primitive, but reliable.

[David Kennett]

I agree - KDDI software good on timing.

The DV audio (locked or unlocked) has no long term affects on timing.

Concerning GOPs and timing. To meet HDV and DVD standards, each GOP must include in its data header the number of frames in THAT GOP. (The MPG standard allows a single header at the beginning stating the number of frames - but then they must all be the same.) When the encoder encounters a cut, it immediately starts a new GOP with an I frame. It then must go back to the previous GOP (that it has cut short) and ammend the header.

On the KDDI editor, if you click on one of those frames running just below the picture monitor, you can see nearby frames. In a corner of each is a color dot. White is an I frame, and red and blue are B and P frames, but I forget which is which. You can see that the normal progression is altered around edits.

If you think about it, that's why in-camera edits are not proper in the HD10. It would be tough to go back to the tape and change the last header already recorded.

[Christopher C. Murphy]

So, shooting and capturing TS streams that get converted to a new codec (in my case DVCPro HD) doesn't automatically lock the clips audio?

I thought it did...but, from what you guys are saying if I have a long clip and I've encoded it to a different codec the audio drift remains.

Sounds like you guys are all on PC? It must be the same for Mac users?

Murph

[Tom Roper]

- Murph, my observation is no problems going to a new codec.

The problem is editing within a 2ps codec on non I-frames. The KDDI software seems immune to editing problems on the 2ts stream, even frame accurate on non I-frames seems okay.

As David mentioned and my observation is the same...the KDDI software for frame accurate editing on the 2ts has not caused any audio sync problems for me. Other programs doing frame accurate edits on the 2ps have caused sync issues for me, and so I avoid the frame accurate edits altogether, opting instead to cut on the I-frames only in 2ps.

To summarize:

Converting a 2ts to 2ps, no problem.
Frame accurate editing with KDDI on 2ts, no problem.
Frame accurate editing with anything on 2ps, at your peril.
Editing on 2ps I-frames, no problem but not frame accurate.

Accordingly, I do things in this order:

Basic cuts/joins/insertions with KDDI on the 2ts.
Copy the edited 2ts back to mini-DV tape for archiving.
Re-encode the 2ts to 2ps 720x480 with TMPGEnc 3.0 Xpress.
Author and burn DVD from 2ps with TMPGEnc DVD Author.

Legend:
2ts = mpeg2ts (HDTV transfer stream)
2ps = mpeg2ps (DVD compatible program stream)

Everyone has their own particular methods and techniques. I'm not stating mine are the only workable ones, just to emphasize that audio sync problems are not endemic, and CAN be avoided. The main audio sync pitfall I've encountered is making cuts/joins/insertions on non I-frames within the 2ps editor. Avoiding that pitfall, sync remains good. Your mileage may vary.

[Tom Roper]

And re-reading your post Murph, I would say your audio sync problem is not caused by going from raw camera footage TS to DVCPro HD, but possibly is caused by the editing you do afterward once within the DVCPro HD editor.

The (6) GOP format for HDV is I-B-B-P-B-B. If you don't have any audio sync problems with the unbroken stream in DVCPro HD, then the next step would be to see if the audio sync is maintained by cutting on the I-frames only. It's not frame accurate that way, but the penalty is not so severe as with the 15 GOP DVD structure, since your accuracy is now 0.2 seconds.

This has no bearing on the original poster (Ben) can't keep synchronized the TS to DAT...different problem.

I can only comment my observation and experience, which is to edit carefully to avoid audio sync problems, even if that means the edits are kept simple and non-sophisticated. Audio sync problems are very distracting and serious. The audio may start out "locked," but careless editing can unlock it for sure.

As you have by now surmised...I use the PC environment.

[Christopher C. Murphy]

Tom, thanks for all the great infomation.

My FCP HD import of DVCPro HD is 29.97 frames for sure. When I edit it does the drop frame thing, so I'm thinking that it should be ok. Just a suggestion, but when you guys import into PC's why not convert ASAP to a locked codec or do you need your existing system path the same? It sounds like you have more work than me and I thought the Mac users had the sucky HDV route. (LumiereHD has solved the main problem though)

Murph

[Tom Roper]

I just do it as a hobby, so playing within the constraints of budget software is all that's justified for me. (But I still won't tolerate bad audio sync, and fortunately, it isn't necessary to.)