Questionable Quicktime Movie Sync?

i've been working with QT with logic for about 7 or 8 years now. out of sync audio can be vexing.

logic syncs to the video (frame rate) of the QT video, not the audio. it speeds up and slows down the audio in contiguous sync mode to keep the embedded audio in sync (actually its QT which logic accesses - not logic itself). if you turn off contiguous sync the audio and video will freewheel. in the old days someimtes this was better when the audio would start to fluctuate ridiculously - i mean it used to go from chipmunks to darth vader in about 15 secs when it was really bad.

logic syncing to the video is very accurate, and always has been. some people have complained that sometimes the spmte of logic and the bitc in the film could drift by a frame, but that was only because logic was looking at much greater degree of accuracy than 25 fps. also, you can have dropped frames in the video capture process with old cards that couldn't cope with a spike in data and just gave up on the frame.

i would suggest that your video settings for audio were on contiguous sync, which is why the sync changed each time.

one thing i learnt early on and i'm sure you are aware is that the BITC in your film has to be god, and is the absolute reference. provided you don't have dropped frames in the video (and your capture device should warn you if you do) you should be alright.

sounds like things are pretty solid.

the drift you are getting with the audio is actually pretty tight. exporting the audio into logic is the most reliable method if the sync sound and music has to be that tight which it rarely does until the dub.

your video should be contiguous for best playback, if you are on non-contiguous the audio (in logic) and video will freewheel, but reset whenever you stop and start. it shouldn't be necessary with QT, modern harddrives and computers, and modern capture devices.

if your video was exported from an offline edit, then i don't see how it could possibly have dropped frames.

i have a really old steam powered DC30 capture card which were all the rage when apple switched from NuBus to PCI. they are still a brilliant capture card, and coupled with a driver that has been written in recent years for OSX, it is one of the (many) reasons why i haven't upgraded to a G5, despite rea---lly wanting to.

Hi Rohan,

I've been working with video and audio for years - used to use a SMPTE slave driver in protools - incredibly slow to lock but was frame accurate.
Now QuickTime movies in Logic are a joy to work with but I have had exactly the same issue of the audio in the QuickTime movie fluctuating in sync with the transferred audio in Logic. Firstly the fluctuations I get are probably in the region of up to 8-12 frames (most people underestimate the frame differences - move a cue 1 or 2 frames it's often very hard to notice it.)

Secondly are you saying when the audio discrepancy occurs between the movies audio and the transferred audio in Logic it is the Movies audio that is out of sync with the picture? Instinctively I would be more likely to believe the QuickTime audio is still in sync with the pictures and Logic is adrift. The times I have checked this with lip sync the QuickTime audio is good the Logic audio is the one that is out.

I have tried contiguous sync and non-contiguous and as far as the random lack of sync between QuickTime soundtrack and QuickTime soundtrack that has been transferred and is playing from Logic both settings give similar results.

Unlike a video signal am I right in saying that QuickTime movies which can be any number of frames per second don't actually have frame edges like pro video machines they just stream constant data? So on a 30fps QuickTime file there is no defining frame start pulse every 1/30 second? So there is no particular defining edge to lock the equivalent SMPTE frame edge in Logic.

Is there some sort of video latency!

With the rise and rise of visual media and Logic's integration with it I would certainly welcome a greater feed on information from the experts as to how Logic syncs with QuickTime and can we really rely on it for frame accurate work over say a 60 minute production.

Julian


G52.5/6.5GB RAM Mac OS X (10.4.4) Dual 250Gb SATA, 30" Cinema x 2, Metric Halo Interfaces, 1.6TB SATA Raid

G52.5/6.5GB RAM Mac OS X (10.4.4) Dual 250Gb SATA, 30" Cinema x 2, Metric Halo Interfaces, 1.6TB SATA Raid

greater feed on information from the experts

just to warn you, i'm no expert!

Is there some sort of video latency!

yes! if you are using a firewire device, there can be which you can compensate for in setting within logic, i believe. i have no such latency with my old pci card which has led me to believe that pci cards are superior. however, i am not so sure anymore.

don't actually have frame edges like pro video machines they just stream constant data?

no this isn't correct. each frame of video is (in my case) a jpeg picture which is played back at 25 fps. the capture device is able to syncronize with incoming video source in the same way that a TV syncs with a video. on a TV information is drawn very quickly onto phosphorescent surface. went it has finished a run, it goes back to the top and starts again with the next frame. so a frame on a video tape is a "stream" but a frame on a QT is packet of data.

I have tried contiguous sync and non-contiguous

yeah there's not much difference owing to the accuracy of the computers internal clock. in non-contiguous it plays back logic at 25 fps and the QT at 25 fps and providing there is nothing to cause any problems to the way the computer is doing its calculations they are very accurate, and then reset after playback is stopped. try running a QT film in logic in non-contiguous for 1/2 an hour or more. i am pretty sure when you stop it the picture might jump forward or back a frame or 2. if it doesn't - well, hats off to your system.

with contiguous logic checks in with QT on every frame to make sure they agree. the audio is different to the video in that it IS a stream. so it speeds up and slows it down to keep it in sync. this is in the manual.

i would have thought - and this is me speculating really, that logic would be the best place for really accurate audio since it takes complete control of the audio stream and owing to the nature of video, it would be in complete sync with the picture. i was warned to make sure that i captured my audio with the same device as the video (you can capture the audio for the video on different devices) in order for the audio to be in sync with the picture. but this relates to QT playing back the audio. QT is not as accurate as logic when it comes to audio, i feel safe in saying. however, i have not had any complaints about the accuracy of audio within QT since my OSX driver for the DC30.

my QT implementation with logic is rock solid. i don't recall seeing any noticeable drift in my audio since moving to OSX. surely modern capture devices are as good.

Rohan,

Thanks for the reply,

The big issue I have with Logic and QuickTime is the respective audio sync. A piece i was working on recently had very obvious lip sync near the front. Played in QuickTime stand alone it was absolutely rock solid - must have played it a hundred times! (it was a DV PAL 25fps encode)

Now in Logic almost every time the QuickTime was played there was an offset up to +/- 8 frames sometimes it was perfect sync (well phasing nicely) but more often than not out.

I need to do some more checks but my impression was that it was the Logic audio and hence the whole Logic song lock that was inaacurate each time than the QuickTime audio being out of sync with it's own video track.

Do you think that when QuickTimes are played back in Logic their audio is subsequently less accurate to their own pictures - that Logic degrades the sync relationship within QuickTime.

Perhaps there could be a few tests done - best with lip sync with repeated playbacks comparing the embedded QuickTime sync with the audio transferred to Logic and where there is an obvious diferential between the two audio tracks a visual determination as to which track has lost sync.

Julian

G52.5/6.5GB RAM Mac OS X (10.4.4) Dual 250Gb SATA, 30" Cinema x 2, Metric Halo Interfaces, 1.6TB SATA Raid

i thought about this some more after i posted last night.

it should be pointed out that the reliability of the audio you extract from the QT is dependent on the quality of the audio capture on your video capture device.

it was recommended to me (at least on the instructionmanuals for the card and within adobe premiere) that you should capture the audio with the video capture card for reliable sync. clearly there is some "awareness" in the QT file set up by the QT capture process that gives us the tight sync we see when played back on QT standalone.

the test for picture sync, which is the most critical thing for us, always gives exact results. the BITC is always with the logic smpte unless there are dropped frames.

i have almost always used the embedded audio in the QT playing it out through the 2-track inputs on the desk. i think that contrary to my previous statement that logic would be more accurate playback of the sync sound, i think now there is probably a bit more to the QT file than simple playback of PCM-linear audio and video.

also i should point out that in my experience QT's aren't all the same. some versions of QT run horribly with logic. i remember not being able to use QT 4 through to about half way though 6 until moving to OSX.

Most of the QuickTimes I deal with aren't simple "captures" through a video card but QuickTime exports from pro-edit suites using Avid or Final Cut Pro. At this point the audio video relationship is locked solid with station sync prior to input to the non linear system and a high level of sync is always maintained as a priority.

Just a thought but when you are viewing the Logic SMPTE window are you sure that the timecode displayed here is actually related to the audio (I know it is when Logic runs internally without sync) but could it somehow be linked directly to the QuickTime movie so it effectively repeats the QuickTime timeline. When you've heard the audio in logic pitch as it slews to match the QuickTime have you notice the Logic Timecode slow down or speed up?

What I would like to have is a full technical explanation on exactly how Logic Syncs with QuickTime.

When you press play Logic has to start, audio has to be sourced, buffered etc. The QuickTime file has to be located and started from exactly the same position. If there is a discrepancy between QuickTime position and Logic - does Logic slow down with contiguous sync - I guess the error just remains if contiguous is not selected? - (if it does and the audio interface is on it's internal clock or an external clock how can this be achieved. The SMPTE slave driver used to force the DigiDesign convertors to varispeed their sample rate.
I'm not sure my interfaces have their sample rate varispeeded by Logic.

If instead the QuickTime movie is slowed down or speeded up in the case of say 25fps there wouldn't be exactly 25 frames in a second during this transition.

Questions question questions!


Julian

contiguous sync

the audio is speeded up and slowed down, the video maintains a constant sync.

I'm not sure my interfaces have their sample rate varispeeded by Logic.

logic uses sample rate conversion to control the speed of the audio but the audio is played back through QT. the video is always spot on, at least it has been with my card, although there were times in os 9 when truly bizarre problems occured and the video was unusable until restart.

i have thoroughly checked the video sync over the years and it is absolutely spot on with logic.

does Logic slow down with contiguous sync

no it stays the same and controls the QT movie frame by frame. computers can count the number of frames in a movie file and therefore it is a relatively easy matter for them to work out where in the movie file they should playback from.

but audio is different because it runs in a constant stream, and not image by image. since logic is taking control of the speed it seems that it is necessary for it to take control of the audio sync embedded in the QT file. i am not entirely sure why the sound should need to be controlled by logic, if it is in sync in the QT movie file, but it may have something to do with older less accurate video capture devices. it may be that QT doesn't play back exactly at 25 equal fps, it may be inaccurate and therefore logic, being more precise takes charge of of the frame rate playback from QT and therefore has to adjust the audio to keep it in sync.

i am pretty sure it has something to do with the way logic controls QT that it has to "break" the sync relationship with audio and video track in QT.

i would have thought, though, that an extracted audio file synced properly with the video within logic from a high end source would be really tight.

Hi Rohan,

You keep mentioning video cards but I don't see how there would be any relationship between video cards and quicktime. The workflow I am usually involved in is Film or Video captured, usually seperately from the audio which comes from a different high grade source (DAT, NAGRA SOLID STATE, ETC).

The QuickTime file is made in an online suite and I play it back directly on an Apple Screen (my desktop) So there are no video cards in the chain.

Even on the capture side if you happen to be capturing in a quicktime format I would have thought the relationship with QuickTime would be generated by the host software not the card.

And isn't a QuickTime file just a stream of data - it is the codec that interprets that data (as a constant stream?) and reconstructs the frame content as encoded.

Also is there always a frame base as some quicktime files (MPEG 2 for example) cannot be edited until they are transferred into an editable frame accurate format.

You mentioned that Logic stays time constant but changes the movie playback speed. Surely that means the QuickTime exact frame rate is now no longer the same as the source video in the online suite so how can true sync be guaranteed?

I want to burn an aiff file that I know is in perfect sync with the QuickTime I've been using and more importantly it will be in perfect sync with the OnLine Edit it is laid back into on AVID or FCP.

I think some definative documentation of how Logic is syncing and how it effects frame accurate playback of QuickTime would be very welcome.

Other

going backwards with julian

I think some definative documentation of how Logic is syncing and how it effects frame accurate playback of QuickTime would be very welcome.

i agree.

You mentioned that Logic stays time constant but changes the movie playback speed. Surely that means the QuickTime exact frame rate is now no longer the same as the source video in the online suite so how can true sync be guaranteed?

no. this isn't right. depending on the codec, the video is seen in terms of "packets" of data which correspond to frame rate. but QT won't necessarily playback each frame at exactly 1/25th of a second, it might vary slightly. logic forces it to playback exactly 1/25th of its seconds. this is because the data rate might vary in the video i guess.

but audio is handled differently because it IS a stream. i am not exactly sure how QTs sync its video to its audio other than measuring the number of frames against the number of samples.

Also is there always a frame base as some quicktime files (MPEG 2 for example) cannot be edited until they are transferred into an editable frame accurate format.

muxed video and audio are a different issue altogether because they are bitrate dependant. in this scenario the video and audio are sort of "entwined" - again i'm no expert, but the info is out there on this one. not only that mpeg encoded video and audio is also dependant on the codec of the original material. for example and mpeg-1 will not play if it was created with sorensen 3 if the sorensen 3 codec is not installed on the system. mpeg is a muxing format not a codec - if i understand this correctly and i am pretty confident that i do.

And isn't a QuickTime file just a stream of data - it is the codec that interprets that data (as a constant stream?) and reconstructs the frame content as encoded.

it is entirely dependant on the codec. consequently there ARE all sorts of syncing issues which relate to audio and video with certain kinds of codecs. incidentally, it is generally considered a good move to use a low compression codec like DV when using logic unless you have a capture/playback card, because it is less work for the computer to decode. they greater the encoding generally the greater the strain on the computer. that said, it again dependant on the codec. some are really efficient at the decoding end such as h.264 which can give you really good quality video for relatively little cpu strain and very small file sizes.

Even on the capture side if you happen to be capturing in a quicktime format I would have thought the relationship with QuickTime would be generated by the host software not the card.

sort of - it is generated by the codec (in this case coder) which comes with QT and the capture device. i use miromotion jpega, which gives me extremely good results at a data rate of about 1.5 Mb/s. i play this back (i have to use this codec for the card to do the decoding - or else the computer will do the decoding) through the card and out on to a normal TV.

You keep mentioning video cards but I don't see how there would be any relationship between video cards and quicktime.

well, the video cards use QT as the format for the digitized video. they have to talk to each other regarding the unpacking of the compressed video data. therefore their relationship is critical. i remember absolutely not being able to use certain combinations of OS, QT, capture card driver.

if you are getting the QT from such a high end source, then depending on the codec i am sure that they should work solidly with logic.

to be certain of your aif file being exactly right with the film, you have to go by the BITC. if the file is being played back on a system synced to the video then the video will be set to chase the audio system and the event that you had at 567464 samples into your cue corresponding to 10:23:44:67 will match.

i have delivered this way for years with nary an issue.

there was recently a post on the 24.97 frame rate you see in some QT files is because of the dropped frames. the specified length of the file doesn't quite correspond with the specified frame rate.

try this play quicktime and go apple-i. you should see the framerate display showing you the frame rate of the file.

it is strange that the warning is disabled, but maybe logic does the calculations necessary to make them correspond. its just maths after all - computers do maths pretty well.

logic syncs to the computers internal clock. 44.1 khz is 44100 samples per second. the internal clock is pretty accurate i guess since we all use it. wordclock syncronization with something like bigben from apogee is supposed to improve sample rate accuracy and therefore quality. hmm - i doubt whether i'd notice the difference.

QT playback - it has its own video and audio components which logic accesses in order to give you video and audio via quicktime.

As the previous poster wrote, I'd like to get an exact description of Logic's QT playback/sync mechanism.

that's fairly clear - but i would like to know more about how video and audio relate to each other in a QT movie. although i know its dependent on the codec.

Hi 2 all,
I'm just recently experiencing Logic 7.1.1 playing a DV 25 PAL stream that I exported directly from FCP in the way that has been described up ther somewhere: With every start it plays back differently - must be around +/- 5 frames maximum.
To bring in some more information, right now I am doing ADR, so I am quite experienced with detecting whether it's "on" or not. Normally I can tell the audio to be off one frame - and the direction in which i have 2 put it. That's just experience. And of course I am not dealing with a problem of different timecode formats or the mains not plugged in...I know what I am doing. When I go start checking the forum I triplechecked all dumbness factors long time ago...
The relevant thing is here, that I am not comparing embedded audio of the DV (there is none in my case) to exported audio. I can clearly see it without that.
Fact IS that Logic plays back the movie randomly synced, which makes it virtually unusable.
Sometimes you can even see it at stopping, when the stamped-in TC of the picture is different from Logic's TC.
I can remember this working properly about a year ago when I did this last time. Of course on a system that was up to date back then, means Logic Pro 6.4.3 and OS X whatever, and of course QT 6.x.

Rohan, sorry, I appreciate your trust in computers and Logic, but theory is not really helping here, nor is speculating, means : "guessing", about how Logic and QT might work - or "should".
This is a problem and everyone who can be of help, regarding further insight on this is GREATLY APPRECIATED !
As there is : Is this reproducable, is there some settings that can reproducable changes in this behaviour, is there any knowledge whether it has something to do with different QT formats, e.g. export settings ?
I am trying to work out of LAP 6.4.3 now, trying to find out what happens there. As I know that version to be working, if it's not anymore, I know it must have something to do with QT 7 or maybe 10.4.6 which I unfortunately installed right before I started on this project. Also I have to find out if this happens in FCP, too. If yes it's one more hint towards QT or OS X.
Will post my results soon.

This thread is not very helpful if it continues ignoring the facts, assuming that computers should be able to calculate mistakes away.

Come on let's get this down !
spocintosh