Loss of audio-to-video sync when rendering

kaycee wrote on 6/14/2003, 6:59 AM
I have been unable to render any video media longer than a minute or two without complete loss of audio-to-video synchronization. I am trying to clean up some old MPEG-1 files, and while everything is AOK in preview, the rendered file goes from in-sync at the beginning to a second or more out-of-sync at 20 minutes. Even a two minute sequence shows some drift out of sync. The audio is always ahead of the video at the end of the sequence. The very basic Windows Movie Maker and Roxio Videowave do not display these tendencies, so I have to believe this is not a system problem.

Is this a known bug, or am I missing something in the settings?

Comments

rebel44 wrote on 6/14/2003, 8:59 AM
I render few live concert videos capture from satelite TV and founs no problem with A/V sync. I had Roxio VideoWave 5 and had problem with sync, but not in Vegas. The reason could be that you have all done on one hd. The basic is that you have OS on one hd and video capture on second because of virtual memory being written to hd constantly and interfere with rendering. Vegas require a lot of resource from system.
Make shure that HD is not fragmented.
Again A/V sync is not a Vegas problem most likely your hardware.
kaycee wrote on 6/14/2003, 10:35 AM
...rebel44... I agree that what you've said is possible, except that my OS is on a separate hard drive, have 1M RAM in addition to a separate 40G drive dedicated to virtual memory, and I am rendering the file to a SCSI 15,000rpm drive designed specifically for A/V production. Basically, I have a PC designed for A/V - with a lot of high-end software as well. I can run as many as 50 audio tracks at once using Logic Audio Platinum without the first hint of latency. This is the ONLY program to date I have had sync problems with.

I have determined that there is a small discernable difference in the compression rate between Video and Audio. It does not matter which format - or quality of resolution - I use for rendering. It is most likely possible to compensate for the error using "time stretch" on the audio. However, I have to say that this basic problem is dissapointing considering the price of the product. I have used other Sonic Foundry products for years and generally considered them excellent.
mikkie wrote on 6/14/2003, 10:39 AM
FWIW and all...

Some folks have reported prob going from mpg1 or 2 encoded with something else, to mpg1/2 in Vegas. I think in most cases rendering an intermediate avi or frameserving cleared those up. In general, no one's reported prob with Vegas maintaining audio sync itself, so not aware of any tendencies in this regard.

General stuff that might help... mpg1/2 use a separate stream for audio, so playback sync prob on a PC aren't uncommon... The FAQ at http://www.nwlink.com/~zachd/ I think includes some interesting info on the mpg audio decoders in windows, how you may have the file to encode/decode a higher range of bitrates, you may not be using it... Sometimes the old trick of splitting the file on the timeline at regular intervals helps - if Vegas has to render the video (if the source is mpg1/2, wmv etc.) before encoding, this might help establish reference points if it's having prob.
SonyEPM wrote on 6/16/2003, 8:43 AM
what format is the original video?

what are your render settings?

how are you viewing the rendered files?
rebel44 wrote on 6/16/2003, 10:55 AM
I have 1G CPU with 256M PC133 so it is not the best system ,but like I said I never encounter and sync problem. I render few captured MTV(capture concert on VHS and then cut each song or 2 and render) and never had sync problem. I render in mpeg1
,MPEg2, AVI and VMW. As I watch I listem and never saw any out of sync problem.
One time I convert from MPEG to AVI by other program and had sync problem visible, but when I drop to Vegas it sync correct. Vegas corrected the sync problem.
That is the reason why I do not believe that Vegas can do bad sync.