T1i Audio sync Problems

[Madmoose]

So at work, we got the new Canon t1i's to shoot shows with, based on the most bang for the buck. and i have to say the image quality looks great, but we're having some serious sync issues, we record the audio seperatly to a digital recorder and we record at standard 48khz,

It starts off fine and synched, then gradually gets more and more out of sync.

Just wondering if anyone has experienced this problem, and if they fixed it?

I should mention, I'm editing in Final cut and was using the cameras naitive codec to edit in, to save time, i've since just cut the audio up and synched it by hand, weirder still is the fact that upon being exported the sync went out again.

Any one who's had this problem please let me know if you fixed it, or if there's a work around.

 

[AndrewGentle]

This often happens when recording independent split system sound. The easiest way to get it all back in synch, assuming the drift is constant, is to pick a synch point at the start and another at the end and stretch the audio recording to match the two points.

 

[Alex H.]

So at work, we got the new Canon t1i's to shoot shows with, based on the most bang for the buck.

The T1i is not a new model. While still available, it was surpassed by the T2i some time ago. If you're talking bang for the buck, the T1i is challenging since it shoots a lousy 20fps in 1080p. If you're fine working strictly in 720p30, then the T1i will work. Now, back on topic...

and i have to say the image quality looks great, but we're having some serious sync issues, we record the audio seperatly to a digital recorder and we record at standard 48khz,

It starts off fine and synched, then gradually gets more and more out of sync.

Just wondering if anyone has experienced this problem, and if they fixed it?

As Andrew alluded, this is a known issue. It's not a product of double-system sound per se. What causes this is a difference in clock between the camera and the audio recorder in certain (and in most low-budget) systems. There are recorders that won't drift as much, and the best way to solve it is through a shared clock between camera and recorder (not possible with DSLR setups). While both may technically record at 48kHz, one may actually clock slightly faster than 48k, and one slightly slower. This will cause drift over time.

So the solution is either to time compress/expand the audio to compensate, or to stretch/compress the video.

I should mention, I'm editing in Final cut and was using the cameras naitive codec to edit in, to save time, i've since just cut the audio up and synched it by hand, weirder still is the fact that upon being exported the sync went out again.

Any one who's had this problem please let me know if you fixed it, or if there's a work around.

Why on earth are you editing the native h.264 files in FCP? This is not something that Final Cut is designed to do. And while there are NLEs that offer native h.264 editing support, the fact is that h.264 is not an editing codec by any stretch of the imagination. It's a GOP codec (Group Of Pictures), meaning that it doesn't actually record 30 frames per second. it records an iframe every so often, and then on playback the camera or computer fills in the blanks. If you cut in between iframes, you cut out "point A," leaving the computer to make its way to "point B" without a starting place. Use an iframe codec, like ProRes LT. Or, if your system cannot handle ProRes, use DVCPRO HD.

Use Compressor, or download the free MPEG StreamClip, to batch convert the h.264 files.

 

[MarcusarilliuS_IRL]

I'm editing in premiere CS5. Should I also convert the h.264 files first? If so, what format and settings would you recommend converting the clips with mpeg stream clip?

Thanks.

 

[M. Gilden]

I haven't really tried to use a T1i for video, but I was under the impression that the t2i was the first model with the more standard video frame rates. That being said, if the camera is recording an improper frame rate (like say, 20 fps) and the editor treats it like a standard one (like say, 24 fps), the video will actually play back at a different rate than it was recorded.

I've heard this is true when converting film (24fps) to PAL (25fps). Since the frame rate is 1fps off, they'd have to occasionally double a frame, which would stutter the motion in order to keep the exact timing. Instead, they just sped it up a little to match the 25, including the audio. The difference in speed is so negligible that you can't really tell the difference when you watch it... however after a 2 hour movie, the PAL version will have finished entire minutes before the NTSC version!

In any rate, this is why it is important to use equipment and software that adhere to standard specifications, and why still cameras in movie mode weren't really treated like video cameras until recently.