Audio and video out of synch in FCPX

I have been doing simultaneous live broadcasting and recording of church services.

Previously I used a Vixia HV30 for capturing the video which was input into a Mac Mini via Firewire port. The audio was input into the Mac Mini via an Audio Technica USB interface.  Using Wirecast, I broadcast the live service while simultaneously recording to hard drive as a .mov file. This worked fine. I imported the mov file into FCPX  and did my editing with no problems with audio/video synchrony.

In an attempt to improve the video quality of both the broadcasts and the recordings I replaced the Vixia with a Panasonic HCX920.  I record the video directly to the SD card in AHVCD format. I record the audio two ways.  I record it to the Mac Mini through Wirecast and I record a direct feed of the microphone output to Sound Studio app.

I import the video into Final Cut Pro X and transcode it to ProRes 422.  I import the two audio sources into the same event so that I can determine which is best.  In FCPX I synchronize the beginning audio/video with clapboard synch.  It becomes immediately obvious that the audio and video progressively lose synchronization across the timeline. The audio recorded with Wirecast is actually off the least amount with perhaps only about 1 second difference between audio and video over a one hour recording.  The audio recorded by Sound Studio is off by a much larger amount.

I was very pleased to find that I could restore synchrony in the FCPX timeline by using the "Retime editor".  This allowed me to synchronize the end of the recording and maintain synchrony over the entire recording.  I can play through the entire one hour recording in the FCPX timeline and there is perfect synchronization!   BUT–– No matter how I try to export the final edited project the resulting output displays major a/v dys-synchrony.  The same is true if I send the project to Compressor for encoding.

What am I doing wrong?  I apologize for this long post but I felt that anyone attempting to help me would need at least this level of background.

John 

Most of the time this is the audio sample rate being different than the Timeline audio sample rate. Be sure both are set to 48kHz.

Thanks BenB

You have confirmed one of my assumptions (that sample rates should be the same). I'm really not very experienced with audio recording technology.
I've already checked and made sure that the sample rates are 48kHz. The audio recording made with Wirecast has such a minimal amount of dys-synchrony with the video that I can deal with it fairly easy.
However, the gradual "slowing" I see with recordings made with the Sound Studio app results in about 4 seconds or so mismatch in a one hour recording. This makes audio recorded in this fashion essentially useless. Perhaps I'll try a different application for recording the mic input to my Mac.

I'm having similar issues with exports not reflecting sync on the timeline. The way I have got round it, in my case, is by putting the video clip into a compound clip, and then retiming the compound clip.

I'd suggest you give that a go and see if it make a difference, but I'm curious to know, what framerate are you recording the video in?

Good luck.

Seamusvfx wrote: but I'm curious to know, what framerate are you recording the video in?

I'm not absolutely sure what my recording frame rate is! The recording settings on my camcorder offer three categories of recording: "1080/60i" , "1080/60p" , and" IFrame". I've selected the "108060p" setting since this is supposed to be the best possible video resolution from the camcorder. So, according to the settings in the camcorder itself I am recording 60fps. But the "Project Properties" panel in FCPX shows a frame rate of 59.94fps. Could this be the cause of the dys-synchrony? I want my final output to be 960 x 540 at either 30fps (or 29.97fps?) for upload to Vimeo.

Audio won't be effected by "frame rate", but by "sample rate" only. What is the sample rate your camera is set to record at?

You've made life unnecessarily difficult there by recording out of your delivery framerate, unless you a specific reason for wanting to shoot slow motion? Are you sure it was 1080p60 or was it 1080i60?

But on to the actual question, I got a very good answer on this from another user as to why h264 may go out of sync over a long period of time (AVCHD is a derivative of h264). Here's the link to that response:

www.fcp.co/forum/4-final-cut-pro-x-fcpx/...ial-export-bug#29447

Although this makes perfect sense, in practice it didn't actually solve my problem. What seemed to work for me finally actually was making cuts in the timeline. Not changing the edit, just adding cuts with the blade tool every 2 minutes or so along the timeline. My rational (and I'm not sure if it was good rational) was to give the encoder reference points. This seemed to work for me.

Let me know how you get on.

BenB wrote: What is the sample rate your camera is set to record at?

Under the "Record Setup" of my Panasonic HCX920 there is no provision for setting "sample rate".
The only settings are for:
Four versions of "1080/60i": ( {PHI}/ {HA}/ {HG}/ {HE} )
One version of 1080/60p
A setting for "iFrame"
Two settings for 3D recording.
I have selected the 1080/60p setting since the manual states this is the highest quality recording. Perhaps I should try one of the 1080/60i settings?

I thought sample rate only referred to audio recordings. I am not recording audio in the camcorder.
My problem is that audio recorded with Audacity (and with Sound Studio as well) progressively loses synch with the video frames over time.

Seamusvfx wrote: You've made life unnecessarily difficult there by recording out of your delivery framerate, unless you a specific reason for wanting to shoot slow motion? Are you sure it was 1080p60 or was it 1080i60?

By "delivery framerate" I assume you mean my final output framerate. I am trying to ouput video for upload to Vimeo which requires video framerate to be "30 fps (or 29.97)". I see no way on my camcorder to record at any framerate other than "1080/60i" and "1080/60p". When I import the video into FCPX it shows a framerate of 59.94 in project properties.

Seamusvfx wrote: But on to the actual question, I got a very good answer on this from another user as to why h264 may go out of sync over a long period of time (AVCHD is a derivative of h264). Here's the link to that response:

www.fcp.co/forum/4-final-cut-pro-x-fcpx/...ial-export-bug#29447

The link you provided is very good and I suspect that it refers to my problem. I just don't have enough knowledge to fully understand it all.

Seamusvfx wrote: Although this makes perfect sense, in practice it didn't actually solve my problem. What seemed to work for me finally actually was making cuts in the timeline. Not changing the edit, just adding cuts with the blade tool every 2 minutes or so along the timeline. My rational (and I'm not sure if it was good rational) was to give the encoder reference points. This seemed to work for me.

Out of frustration and without any other solutions available to me, I have been doing the same thing that you mention. I skim along the timeline until the dys-synchrony just begins to become noticeable and I cut out a small snippet of audio every couple of minutes to bring it back into synch.