FCPX to PT10 - 1ms gap between certain clips

Hi Sam,

This is what the developers said:

If we knew that all audio was at the same sample rate, then we probably could adjust the resolution to the audio sample rather than to milliseconds. However, since it is possible to mix audio sample rates within FCP X, rounding to an arbitrary sample rate does not guarantee no gaps.

We believe that there is a possibility of a very slight loss of audio synchronisation, always less than 1ms. Again, changing the resolution to the sample rather than 1ms would help but not completely eliminate this. To put this in context, a 1ms slip in audio is roughly equivalent to leaning forwards a bit while watching TV (e.g. getting yourself 1 foot / 30 cm closer to the TV).

We could consider improving the resolution for the next release although I am not aware of any other requests for this.

Just to confirm that the statement about sitting closer to the TV was correct, I double checked the maths and it was quite right: Speed of sound in air is 343.2m/s , or 34.32cm/ms.

Thanks Graeme,

Let me know what they say. I'm just about to start editing a feature film on FCPX and the functionality of X2Pro is going to be a key factor in the workflow. If your developers are able to tweak these things then I believe FCPX and X2Pro combined can make editing long form, multi-channel projects very doable.

To reiterate the 'frame line' thing, if I were to send an AAF like this to an audio editor and they opened it up to see that the audio cuts weren't coming on the frame lines but a few samples either side, I think they'd find it a bit disconcerting.

If rounding to a single sample fixes this, then great.

Keep me updated.

Thanks again,

Sam

Sam,

I've asked the developers what they can do and whether it's possible for them to round to a single sample. I'll let you know what they say.

I don't think this should cause a loss of sync. You may be able to tell by importing a video (exported from FCP X) into your Pro Tools session and comparing the waveforms.

Hi Graeme,

Thanks for your quick reply.

I've just looked in a FCPXML and I see what you mean. Why is it that they use fractions then?

Is it possible for you to adjust things to round to the nearest sample instead? Samples are obviously the smallest measurable unit when it comes to audio.

Please find attached the FCPXML that exhibits the problem.

I'm seeing it occur in Pro Tools at (rounded to the nearest frame):

00:00:09:15
00:00:15:00
00:00:17:20
00:00:26:05
00:00:53:14
and more after that...

Interestingly looking at how these edits are imported, I would have expected the edits to be coming bang on the frame lines in PT (seeing as the audio and video are cut together on frame lines). However, they're coming a varying amount of samples before the frame lines.

Is this causing (a very very small) loss of sync?

Let me know what you think.

Thanks,

Sam

Hi Sam,

When FCP X describes clips in the FCPXML, it uses fractions rather than decimals, but when X2Pro creates the AAFs, it has to use decimals. When X2Pro converts the fractions to decimals, it rounds to the nearest ms, so this is probably why there are 1ms gaps.

If this is a problem, we might be able to modify this behaviour. If you would like us to look into it, please attach an FCPXML that exhibits this problem and provide a timecode, or a few timecodes in your project for us to look at.

Hello,

I'm just trying out X2Pro for the first time and I've exported a simple timeline from FCPX as a test.

It has some dialog tracks and a music track, with appropriate roles. 48000KHz, 24fps. ProRes files. Clips on timeline are all 'synchronized clips'.

The aaf from X2Pro imports into Pro Tools 10 absolutely fine, however between certain clips there are 1ms gaps. Exactly 1ms, 48000 samples.

Where the gaps occur seems to be completely at random.

Any thoughts as to shy this might be would be much appreciated.

Thank you,

Sam