transcoding and loss of sync

[Andrew Young]

I'm going over some workflow options (24p for someone who cant wait for the FCP upgrade and 30p for someone else who has broken timecode that won't capture native) and have run into some snags with the whole transcoding scenario.

The m2t capture is no problem on HDVxDV or DVHSCap, even of whole tapes, but I am loosing sync on the HDVxDV transcodes on takes over about 5 mins (a 25 min clip is a few seconds out at the end).

I thought this was simply due to the fact that HDVxDV transcodes were incorrectly timed at 24 fps rather than 23.98 and I was happy to be able to try Nate's MPEG Streamclip demux method.

Originally Posted by Nate Weaver

I've found though if you demux the m2t to separate m2v and aiffs, then RELOAD those into MPEGSTREAMCLIP, a resulting transcode to DVCPRO HD will be timed at 23.98.

That's a pretty cool trick, Nate – how in the world did you figure that out? Unfortunately, when I tried this (merging the transcoded clip from the demuxed m2v with the aiff file in FCP, after resetting the video speed back to 23.98 in Cinema Tools) it drifted out of sync as well, but in the other direction.

So at present, I'm not having luck with the transcoding approach. And the capture card method is going to give me 60p, which takes up a lot more room and there is no easy way to remove the pulldown. Any one having success with either of these methods on FCP?

[Paolo Ciccone]

Hi Andrew.

Recently I had the same experience, I found out that if I moved the InPoint in HDVxDV a few seconds ahead to trim the beginning, and then exported, the sound is back in sync.
Hope it works for you.

[Andrew Young]

Very interesting Paolo. I will try it. Thanks.

[Rob Stiff]

Take your m2t file captured from HDVXDV and then
bring it into Streamclip. Use the "Fix Timecode Breaks"
option. Then, use the convert to Quicktime options.
pick Apple Intermediate Codec, deselect interlacing boxes
and select 1280x720 (HDTV).

You can then bring the files into FCP.
Make sure your FCP's video sequence preset is modifided to
Apple Intermediate Codec, HDV 24p settings you have to create.

Thank God Streamclip has a fix timecode breaks option.

[Andrew Young]

Originally Posted by Rob Stiff

Take your m2t file captured from HDVXDV and then
bring it into Streamclip. Use the "Fix Timecode Breaks"
option. Then, use the convert to Quicktime options.
pick Apple Intermediate Codec, deselect interlacing boxes
and select 1280x720 (HDTV).

You can then bring the files into FCP.
Make sure your FCP's video sequence preset is modified to
Apple Intermediate Codec, HDV 24p settings you have to create.

Thank God Streamclip has a fix timecode breaks option.

Hi Rob,

Thanks for the reply.

When I use this approach I get clips that have 24p inside a 60p stream, which is not what I want becuase of the space requirements and the difficulty of removing pulldown. Have you been able to use this method to get 24fps clips with no sync drift?

[Rob Stiff]

Yes, method works great.

My suggested approach was aided by Nate Waver.
I see Nate is constantly bombarded with the same topic
over and over on this discussion board.

A ~60 minute m2t file is about 8 gigs. Then
converted into AIC 720 24p (HDTV) Quicktime
is about ~17 Gigs (depending on your original footage's audio settings)

We have smooth realtime editing using multicam FCP with 4 Cameras
with these AIC Converted Quicktimes on a G5.

I don't mess with Compressor or Cinema Tools. I just use HDVXDV and Streamclip to be able to edit this HDV footage in realtime.

I am inerested in finding some low cost HDV or HD decks that can take
and HDMI input and record with better color options then the HD100U
or BR-50U 4:2:0 low standard. But, hey if have you seen some of Nate Waver's footage?; the colors are fantastic! What is his trick? Would make a heck of a writeup in Videography Mag.

[Andrew Young]

Originally Posted by Rob Stiff

Yes, method works great.

Hmmm. Rob, how are you getting 24p clips rather than 24 in 60 with MPEG streamclip? Are you demuxing first as Nate has suggested, and if so is it holding sync over the length of the entire tape when rejoined with the audio? Or have you found another way to avoid the pulldown frames?

HDVxDV is the only way I have been able to get 24p in my transcodes without demuxing, but sync is a big issue. Havn't tried Paolo's method yet..

Thanks for the input.

[Andrew Young]

Originally Posted by Paolo Ciccone

I found out that if I moved the InPoint in HDVxDV a few seconds ahead to trim the beginning, and then exported, the sound is back in sync.

I tried your method, Paolo, but got the same out of sync results. Don't know why. I also tried exporting an AIFF file of the audio from the transcoded clip before changing the frame rate from 24 to 23.98 in CT, and then joining the two back together. The sync was better, but still unacceptable.

Don't know what gives...

[Paolo Ciccone]

Originally Posted by Andrew Young

I tried your method, Paolo, but got the same out of sync results. Don't know why. I also tried exporting an AIFF file of the audio from the transcoded clip before changing the frame rate from 24 to 23.98 in CT, and then joining the two back together. The sync was better, but still unacceptable.

If you play the original .m2t file with VLC or MPEG Streamclip are they out of sync?

[Andrew Young]

Originally Posted by Paolo Ciccone

If you play the original .m2t file with VLC or MPEG Streamclip are they out of sync?

Hi Paolo,

No. Sync is fine on the m2t files when played back on any of the above or HDVxDV. The loss of sync is happening in the transcoding process.

[Paolo Ciccone]

Originally Posted by Andrew Young

No. Sync is fine on the m2t files when played back on any of the above or HDVxDV. The loss of sync is happening in the transcoding process.

Hmmm. Any chance you can put a short clip somewhere where I can download it and try converting it?

You can email me using phciccone at gmail dot com

[Andrew Young]

Thanks very much for the offer, Paolo. I'd welcome some help to figure out what is going on. The only problem is that a short clip isn't going to tell us too much - the drift only becomes obvious after about 8 minutes and that would be a pretty big clip to get to you. At the end of 25 minutes, which is the longest m2t capture I have done, it is about 1 second out. Of course, the m2t files have numerous camera start/stops in them. Maybe that is a factor, but I'm not sure why it should be. So are you able to transcode m2ts of this duration witout any drift?

[Paolo Ciccone]

Originally Posted by Andrew Young

Thanks very much for the offer, Paolo. I'd welcome some help to figure out what is going on. The only problem is that a short clip isn't going to tell us too much - the drift only becomes obvious after about 8 minutes and that would be a pretty big clip to get to you. At the end of 25 minutes, which is the longest m2t capture I have done, it is about 1 second out. Of course, the m2t files have numerous camera start/stops in them. Maybe that is a factor, but I'm not sure why it should be. So are you able to transcode m2ts of this duration witout any drift?

You're very welcome Andy, the least I can do for someone who helped us so much. I'm not sure what can be done but this is one of those things that is quite hard to fix "remotely" so I'd like to give it a try personally and poke around. I can download bit clips, a few hundred megabytes are not a problem. See if you can zip it and shrink it a little bit. Send me a URL via email and I'll try my best :)
I had similar problem with several clips for my Vodcast. The .m2t was fine but the transcoded file was 2 or 3 seconds off. My clips were probably 5-10 minute long.

[Daniel Patton]

Andrew, I was following this thread and was wondering if you or Paolo had anything new to report on your sync issues?

It might be worth duplicating one of the tapes and fed-Xing it to Paolo if you are still having no luck on your end.

[Paolo Ciccone]

Originally Posted by Daniel Patton

Andrew, I was following this thread and was wondering if you or Paolo had anything new to report on your sync issues?

It might be worth duplicating one of the tapes and fed-Xing it to Paolo if you are still having no luck on your end.

Hey Daniel.

I didn't get any news from Andy over the weekend so the jury is still out. If the size of the files is not out of reach I have no problems in letting the download go all night.