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Old March 6th, 2011, 02:43 PM   #1
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Preventing lost frames upon import with long recordings

I've owned my HD7 for a couple of years and have just run into a curious problem, that being the loss of a few frames of video when recording for a long period of time.
Most of the events I shoot are actually over within a short amount of time or the length of time I need is rather short. I recently shot an event requiring the camera to record continuously for an hour and twenty minutes.

I recorded the event with three cameras: two HD7 and one HD1 (all JVC). Because he HD1 only records HD at 720p, I set the HD7's to record at 1440CBR. My reasoning was because the HD1 records to tape at a constant bit rate recording a constant bit rate with the HD7's might make the importing process less complicated for me.

Upon import all three cameras limit the time length of a video clip to some degree. The HD7's clip length is consistently 19 minutes and some seconds. The HD1 varies, but never over 20 minutes for a single video clip. It could be the NLE that does the time limiting, I don't really know. I have long known importing digital video has time limits for a single video clip. What I didn't realize, or perhaps forgot, is that some video frames are lost upon the creation of a new video clip. That is a big problem when the lost video contains a few very key words of conversation!

My puzzle is how to get around this problem.

The HD1's HD video signal is only recognized by Final Cut Studio, can only be downloaded via Firewire (IEEE1394) and that as a non-controllable device. The HD7's can download via Firewire and USB.

The HD1 was downloaded first as HDV 720p with ProRes codec. The HD7's were downloaded via USB, also to HDV 720p with ProRes codec. One HD7 used MPEG StreamClip to manage the file conversion. The other HD7 used Toast Titanium Pro to manage the file conversion. Both worked flawlessly.

My thought is to change the HD7's recording method to SD, which is 1440 variable bit rate. This is supposed to allow the camera to record for a longer period of time. I am hoping it will either increase the individual clip limits or eliminate the lost frames.

Opinions are welcome.
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Old March 7th, 2011, 12:51 PM   #2
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Re: Preventing lost frames upon import with long recordings

In a test with my HD7, I recorded 22 minutes of full HD-video (1080i/25). It was automatically split into two clips in the camcorder. I imported them into Avid Liquid 7.2, which allows import without any preprocessing. The two clips came in with consecutive time code, the first clips ended at a timecode xxxx:24:00, while the second part started with timecode xxxx:24:01. No frame was missing.
Joachim

Last edited by Joachim Claus; March 8th, 2011 at 03:47 AM.
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Old March 8th, 2011, 02:16 AM   #3
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Re: Preventing lost frames upon import with long recordings

Quote:
Originally Posted by Joachim Claus View Post
In a test with my HD7, I recorded 22 minutes of full HD-video (1080i/25). It was automatically split into two clips in the camcorder. I imported them into Avid Liquid 7.2, which allows import without any preprocessing. The two clips came in with consecutive time code, the first clips ended at a timecode xxxx:24:00, whice the second part started with timecode xxxx:24:01. No frame was missing.
Joachim
JVC HD7 use FAT32 Hard Disk Drive so single file can not be bigger that 4GB. So it actually divides longer clip in to two part.

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Old March 8th, 2011, 04:27 AM   #4
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Re: Preventing lost frames upon import with long recordings

Yes, the 4GB limit is due to the FAT32 format. However, the files are already split at about 18:30 minutes, or about 3.6 GB.
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Old March 10th, 2011, 06:03 PM   #5
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Re: Preventing lost frames upon import with long recordings

Quote:
Originally Posted by Joachim Claus View Post
In a test with my HD7, I recorded 22 minutes of full HD-video (1080i/25). It was automatically split into two clips in the camcorder. I imported them into Avid Liquid 7.2, which allows import without any preprocessing. The two clips came in with consecutive time code, the first clips ended at a timecode xxxx:24:00, while the second part started with timecode xxxx:24:01. No frame was missing.
Joachim
I haven' been able to do a test yet as I have been too busy editing. Perhaps this weekend. I'll do a test recording 30 min. first with the camera set to record in SD mode then follow with camera set to record 1080i/30. Will post the results.
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Old September 19th, 2012, 10:01 AM   #6
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Re: Preventing lost frames upon import with long recordings

Well, after eighteen months of fairly regular use recording long events I can say that anytime the file limit of 4GB is reached there is an 18 frame gap between video files on the time lines of Final Cut Pro 7, iMovie, and Adobe Premiere Elements. Conversion of .tod files for the Apple products was done with MPEG Streamclip and another utility called Clipwrap. Adobe Premiere Elements manages .tod files without the need for conversion.

My solution has been to shoot with two HD7 cameras. One is put into record mode about fifteen seconds before the other.
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Old October 7th, 2012, 06:16 PM   #7
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Re: Preventing lost frames upon import with long recordings

This sounds like a very common problem people run into when improperly importing AVCHD footage.

People browse to the directory on the camcorders memory card where the MTS files are located, copy them to where they want them on their computers hard drive, and then load them onto their video editors timeline, butting the sequential files up against other. Only to find at each junction they have missing frames and/or sound. You are by no means the first to discover this.

The problem is the first file chunk has the normal file header for that type of file. The subsequent file chunks do not, they just have video+audio. You end up with missing frames because the editor is skipping over the header that should be there at the head of each file, but isn't. So it ends up auto-skipping over your missing frames.

I hope that explanation is clear.

I am betting you are having exactly the same problem, even if the file types/extensions are different.

In the case of AVCHD what normally works is to cocatenate all the files in a continuous event into one file upon import.

To do what needs to be done, in a Windows command box this would be:

COPY /B sourceFile1 [+ sourceFile2 [+ ...]] outputFile

On a Mac, which is a form of Unix (Darwin, derived from BSD), the equivalent would be

cat sourceFile1 [sourceFile2 [ ...]] > outputFile

The sourceFiles are of course on your camcorders memory card, the outputFile somewhere on your computers hard drive, with a file system that supports files greater than 4 GB in size.

Try it, hope it works, no guarantees. But if it works you will get to use your second cameras for something a bit more useful :-)
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Old February 1st, 2013, 05:46 PM   #8
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Re: Preventing lost frames upon import with long recordings

Bill Koehler, just want to thank you for COPY /B method ! It save me missing moments in audio when I importing consecutive clips directly in Premiere Pro. Thank You man!
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