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Help me understand this! m2t, HDV, render time

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Matt2005
Help me understand this! m2t, HDV, render time
on Jul 20, 2007 at 1:09:49 am

I had a 35 minute HDV recording that I captured into XPro v5.2 in a 60iHDV Project and it created a 6.2 GB video file in the MXF folder and wav files in OMFI Folder all in real-time.

Next I wanted to get that "data" back onto another HDV tape (yes, even without matching timecode), just to have another tape in case the original gets damaged.

So I set about to export the entire 35 min masterclip along with some black head & tail Filler. With my timeline highlighted, I chose Export/ HDV / and used the "Best" option. Yeow... this request took 5 hours and 14 mins to complete. Isn't there a faster way to create an m2t file?

What if I just use a freeware program like HDSplit to generate m2t files? They would be made in real time and I suspect that Avid can use any file in the m2t format for export with its HDV to Tape feature.

What's the m2t story? Do editors today just forget about HDV tape clones an simply back-up their MXF & associated Audio Files onto hard drives and DVDs?

Out of curiosity: will FCP be able to import the original Avid MXF file and associated wavs?

Thanks for your help!






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Joe Womble
Re: Help me understand this! m2t, HDV, render time
on Jul 20, 2007 at 3:43:20 am

HDV is an acquisition format. The codec doesn't hold up well to compositing or multiple generations. DNxHD is a mastering codec available in Avid you can use by transcoding your HDV footage. It looks great and does not require "exporting" like HDV.

What are your deliverables? That will determine whether you need the extra step of exporting out to HDV.

Regards,

Joe Womble


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epontius
Re: Help me understand this! m2t, HDV, render time
on Jul 20, 2007 at 4:45:32 am

Think he's just trying to make a dupe of his original tape. Capture to avid then export back out to the deck on another tape... He'd end up having to create a m2t to export back to HDV either way.

Erik


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Matt2005
Re: Help me understand this! m2t, HDV, render time
on Jul 20, 2007 at 12:47:16 pm

Thanks, Joe & Erik- yes, i want to make a backup clone of my raw HDV footage and I thought I could do it to HDV tape. But I'm now learning that there are big differences between DV and HDV tape despite their common cassette size. When DV came on the scene it was also called an "aquisition format" as I recall. However, when a DV tape was captured into Avid and no effects were added, it was said that the firewire output recorded back onto even a cheap firewire camera would be a digital clone (all except for TC). Now with HDV, I *think* that notion is gone and that's what I want to understand better.

My deliverables for completed projects will run the gamut from DNxHD'd transcoded media (destined for a finishing suite with vtrs galore) to SD DVD's made directly from either the Avid XPro firewire or perhaps from an HDV tape used to record it.

But even if I do one of these incredibly long renders on, for example, a one hour program, when I export that m2t file back onto HDV tape it seems it will have taken another quality "hit" despite that long render. Is this correct?

Erik- you are correct. My thought was: "why render for 5 hours if I can just re-capture via firewire with a different tool in order to create an m2t file in real-time" (non-matching TC) especially if that m2t file can be used as an Export file by Avid to export to an HDV tape as a backup? I guess I can try it myself and see if it works. That HDVSplit program is one I'm familiar with.

I'm still interested to know if Avid-created MXFs and associated wav audio is a format that imports into FCP.

Thanks again.


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Matt2005
Re: Help me understand this! m2t, HDV, render time
on Jul 20, 2007 at 4:18:45 pm

"I guess I can try it myself and see if it works. That HDVSplit program is one I'm familiar with."

I just did- "HDV Split" makes an m2t file in realtime that XPro can then "Export to HDV Device" also in realtime back to my HDV Camcorder. I don't see a quality drop, I'll leave that to the experts.


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epontius
Re: Help me understand this! m2t, HDV, render time
on Jul 20, 2007 at 7:37:23 pm

My guess is that Avid "demuxes" the HDV MPEG2 essentially separating the audio and video streams in order to be able to edit it properly...there is probably some other manipulation of it in order to get it into a state it can stuff into MXF.
When you get ready to export this back to tape, it has to re-build a transport stream (M2t) by compressing it again.
Most of the time when working with HDV I capture it HDV and transcode my selects and other good stuff I'll be using to DNxHD 145, which takes up more space, but works a lot better and faster on the timeline and has better interoperability with other apps (ie. After Effects).

If you intend on making clones of your tapes a lot, it might be more time saving (time is money) to buy another deck...hook 'em both up via firewire and clone away in realtime...timecode, CM chip and all. Just did this for some HDV tapes we needed copies of...our HVR-1500 deck even gave step by step directions...

Erik



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Matt2005
Re: Help me understand this! m2t, HDV, render time
on Jul 21, 2007 at 1:14:40 am

"it has to re-build a transport stream (M2t) by compressing it again"

OK Erik- well if we're compressing again to make an Avid-exportable m2t file I'd guess that I'm better off avoiding the m2t-toMXF-to m2t
compression when I can apparently just move the original m2t off the original HDV tape and copy to another. I'm going to take my clone file
from HDVSplit and DNxHD it and try to compare it with the same from the Avid capture that I also DNxHD'd.

I wish I had budget for the Sony HDV vtr, but not likely unless I rent. If I need TC to match, I'm getting used to the idea of copying the Avid MXF + wav captures to DVD. I *think* that preserves my TC, too.

Thanks again for your help.



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