Simple HDV cut-editing back to tape w/o re-rendering - is this possible? at DVinfo.net

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Old June 4th, 2007, 11:14 PM   #1
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Simple HDV cut-editing back to tape w/o re-rendering - is this possible?

Hi all,

My question is simple: is it possible for me to capture HDV from a raw tape with like 50 takes of different clips, and then just output a selected few keepers back to tape, without incurring any re-rendering of HDV?

I used HDVSplit to capture HDV with scene detection, and then simply put the good takes into the Premiere Pro 2 timeline. I would like to output this timeline in its original form (without re-rendering) back to HDV tape for source archive (therefore I don't need to keep the bad takes.) I have done things like this in the miniDV editing project all the time. In HDV, however, PPro will always try to render it before output back to tape.

Does the long GOP MP2 encoding in HDV prevent this from happening like in miniDV world? If so, is there some workaround for this (by using some other tool)? Thanks for your advice!

Paul
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Old June 5th, 2007, 06:14 AM   #2
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I use Avid so I'm sure things are a bit different but..

Avid edits native HDV. I use hard disk recorders now (no tape) and instead of downloading them as a huge chunk and clogging up my hard drives with stuff I'll never use, I scan through the drives and put the pieces I want to keep in a timeline then use the "FUSE with import" function in Avid to bring the footage into my media library. I end up with a single file from a recorder with a string of cuts only transitions and save a ton of drive space. This is a very fast process.

The entire file does not have to be rendered only the areas around the cuts to rebuild the GOP frames and make everything come out correctly. If you were to do all your cuts on I frames no rendering should be required.

It will only work this way if your setup is also doing native HDV and not using an intermediate CODEC.

Do you know if you have your timeline setup to use a native HDV codec? I'm afraid I have no experience with Premiere.
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Old June 5th, 2007, 05:33 PM   #3
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What you did was exactly what I tried to achieve, just without the tapes. I did the same thing in PPro2 (using PPro's HDV preset with no intermediate codec) but was not sure if PPro2 simply just output the files like Avid did. It took a really long delay in the "render and export" dialog before the m2t data started streaming to the camcorder...

I know there are tools to cut m2t files in an "I-frame accurate" way. Are there tools (hopefully free) to export the m2t files back to tape via Firewire?

Paul
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Old June 5th, 2007, 06:41 PM   #4
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My understanding with the way things work with camera captures is that material is off load to a file format that is editable, then when it goes back to camera, it has to be converted to the true HDV format again. That is why there is a delay for reencoding in Premiere when you go back to tape.
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Old June 5th, 2007, 06:49 PM   #5
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Quote:
Originally Posted by Po-Wen Shih View Post
...is it possible for me to capture HDV from a raw tape with like 50 takes of different clips, and then just output a selected few keepers back to tape, without incurring any re-rendering of HDV?
I think you could do this using Edius by capturing in HDV format with scene detection, which generates separate M2T files for each clip, then write the files you want back to the camera using the "MPEG TS Writer" utility. No editing or rendering required if you don't need to trim the clips.
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Old June 6th, 2007, 11:44 PM   #6
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I did a quick experiment (my earlier project took too long to export) in PPro 2:

1. Capture a short, single scene m2t clip (~20 sec) via HDVSplit (original)
2. Import into PPro timeline. I can see it has two P frame before the first I frame at the beginning.
3. Export the clip untouched to tape (export 1) - taking ~1 min to transcode before export
4. Export the clip with the first two P frame trimmed in PPro timeline (export 2) - take ~1min to transcode before export
5. Use HDVSplit to capture export 1 and 2 back
6. Put all three clips into PPro timeline, sync up the frames
7. Frame-stepping the three clips to compare the quality

What I have observed:
A. Both export 1 and 2 are much worse than original - much more noises - indicating both have been re-compressed under HDV codec again. You can see the noise during video playback and much more so when stepping through the frames.
B. Both exports are missing the first 3 to 4 seconds of the original clip

This confirmed Chris's understanding and what I have been suspecting: PPro has to transcode m2t (not just read the m2t and output the packet stream) before it exports. There is no simple "m2t writer" in PPro 2 to output the data stream untouched.

Kevin,

I checked on Canopus site on their "MPEG TS Writer" and found an interesting info: (http://www.canopus.com/canopus/techn...usworkflow.php)

"Write back to the HDV camera — The MPEG TS Writer built into EDIUS may be used to write projects back to the HDV camera. MPEG TS Writer is specifically designed to write an HDV-compliant MPEG-2 Transport Stream created from ProCoder Express for EDIUS back to an HDV camcorder or deck. It is important to understand this process, as many SD editors who have become accustomed to realtime editing may not realize that there will be this ‘extra’ step to output back to the HDV camera. Currently no solution provides realtime HDV output directly from the timeline."

It sounds to me Edius is using an intermediate codec to handle m2t... I am not sure if this means that Edius is also doing the same thing like PPro 2 - the Mpeg TS Writer still need to do the extra "tarnscoding" step before it can export. Have you done a quick test to see if the export clip contains the same quality as the original one?

Well, I would think after several years of existence, HDV would be well supported by all NLEs by now. I would never expect to have such a hard time just trying to do a simple thing like this. Or maybe my understanding of the HDV workflow (no one ever wants to save the original HDV clips back to tape??) or how m2t export works is really off the mark?
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Old June 6th, 2007, 11:54 PM   #7
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BTW, I forgot to mention one side effect from PPro 2 export:

After capturing the two exports back as two individual clips, I used HDVSplit's "scene split" feature to process the two clips in order to get rid of some unwanted video at the beginning. To my surprise, both clips were divided into many "scene" clips - each scene is around 1 sec (size around 1-2MB per scene.) I tried the same process on the original and it came out as one clip (since this was from a continuous shooting without pause/stop.) I am not sure if this means something PPro 2 screw up or not.
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Old June 7th, 2007, 09:03 AM   #8
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Quote:
Originally Posted by Po-Wen Shih View Post
It sounds to me Edius is using an intermediate codec to handle m2t... I am not sure if this means that Edius is also doing the same thing like PPro 2 - the Mpeg TS Writer still need to do the extra "tarnscoding" step before it can export. Have you done a quick test to see if the export clip contains the same quality as the original one?
Edius offers both an intermediate HD codec and native HDV editing, but that's not what matters here. What I'm saying is that as soon as you finish capturing HDV clips with scene detection you should be able to write the individual M2T files that generates back to the camera using the TS Writer utility. I haven't specifically tested this to confirm it works without modifying the clips, but that should be the case. I can tell you that rendered HDV projects written back to the camera from Edius look pretty good, so unmodified clips should look fine.
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Old June 19th, 2007, 10:41 AM   #9
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Quote:
Originally Posted by Po-Wen Shih View Post
BTW, I forgot to mention one side effect from PPro 2 export:

After capturing the two exports back as two individual clips, I used HDVSplit's "scene split" feature to process the two clips in order to get rid of some unwanted video at the beginning. To my surprise, both clips were divided into many "scene" clips - each scene is around 1 sec (size around 1-2MB per scene.) I tried the same process on the original and it came out as one clip (since this was from a continuous shooting without pause/stop.) I am not sure if this means something PPro 2 screw up or not.
It sounds to me as though the clips created by PPro2 do not have a time-stamp that HDVSplit can recognise. I have seen something very similar when capturing DV footage using Scenalyzer: footage shot on my Canon MVX350 before I had set the date and time was split into 1-second chunks. Scenalyzer looks for jumps in the date and time to spot scene changes, and I guess HDVSplit does the same kind of thing.

HTH
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Old July 17th, 2007, 08:18 AM   #10
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I moved from DV and make first steps in HDV (Canon HV20).
Use HDVSplit to capture scenes and Canopus MPEG TS Writer to export selected good scenes back to tape for archiving. Original datecode preserved- it's good, but...

When exported sequential clips, then later playback from tape is OK, but if any scene (bad shoot) is omitted, then in this point picture freezes for about half of second.
I can't understand why.

Where the reason? GOP structure? Timestamp difference?
Any idea, please.

AK
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