Am I understanding HDV editing correctly?

[Steve Grisetti]

Thanks to the panel of expertise for some elementary education -- but I'm beginning to realize I don't know as much as I thought I knew about HDV editing.

I've been reading up on it. Can somebody tell me if I've got this right?

1) You don't want to edit the m2t transport streams that download directly from your camcorder. They're too big and bulky and, even if you've got a powerful enough computer, the files simply don't edit well.

2) Ideally, you could download the m2t streams and your software would convert them to an intermediary codec (Cineform or Aspect DV, for instance) which you can easily edit and, when you're done, output as excellent HDV as your software converts it back into m2t streams. Have I got that right so far?

3) The best results can be achieved by down-sampling in your camcorder and capturing over FireWire. The results will be in this intermediary codec, with excellent quality. The files can be easily edited on any decently powered computer. Then, when you're done -- and this is what I'm not quite clear on -- you output HDV or a BluRay DVD from them? Is that right?

If I'm understanding this right, then downsampling is always the smartest way to go, right? The output is still hi-def video and the quality, even after the conversion, is as clean as the original. Right?

Thanks, guys. I knew I could count on you.

[Paul LS]

Hi Steve, a few comments on your points...

1/ You can edit .m2t transport streams. They are virtually the same size as program streams but carry extra data in the overhead. PE3 can import and edit .m2t transport streams. Basically HDV video is just MPEG2 files. You face the same issues as when editing standard definition MPEG.

2/ You can convert to an intermediate codec such as an AVI and it will be easier to edit than the .m2t file. The issue is that the HDV mpeg is a long GOP (group of pictures) MPEG compared to standard definition MPEG and your processor needs to have enough power to be able to handle and manipulate the long GOP structure. Another advantage of converting to an intermediate AVI codec is that you can export multiple times with little impact on quality like DV-AVI. However, converting to the intermediate codec and then converting back to MPEG will lose quality. It is better to work exclusively in .m2t or .mpg and use smart rendering on export. Sony Vegas used the Cineform AVI codec for HDV, in the latest release they have introduced smart-rendering and so there is no advantage to converting to an intermediate codec if your machine is powerfull enough.

3/ If you want your final output to be standard definition then you need to convert to standard definition at some stage. The issue is PE3 (and 4 I guess) does not do a good job of this downconversion. Other products can do a better job, although more expensive... if you are using PE3 or CS3 you get better results by downconverting in the camcorder to SD rather than converting with PE3/CS3. You will then be editing standard DV-AVI... so no processor power issues either.
If you want your final output to be high definition then you need to capture as HDV (again over firewire) as MPEG2. Then for best quality you need to maintain an MPEG work flow during editing and use smart-rendering for export.

When you use an intermediate codec it needs to be converted back to MPEG for final delivery.

You can also use proxy editing, Ulead VideoStudio and Movie Edit Pro has the option to use this on older machines. The HDV is converted to AVI and editing is done on this. Then on export the AVI is replaced by the actually HDV file and it is edited and exported.

The newer AVCHD format used on most comsumer high definition cameras is even more of a headache to work with. It is a highly compressed mpeg4 variant (15Mb/s compared to 25Mb/s for HDV). Even with my quad-core machine you can not get full frame rate playback from the timeline in Sony Vegas... except when using "Preview" quality... and that is with Vegas using all four cores.

[Steve Grisetti]

That was extremely helpful, Paul. Thank you!

So for HDV editing, you should capture the MPG2 stream directly over FireWire from the camcorder? And Premiere Elements and a 3.0 ghz Pentium have enough power to work with that?

[Paul LS]

Yes, PE can capture HDV MPEG2 over firewire and you can edit with a 3ghz Pentium... infact the workflow is a little smoother than working with standard MPEG as PE handles the HDV natively... no red line above it, no need for rendering. Obviously the faster the processor or using dual-core processors gives a more "smooth" playback in the timeline.

You have limited options with Premiere Elements as it does not offer an "intermediate" or "proxy" editing. You could create an intermediate AVI file say by exporting the timeline as a high definition resolution MJPEG and replace the HDV MPEG2 on the timeline and edit this. Then finally export as HDV MPEG2. This would give you the option of muliple exports without losing quality and may be easier to edit on a slower processor.

[Steve Grisetti]

The best explanation I've ever had, Paul. Thank you very much!

[RJ Johnston]

In Premiere Elements 4.0 HD projects, such as the 720p, you can export the timeline to native MPEG I-frame only format by going File > Export > Movie and then clicking OK. I didn't know about that. In fact if you click the "settings" button, you won't find any options for MPEG. If you put the exported file on the timeline, there won't be any red or green lines above the clip. If you export that by going File > Export > Movie > Ok, You get an identical file. I did a file compare. There was no difference in the files. If you make a change to only part of the clip, only the part that's changed will be recoded when you export again.

When you render a preview, the preview file is an I-frame only MPEG file. That won't be recoded when you export, although it has to be muxed with the audio.

So if you capture to this I-frame only format, and there is no red or green line above it on the timeline, you should be able export it with only the edits getting recoded when you go File > Export > Movie > OK. There's a description of the I-Frame-only format just below where you can change the name of the file.

Is that your understanding?

[Paul LS]

Not sure Robert... when you put an I-frame only clip back on the timeline and export it renders every frame. I would have thought it would have done a frame copy. Infact if you adust the opacity and export it takes virtually the same time as a simple I-frame only export. But having said that I exported-imported-exported a clip 20 times and I could not see any degradation in the clip.

[RJ Johnston]

You can save yourself a lot of time testing by using the DOS FC command to compare two files byte for byte. That's how I discovered that the bytes are exactly the same.

>FC /b video1.mpeg video2.mpeg > compared.txt

[Paul LS]

Hi Robert I am not getting the same result as you when using the DOS FC command. When I export using I-frames only, then re-import and export again using I-frames only there are differences. If I compare the same file (just rename it) then it reports no differences. Repeated it a few times with the same result.

[RJ Johnston]

Did you compare the first generation to the 2nd generation, or the 2nd generation to the 3rd? There will be differences in the beginning because the first time the video and audio get muxed. Try comparing the 3rd generation to the 4th generation.

[Paul LS]

Yes I tested up to 5th generation and they were different with each generation.

[RJ Johnston]

Then I will have to do it over again to see if I get the same results as before, and also list the exact steps I took. When you exported you just went File > Export > Movie and then gave a new file name and saved? No edits?

[Paul LS]

Yes, File>Export>Movie... it showed the, mpeg extension on the file name... I just renamed it and exported. Brought it back in and exported again.

[RJ Johnston]

Thanks Paul. One more thing that crossed my mind, which version of PE are you using? I also wondering if PAL and NTSC might be different.

[RJ Johnston]

Okay. I give up. I can't repeat it. Thanks for checking my results, Paul.

In addition, after I exported to a different format, I couldn't find a way to export to I-frame only again (CompilerMpegProxy), although I think you can set it up in advanced MPEG settings through Share.