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-   -   Long GOP m2t files structure. (https://www.dvinfo.net/forum/high-definition-video-editing-solutions/58356-long-gop-m2t-files-structure.html)

Alex Moss January 15th, 2006 04:48 PM

Long GOP m2t files structure.
 
I have a question.

A client of mine wants me to edit a 720p video for him. Besides my internal wrestle over going Premiere or Vegas to edit it on, (There will be a lot of colour correction. Any suggestions?), I have another question I am having trouble finding an answer for.

Being 720p, my system can essentailly edit the raw m2t files with little to no hiccups, or slow down. Great! I would have thought. But there seems to be some buzz about the m2t files having long GOP files, and therefore being not totally suitable to edit in.

This in mind, should I be using an intermediary codec such as Cineform, EVEN THOUGH, I can edit natively?

If so, why? And continuing on from this then, will Cineform, or Gripshift be the most lossless in terms of output and quality maintenance.

Believe me I have used the search command until my girlfriend was screaming at me, so it's time to draw on your clever expertise my fellow HDV enthusiasts.

John Rofrano January 16th, 2006 12:53 AM

If you are doing a lot of color correction you definitely donít want to edit the M2T file. Why? Because each frame is not a full image as is the case with DV (hence the long GOP). For example, the MPEG2 GOP for the Sony Z1 and FX1 is made up of a group of 15 frame sequences. Only one frame in the 15 (I-Frame) contains an entire image. The other 14 frames (B-Frames and P-Frames) contain delta and predictive data only. This means that color correcting on these 14 delta frames is not recommended since the frames donít actually exist (they are composed of the I-Frame and B & P-Frames combined). Do you really want to color correct frames that donít exist? It is much better to edit in an AVI format like the CineForm intermediary file and GearShift can make these files for you.

~jr

Steve Crisdale January 16th, 2006 01:37 AM

As John has already said, working on the raw m2t files isn't going to give the best end result.

Further to John's GOP explaination, there's the fact that m2t files are actually MPEG2 transport streams. This means they are already compressed.

If you work with still images you will know what happens if you do something to a JPEG and save it as a JPEG... in case you don't, the re-rendered and re-compressed JPEG gets even worse artifacting, because you're compressing compression - if you see what I'm on about.

MPEG is just glorified JPEG, so the same principle applies. Keep to as uncompressed as you can when working on the "master" clips.

Cineform CFHD is the best offering on PC to give you that "uncompressed" master footage to work with. If you go Premiere Pro, then get AspectHD. If you go Vegas (my preference having worked in both) get ConnectHD and/or Gearshift. ConnectHD gives you the HDLink capture utility with the various frame rate variables and the quality options. Gearshift is a script plug-in for Vegas that provides similar frame rate variables as well as the ability to work with proxies for the HDV originals if you prefer to work that way.

Bottom line... If you want an easy to get a grip on, yet powerful and professional NLE that has the best HDV support currently available, go Vegas 6. And do yourself a favour by getting both ConnectHD AND Gearshift.

Now for all the other folks to give you their recommendations...

Alex Moss January 16th, 2006 03:31 AM

Both exceptional and excellent answers.

My analytical nature is unfortunately a double edged sword. While many are happy with simply the knowledge that Cineform is good, I reaaaaally need to know why, and the hows and whos and whys.

Sounds excellent. I think I am left with 1 final question / confirmation to satisfy my research addled brain....

That is...

In fact... stuff my thoughts on what I think I know, I'll just ask.

Assuming I stick with good ol Vegas 6c, then...

Cineform Connect OR Gearshift OR both and if so, why.

Does one perform better / different to the other. Links to the technical understanding are great, but I've always found user experience tells a great story too.

thanks again for your wonderful help.

John Rofrano January 16th, 2006 08:00 AM

Quote:

Originally Posted by Alex Moss
My analytical nature is unfortunately a double edged sword. While many are happy with simply the knowledge that Cineform is good, I reaaaaally need to know why, and the hows and whos and whys.

Alex, Fortunate for you the CineForm guys have an extremely informative web site. You can READ about the CineForm Intermediateô Format on their technology page. You can SEE the difference that CineForm makes on their Quality Analysis page. I urge you to take a look at the later. This will show you why you want to edit intermediate files.

Quote:

Originally Posted by Alex Moss
Cineform Connect OR Gearshift OR both and if so, why.

I wrote GearShift and I use CineForm Connect HD so I will try and give you an unbiased opinion of both (if thatís possible) ;-)

GearShift is $50 and will take the M2T files that youíve captured and convert them into DV Proxies and optionally, CineForm intermediate format (using the CineForm codec thatís included with Vegas 6). With GearShift your workflow is:

1. Capture M2T with Sony capture utility
2. Convert to DV Proxy and/or intermediate/YUV format
3. Edit using Proxies at DV speed
4. Shift Gears to swap the M2T files back in for final render

CineForm costs $200 but it has the ability to capture directly to intermediate AVI format in ďnearĒ real-time. Your workflow is unchanged from capturing DV and this saves you step of capturing M2T then converting (which is double the time). It also has scene detection, and some special options for handling 24p and mini 35 adapters that flip the image. What it doesnít give you is the DV Proxies which are critical if you have slower PC that cannot handle HD.

There are times when Iíll use CineForm and capture directly to AVI for simple projects. But even with my AMD Athon64 X2 4600+ dual core PC, there are times I cannot playback the CineForm intermediate in real-time even in Preview mode! If I were to do a lot of compositing in HD, there is no way I could get even close to smooth playback. For those times, I will use GearShift because the DV Proxies it produces are a lot faster to process and multi-track video compositing isnít a problem.

So depending on the project, I will use one or the other. I urge you to download the trial of both products and try them out for yourself so you can see which workflow works best for you. GearShift is best if you donít have a really fast PC (i.e., less than P4 3.2GHz) because you can still work at DV speed with the proxies. It can also make the CineForm intermediate files and Sony YUV files for going back to HDCAM. CineForm has the best workflow, but you still need a very beefy PC and even then real-time playback is hard to achieve at times.

~jr

Alex Moss January 16th, 2006 06:15 PM

Excellent John. Thankyou very much. All the information was very useful.

The client I am working for has done their pilot in 720p 24fps with a view to doing the series in 1080i pulldown to 24fps using Atlantis I suppose.

With this in mind, I feel I should use Cineform Connect for the pilot, as my PC seems to handle the 720p files ok, and the Gearshift DV proxies for the 1080i, which seem to jutter even after Cineform is applied.

Thanks again for this info. I have asked around, and it seems no-one here in Sunny South East Qld except me is going the way of HDV at this point, so I am using it as a selling point, and all this information is great.

Cheers
Alex

Steve Crisdale January 16th, 2006 07:00 PM

Quote:

Originally Posted by Alex Moss
Excellent John. Thankyou very much. All the information was very useful.

The client I am working for has done their pilot in 720p 24fps with a view to doing the series in 1080i pulldown to 24fps using Atlantis I suppose.

With this in mind, I feel I should use Cineform Connect for the pilot, as my PC seems to handle the 720p files ok, and the Gearshift DV proxies for the 1080i, which seem to jutter even after Cineform is applied.

Thanks again for this info. I have asked around, and it seems no-one here in Sunny South East Qld except me is going the way of HDV at this point, so I am using it as a selling point, and all this information is great.

Cheers
Alex

Crikey!! Another flamin' Aussie!!!!

I thought we were meant to be crass technophobes who aren't as 'into' new technology as more 'advanced' countries...

Must be all this hangin' around upside down down-under (does a double negative like that make a positive?) that makes us brave or stupid enough to use technology folks 'up-top' tell everyone who's gullible enough to listen, "it isn't good enough"...

Yee Haa!! Put another prawn on the barbie... crack a cold one and enjoy all that melanoma makin' sun!!

Alex Moss January 16th, 2006 07:06 PM

Strweth! Good to see us cobber dingo Aussies stepping into the game, eh?

Cheers mate,
Alex

Steve Crisdale January 16th, 2006 07:22 PM

Quote:

Originally Posted by Alex Moss
Strweth! Good to see us cobber dingo Aussies stepping into the game, eh?

Cheers mate,
Alex

Stone the Crows mate!!

Let's put the wind right up all them what don't understand the lingo... then we'll get banned in the best Aussie style tradition!!!

Up the Mighty ANZACS!!!


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