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View Full Version : MPEG-2 Editing with VT[2] ... well, sorta



irfan
04-16-2003, 02:57 PM
Dear Friends:

I thought I'd share this with you all. Nothing novel here but it took me a while to set this all up and experiment so I thought I'd share this with you. I'd welcome modifications to this technique to reduce running time. With VT[3], I'll be able to skip one huge costly step(*).

What I needed to do was to take some PAL DVDs (from our archive) and convert them to NTSC while also doing some clipping (and optionally some audio levels adjustment and occasional colour correction).

I experimeted with TMPGEnc to do the PAL->NTSC without too many conversion steps (and hence "generational loss"). But, I wasn't too happy with the results I got. I wasn't getting very smooth motion. The next best thing would have been Canopus' Procoder which is advertised to do PAL <--> NTSC transcoding but that solution costs ~$600. I still might give that a shot for it's batch encoding functionality.

Of course, I could have used AviSynth with funky scripts to do the conversion for me and the adjustment of framerates with the corresponding audio length tweaks in BeSweet. I looked into that but I needed something done quick and it was taking a long time to figure out how to setup my script correctly.

That's when I decided to go on a frameserving journey with VT[2]. So, I took the original PAL .VOB files from the archive DVD and used DVD2AVI to open it. I set the Audio-->Output mode to be .WAV. Modified the Colour Space to YUV 4:2:2 and changed to TV Scale. Then I saved the DVD2AVI project (.D2V). This process took <10 minutes for a 2 hour DVD and produced a .WAV file to use later.

I then proceeded to open the .D2V project in VFAPI which setup a frameserver and gave me a wrapper .AVI file. This took <1 minute.

Finally, I opened VT[2] and Ted and loaded up the .AVI file onto the timeline. I fitted the previously produced .WAV file underneath the video. Note that lip sync was out so I had to move the audios start offset to -00:00:01:00. I'm still trying to figure out where that came from and how to fix it. Anyway, I did all the editing I had to do (mostly clipping and audio level adjustment) and saved the files as a real AVI file. This took ~<2x realtime. Aweful aweful slow :( . VT playback from timeline of frameserved .AVI also drops frames.

Finally, I loaded TMPGEnc and encoded this AVI file back out as an MPEG stream to be loaded into DVD Studio Pro. Done.

(*) With T[3], hopefully we can skip the saving out the file from VT only to then load it again in TMPGEnc. Hopefully T[3] will allow proper frameserving.

Big hack is how I like to think of it. However, the resulting NTSC quality was pretty good and I got a chance clean things up.

Now, please tell me how to optimize this process. Anyone have needs similar to this? I imagine that people must have to deal with files ripped from a DVD. Was this useful? Am I smoking crack?

Irfan

kleima
04-17-2003, 09:24 PM
Just capture the thing from the DVD, uncompressed in real time on the T[2], via Y/C. When you are done with your tweaks re-encode in TMPGenc. Someone out there has a plugin that make TMPGenc recognized uncompressed RTV files.
The Toaster handles the PAL/NTSC stuff automatically in real-time.

irfan
04-17-2003, 11:12 PM
I'd like to stay digital, though.

Your point is well taken. My exercise may look useless to you but I'm trying to setup a process by which staffers will do several hundred archived DVDs from our station over the next few months.

kleima
04-17-2003, 11:51 PM
Staying digital means nothing unless it is all uncompressed. You can degrade a digital signal faster than an analog one with compression. (Even 'lighter' compressions like DV. MPEG for DVD's is a heavy compression.) You're not going to lose anything going from the DVD to the Toaster with Y/C even though it is analog. And, either way you want to go back to DVD. That is where you will lose, but that step is the same for both scenarios.

bbeanan
04-18-2003, 08:49 AM
I would have to agree about just using a DVD player and capturing the footage as an RTV

I just finished a project where my client had their source material on DVD, which I captured via componut toaster inputs. It was fast and worked great...

Granted I did do another project where all I had my my base system on site at a tradeshow and one of my clients source DVDs turned out to be PAL and I did not have a PAL deck with me so I did the convertion using TMPEGNC.

irfan
04-18-2003, 01:07 PM
OK, I think I understand your arguments. I agree that given my source material, I shouldn't expect much better staying in digital rather than going out to analog.

However, I don't buy the argument that staying digital will be worse. If I'm out of line, please educate me.

What I'm doing is tantamount to pulling each frame from the DVD through a frameserver into VT[2] which then converts this into PAL and saves out to a file. Now, suppose I save out to RTV at this stage. Why is that going to result in worse quality than having captured to RTV in the first place.

The only thing that I can come up with is the quality of the decoder (dvd2avi et al. vs. a PAL dvd player).

In the end, the decision comes down to efficiency. And it turns out that with VT[2], the time efficiency of using my method versus yours is similar. (1x realtime to capture, 1x realtime to render out my edited rtv, assume Tx realtime to encode VERSUS <1/2x realtime to rip, 1 1/2x realtime to render out to rtv, Tx realtime to encode). With VT[3], we'll end up with 1/2x realtime to rip followed by (T+e)x realtime to render/encode, where, I expect, e is smaller than 1. (I think I might have just gone off the deep end).

Note that my method, with VT[3], will require less interactive control than the alternate. Also, the ripping can be done on a machine that is not the VT machine.

Kurt_Henning
04-18-2003, 02:32 PM
I ahve done what you are doing the long way using tmpgen.

However, since the t2 will allow you to run a DVD through the S-in or SDI, it looks great.

I had to take a bunch of cuts off a DVD. I tried ripping (even though it was the clients actual product)DVD2avi and several other solutions.

None of them looked as good as digitizing the DVD into the toaster 2.

YMMV

I think this whole thing boils down to time.

If you ahve until tomorrow and don't mind waiting -- use tmpgen

If you ahve to get the edit out the door today -- digitize