Export MPEG-2 without recompression
by Koby Goldberg
on
Jul 4, 2009 at 5:01:40 pm
Sorry for posting again, but I didn't get an answer for the last post, and I think it should be quite simple...
How do I export from PPRO MPEG-2 file, without recompression the whole video again (my source video is also MPEG-2, and I am going to make only small changes to it).
Is it possible in PPRO CS4 or in CS3 ... ?
Re: Export MPEG-2 without recompression by Koby Goldberg on Jul 4, 2009 at 7:17:48 pm
Hi Brian,
Thank you very much for your repoly !
I intend to replace several segments of few seconds each with different footage, and add some transitions. The whole video is about 1 hour, so most of it will stay the same.
Re: Export MPEG-2 without recompression by Brian Louis on Jul 5, 2009 at 11:06:02 pm
Good luck on not recompressing if you are doing transistions and adding other footage, most of the time AFAIK Ppro will recompress Mpeg, if you wanted to add like footage and just do cuts there is software that will do that without recompressing
Re: Export MPEG-2 without recompression by Koby Goldberg on Jul 6, 2009 at 7:53:03 am
Brian,
Thank you for the reply!
I know that for DV compression, PPRO has a feature for not recompressing (some checkmark on the export video options), isn't there any hidden feature similarly for MPEG2... ?
I tried along time ago the MainConcept MPEG plugin for PPRO (for CS2 version), and it did just that: Upon export, it exported fast on any unchanged footage, and then would stop and actualy render slower on any changed/added footage. However the newer versions of MainConcept for CS3/CS4 doesn't do that anymore... they recompress the whole video... That's too shame they took out the best feature of their plugin!
I didn't understand from what you wrote: Is there or is there not another software that can do it ?
Re: Export MPEG-2 without recompression by Tim Kolb on Jul 6, 2009 at 3:17:44 pm
There is no software that can take long-GOP MPEG and do any editing to it without recompression.
These clips are encoded originally as "Groups of Pictures" that are a given number of frames on length...12, 15, 20, etc. The first frame (the 'I' frame) is the only complete frame in the entire group. The rest of the images are derived from the I frame.
When you do even the most rudimentary cuts, you are shifting these groups and cutting pieces of them off.
For an easy example, let's say you lay 2 seconds of 29.97 HDV onto an edit timeline. There would be four 15 frame groups in this clip. For you master edit, you decide you need 10 frames of black, then a 7 frame fade up...simple stuff. Now you want to export back to MPEG2...
However, now the first frame of the first GOP is not the first frame of your video...it's a black frame, and it's 10 frames earlier than you original first GOP I frame...which makes the original first I frame of the clip, frame 10 of the first 15 frame GOP...not to mention that every GOP thereafter is shifted and needs to be completely rebuilt taking frames that were not I frames and using them as I frames in the new GOPs that create the new exported clip.
...keep in mind I didn't take out any frames or add any transitions. All I did was add ten frames of black and a fade to the beginning and recompression now has to take place.
So, the answer is, no...there is no software than can actually create edits in an MPEG stream and then re-export it to the same format without recompressing it. This is why intermediate codecs like CineForm and ProRes are popular with editors.
You can do it with DV and other intra-frame compressed formats because each frame is complete and separate and cutting the clips won't change each frame's structure, although even in these cases, any frames that have some effect or color correction applied, or are involved in a transition are still re-compressed.
Re: Export MPEG-2 without recompression by Koby Goldberg on Jul 6, 2009 at 4:38:09 pm
Hi Tim,
Thank you very much for the explanation.
However from what I know the GOP size doesn't have to be constant... it can change in the course of the DVD. This way commercial DVDs are made to achieve best quality: usualy each new scene (or camera cut) is starting a new GOP (with an I-frame).
Therefore in the example you gave, the first new 10 frames can create a GOP, the next 15 frames would be the second GOP (changed from the original because of the fade and would have to recompress), and the rest of the video could stay the same with it's original GOPs.
Moreover, I know it is possible because with an old MainConcept version (in PPRO CS2) I did it! I am not dreaming... :) I realy did it. The export ran very fast on footage that didn't change, and slowed down to render and recompress parts of the video that were added or changed. The time was 10:1 than the original video (if the video was 10min, the export to MPEG2 took about 1min), and that was on an older computer, so it could not have been a compression...
Re: Export MPEG-2 without recompression by Tim Kolb on Jul 6, 2009 at 7:12:56 pm
[Koby Goldberg]"This way commercial DVDs are made to achieve best quality: usualy each new scene (or camera cut) is starting a new GOP (with an I-frame)."
If this is what you want to do, it's not an NLE that does this...you need to add some other software to take care of that.
Re: Export MPEG-2 without recompression by Brian Louis on Jul 6, 2009 at 6:55:03 pm
[Koby Goldberg]"Is there or is there not another software that can do it ?" One is Videoredo.com it does frame accurate editing with smart rendering, I use it to touch up CITC recordings off of discs, its basically consumer software.
Re: Export MPEG-2 without recompression by Koby Goldberg on Jul 6, 2009 at 9:11:18 pm
Thank you very much Brian!
It looks great! I'll look into that!
What exactly does it do ?
Is it like a Video Editor for MPEG files, that combines and cuts parts of it without recompression ?
Tim,
What software did you mean ?
Something like Brian suggested ?
p.s.: From what you both are saying, I understand that PPRO cannot do those accurate editting and smart compression... I hope that for AVCHD compression they CAN do it, because it would be quite a shame for someone to import AVCHD footage from a camera and need to recompress the whole video again after minor editting... (HD is much much slower)
Re: Export MPEG-2 without recompression by Tim Kolb on Jul 7, 2009 at 1:41:02 am
[Koby Goldberg]"Tim,
What software did you mean ?
Something like Brian suggested ?"
Sure...the thing is that you've done this with DVD MPEG2 most likely...AVCHD and HDV have some pretty straightforward and rather tight standards and I'm not sure you can manipulate the GOP lengths and still have a file that is recognizable as AVCHD or HDV when you're done.
Re: Export MPEG-2 without recompression by Brian Louis on Jul 7, 2009 at 2:34:52 am
[Koby Goldberg]"Is it like a Video Editor for MPEG files" Yes
[Koby Goldberg]"that combines and cuts parts of it without recompression" Usually if straight cuts, or drop-ins for the same material its mostly without recompression except to mend the cut GOPs
AVCHD should be used with a intermediate codec like cineform, neoscene, the compression is so high it can choke most systems when codeding/decoding, the loss with transcoding to a intermediate codec is minimized by going by going to a higher bit count and quantization.
Re: Export MPEG-2 without recompression by Koby Goldberg on Jul 7, 2009 at 5:12:39 am
Thank you very much guys !
I will check out the VideoReDo software you've mentioned.
I will also check the mentioned EDIUS if it can provide what I'm looking for. From what I've read, EDIUS uses MPEG2 natively and uses the powerfull PROCODER compressor for exporting, maybe it can change the GOP sizes and recompress only the needed parts. If it does, it would be more convinient for me than the VideoReDo because of the full NLE capabilities EDIUS can offer (Transitions, Effects etc.).
If you have any other ideas or software I could also try, I would love to hear!
