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Old 28th September 2010, 20:37   #1  |  Link
Klagar
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Help with WinFF parameters

Hi everyone,

I started a new job which requires me to dive into video encoding, a topic about which I've never given much thought. So now I am full of rather-newbie questions, trying to catchup with the train and become an expert in this field in as little time as humanly possible.

So here are my many questions. I just want to understand a little better those parameters in WinFF. I've checked the documentation available on their website, but it seems rather incomplete and vague.

Let's take a very real example which I have to deal with, and I hope someone out there can impart me some wisdom.

Command line :
-f avi -vsync 1 -vcodec libxvid -r 29.97 -s 1280x720 -aspect 16:9 -b 15000k -qmin 1 -qmax 31 -qcomp 0.6 -flags +loop+4mv+aic -me_method epzs -cmp +rd -subcmp +chroma -g 10 -async 1 -acodec mp2 -ab 192k -ar 48000 -ac 2

Questions :

-vsync : can anyone explain what could happen to a video file that has this parameter set wrong ?

-qmin/qmax : why is the maximum number permitted 31 ?

-flags : what is that ?

-cmp/-subcmp : what is that ?

-g : what values would you recommend ? Is there a value over which the video will inevitably lose a lot of quality ?

That should be it for now. Thank you for your time !!!
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Old 28th September 2010, 22:05   #2  |  Link
manolito
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Hi Klagar, and welcome to the forum!

IMO a software like WinFF aims to shield users from cryptic command lines like the one you mentioned...

WinFF is just a GUI for FFMPEG, and it comes with a full FFMPEG documentation (ffmpeg-doc.html). So if you want to dive into it, go ahead. But the usual approach is to select a preset which comes close to your needs and only change parameters if you know what you are doing.

Good luck

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Old 29th September 2010, 14:37   #3  |  Link
Klagar
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Hi and thanks Manolito !

In fact the thing is we do have a bunch of sets we use regularly and they work pretty well. Problem is, nobody here can understand what they are doing. Some presets were downloaded, some were built by people who are no longer working here, and some are just of unknown origin. I am in charge of building a complete documentation about what these parameters are and why exactly they were put in our presets. And then we can exploit them later, when we fully understand what we've been doing for some time.

You are not the first one discouraging me to use WinFF, but the fact remains that 90% of our products are based upon FFMPEG and our encoders all use WinFF and they made it clear that it would not change anytime soon. I just have to cope with it, for better and for worse.

As I said, I checked the documentation you mentionned, but informations are incomplete. For example, they don't say anything about -flags, -cmp and -subcmp.
You say I should change parameters only if I know what I'm doing. That's exactly the point : I want to know what I'm doing, and I'm presently taking small steps towards it. Most of the stuff seems pretty normal, but some other just eludes any attempt of mine at research and documentation.

So all that being said, can someone help a newbie who happens to stumble into a very esoteric realm ?
Thank you all !

P.S. Is there any other GUI for FFMPEG ? I would be interested, at least for my personal gain !
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Old 29th September 2010, 17:24   #4  |  Link
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No, I am not discouraging you at all from using WinFF, I do use it frequently, and I also made some custom presets for some friends.

You can find a lot of examples in the FFMPEG FAQ http://ffmpeg.org/faq.html , but you are right, there is no comprehensive reference manual for FFMPEG which covers all command line parameters. If you absolutely cannot find the information you need, it turned out to be a good idea to also search the Mencoder manuals. Syntax is a little different, but FFMPEG and Mencoder do share many options.

Another tip: You can get the complete list of all command line parameters with a (very short) explanation if you redirect the help output into a text file:
Code:
ffmpeg.exe -h >parameters.txt

With -cmp and -subcmp you can alter the motion estimation methods, I have never changed the defaults.

I use the -flags command for interlaced encodes. For a camcorder source these files are interlaced BFF, and I add the command:
Code:
-flags ildct+ilme+alt -top 0
This enables Interlaced Discrete Cosinus Transformation and Interlaced Motion Estimation and Alternate Scan Order. Also Top Field First is set to 0.

The -g parameter sets the GOP length. You have to follow the standards here. For NTSC DVD output a GOP length of 12 is compatible, 15 or even 18 are also legal if you do not apply pulldown.

And a maximum quantizer of 31 will give you a lousy quality already, nobody in his right mind would ever want to increase this value.


Cheers
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Old 29th September 2010, 20:12   #5  |  Link
Klagar
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Hi,

Thank you so much ! As it turns out, by reading other forums I learned just earlier today how to access the mencoder manual, and it put me on track for many things ; and you just helped me complete much of that info !

I think I've acquired much of the base already. I'll make sure to read as much as I can from the FAQ link you sent me.

Thanks so much !
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Old 29th September 2010, 21:40   #6  |  Link
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My pleasure....

Cheers
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