Author Topic: MPEG, Display the target square Pixel Ratio, from a croped mpeg.  (Read 4793 times)

twinsun

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MPEG, Display the target square Pixel Ratio, from a croped mpeg.
« on: December 06, 2013, 06:44:19 AM »
Display the target square Pixel Ratio, ie for x264, from a croped mpeg.

I'm used to caculate the square Pixel Ratio with Excel, but why not display it directly in the Crop filter windows, or best as input in swsResize ?

AQUAR

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Re: MPEG, Display the target square Pixel Ratio, from a croped mpeg.
« Reply #1 on: December 06, 2013, 01:04:47 PM »
I am not getting the meaning of this topic, but just my two bobs worth.

For square pixels the DAR of the cropped MPEG is simply equal to its SAR.
No excel spread sheet needed for that, nor is there a need to display the SAR for this.

When the DAR of the source is not equal to the SAR, avidemux needs more options to set the PAR of the target (output).
In copy mode it needs a configuration item for PAR and ditto for encoders (like it is for AVC in 2.6.x and Xvid in 2.5.6).
You will notice a DAR mismatch straight away since avidemux always displays with DAR=SAR.

IMHO such correction should not be done in the crop or SwsResize filters (ie at the pixel level).
You end up with bad recodes like the ones I sometimes DL.
Eg messed up scaling of 4:3 PAL video to fit in a 16:9 PAL frame (horizontally stretched).
These require an "inverse" PAR correction. 

DVB recordings also have a non square PAR and that is giving endusers some grief when using avidemux.


« Last Edit: December 06, 2013, 01:18:03 PM by AQUAR »

twinsun

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Re: MPEG, Display the target square Pixel Ratio, from a croped mpeg.
« Reply #2 on: December 06, 2013, 03:59:32 PM »
Crop a mpeg, then go to swsResize.
swsResize asks to choose 16/9 or 4/3 or 1/1.
Why enter something, when it can be proposed by default for the video you cropped, as all is known of it.

Often, I need to "calculate", to verify, or by need, example :
I post a small chunk of mepg (french section), for wich you can't find the solution if you do not calculate a bit.
It's out of swsResize press button. Try it !

What I suggest is to give by default to swsResize the right ratio, wich take care of the mpeg caracteristics and the crop you made.
So that you only have to choose the amount of pixels, wide or height, that's it.

AQUAR

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Re: MPEG, Display the target square Pixel Ratio, from a croped mpeg.
« Reply #3 on: December 07, 2013, 01:28:02 AM »
Thanks twinsun for the clarification.

Its fair enough to suggest that SwsResize could do with a default setting of source DAR = target DAR. As long as its not replacing the Broadcast/PC PAR options and unrestricted user defined SAR options.
You could argue similarly for the source to be displayed at its DAR and for the target to be displayed at its redefined DAR.

There are probably a few reasons why avidemux processes with square PAR's for its main operations.
I don't know what they are (but can guess a few - eg the KISS principle!), or if the developers intent to tweak avidemux for a more automated approach to aspect ratio's. 

Its not that big an issue once you know a bit about aspect ratio relationships and the type of display hardware used for playback.
And the main purpose of avidemux 2.6.x of being a basic AVC editor and recoder is not affected. 

That said, I get the feeling from recent posts that this aspect ratio issue is getting more important and perplexing to endusers.
Particularly so as increasingly they want to play around with dvb recordings.

« Last Edit: December 07, 2013, 08:52:05 AM by AQUAR »