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| -vdub- |
| Posted: Aug 16 2011, 10:16 PM |
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Advanced Member
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So what your saying for this video clip (link above) using any filter with any ar makes no difference. I'm at a loss there putting editing itself to one side since ar doesn't matter for that. I have always read that when make changes to a video it has to be done using the correct ar. Now i could mention many filters now (again not null transform or resize ones).
The way i see it a virtualdub filter process when complete will have modified the video and so an encode was part of the process. And would need to be done using the correct ar as video is at that time a filter is applied. Another way i look at it how many 5:4 pixels can fit inside a 16:9 pixel more than one. Use a filter at 5:4 and the video actually is 16:9 only part of each 16:9 pixel will be processed. Or do you thinka video is always 1:1 pixel square not matter the ar it says it is. Have a look at the 2 picture top right of this web page, one square one rectangle.
http://en.wikipedia.org/wiki/Pixel_aspect_ratio |
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| stephanV |
| Posted: Aug 17 2011, 04:46 AM |
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Spam killer ;)
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A pixel on your display has a shape, a pixel in a digital file doesn't have any shape. It's normally just 3 8 bit values telling what color it is. A filter doesn't work on the pixels on your display, it works on the pixels in a digital file.
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useful links:
VirtualDub, Input plugins and filters, AviSynth, AVI-Mux GUI, AC3ACM by fcchandler, VirtualDub FAQ |
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| -vdub- |
| Posted: Aug 17 2011, 05:56 PM |
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Advanced Member
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That reply has just cemented what i needed to know. Something that all sites i have visited over the years have failed to mention. From your reply i can easily see no matter what is displaying on the computer screen at any time makes no difference. Any filter or encoding will if chosen to alter all pixels and the sub macro blocks.
As you say the AR is only a flag which can be changed at any time much like Fourcc flags can be.
Great i appreciate you getting to this point i now understand in this one thread more for video than years of reading.
Thank You 
Any know tool for mpeg-2 that can change the SAR flag value. For example with restream i can change PAR and DAR even remove them both with only SAR remaining using ar of 1:1. Yet cannot find any that can change the SAR flag which i would like to do. Internet searches i have found can adjust any ar flag seen with gspot for xvid, divx, h264 and mkv i think.
Any MPEG-2 tool that can change the SAR flag value ? |
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| Placio74 |
| Posted: Aug 17 2011, 09:08 PM |
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VideoAudio
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If I'm not mistaken... there is no SAR flag.
Slightly simplifying, SAR it's just ratio of frame width/height (horizontal to vertical resolution). So obviously, additional flag is not needed (height and width value are sufficient).
BTW
Some data provided by GSpot (and not only) are result of analysis and calculation.
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VideoAudio.pl - Serwis o technologii wideo & audio |
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| -vdub- |
| Posted: Aug 18 2011, 10:26 PM |
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Advanced Member
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Then to change the sar video would need to be encoded again. Since 720x576 isn't a perfect ar for 16:9 sar value only will show 16:9 when the actual video is a perfect 16:9 ar.
Perfect 16:9 resolutions Aspect v2 that i used here. Doesn't show any of the high definition (HD) resolution information's atm. Problem with 16:9 and dvd is that dvd isn't made for 16:9 video instead actually everything is anamorphic so sad they had a chance instead butchered it to nothing. Better then to use BD or BDXL only for 16:9.
Is there a tool as Aspect v2 that also will show also HD resolutions ?
Here's a list of perfect AR for 16:9 from Aspect
macroblocks 32x32
512x288
1024x576
macroblocks 16x16
256x144
512x288
768x432
1024x576
macroblocks 8x8
128x72
256x144
384x216
512x288
640x360
768x432
896x504
1024x576
Macro blocks are video colour bits which also can be individually encoded to different I|P|B and intra frames ?
A quick test to evaluate this with ffmpeg default 16x16 macroblocks. Encoded to 512x288 and 1024x576 each video now has sar value of 1.778 (16:9) and will load to virtualdub using correct ar of 16:9
Still wonder each macro pixel will be square in shape since 16x16 is square. Are there 16:9 macro blocks to be used, maybe 8x16 or similar to match 16:9 or does the 16x16 fit inside a 16:9 pixel perfectly. Or maybe it is taht i have misunderstood something while reading informations for this. |
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| phaeron |
| Posted: Aug 23 2011, 05:15 AM |
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Virtualdub Developer
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Macroblocks are blocks of pixels that are grouped together for compression reasons. There are two fundamental operations in modern video compression that requires such grouping: motion prediction and image transform. The macro blocks are always in raw pixels, so if the aspect ratio causes non-square pixels, the macroblocks will also be non-square on screen.
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