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Exporting to FLV

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Petr BergerExporting to FLV
by on Dec 5, 2010 at 3:59:12 pm

I need to export some projects for the internet site of my friend (he uses embeded raw FLV videos) and I have some problems with exporting to FLV.
My project is in PAL DV WIDESCREEN. I have no problems when I export it to MP4 - when I play it in VLC player, the minimized window with the video has 16:9 aspect ratio and thats fine. But when I export it to FLV, the video looks strange. It seems to be letterboxed when its minimized in VLC (it has black bars above and below it) and when I maximize it to the full screen, the video has black bars on the left and right sides. I have no experience with FLV, so maybe I'm missing something :-)
When I stretch the resolution of the project from 720 x 576 to 1056 x 576, it looks ok, but I dont know if this is the right solution. I didnt need to stretch anything when I'm exporting to MP4.


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Graham MacfarlaneRe: Exporting to FLV
by on Dec 5, 2010 at 10:47:42 pm

Your working with PAL DV Widescreen which has a pixel aspect ratio of 1.46. The FLV format doesn't support non square pixel aspect ratios so at render time AE converts this for you.

To check, go to your render queue job to the output module settings. You should see a yellow exclamation mark in the bottom left which says that changes to your output have to made to meet format constraints.

The black bars top and bottom are generated because you specified an output size of 720x576 (PAL DV Widescreen) but this will only look wide when displayed with pixel aspect 1.46. If displayed at pixel aspect 1 (FLV requirement) then your image would look very horizontally squashed. To prevent this AE scales down the size of the render whilst keeping the 720x576 area you specified so that you see all your comp without squashing. Unfortunately the top and bottom areas are now empty and default to black.

A solution for you would be to precomp all the layers in your final comp, then change that new comp to 720x394 (576 / 1.46 = 394) and square pixels.
Finally, change the scale of the precomp within this new comp to 68.5 (100 / 1.46 = 68.5). You might need something fractionally higher to avoid gaps at edges.

Rendering this out to FLV should work perfectly

Graham Macfarlane
3D animator and VFX specialist
London UK


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Petr BergerRe: Exporting to FLV
by on Dec 6, 2010 at 5:06:39 pm

Thanks. So this is better solution than changing it in the rendering options? When I'm rendering to FLV there is an option called "PAL DV WIDESCREEN SQUARE PIXEL". It automatically stretches the resolution to 1050x576, but I can adjust it to 720x394. Seems to be working too.


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Graham MacfarlaneRe: Exporting to FLV
by on Dec 6, 2010 at 6:29:42 pm

Ok now you got me curious. In principal what your suggesting sounds like an automated version of my previous suggestion so if it works great!

I tried your method out and it didn't work for me.
Where exactly are you adjusting the output to, is it:

Output Module settings > Resize > Resize to 720 x 394
Whilst also unlocking the aspect ratio from 1.44:79 (1.82)

Graham Macfarlane
3D animator and VFX specialist
London UK


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Petr BergerRe: Exporting to FLV
by on Dec 6, 2010 at 7:24:43 pm

Output module settings
Fromat -> FLV
than click on "stretch" and other options appears
custom -> Pal DV Widescreen square pixel
stretch to -> change the resolution (its pretty easy, I dont need to do any math if aspect ratio is locked)


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Graham MacfarlaneRe: Exporting to FLV
by on Dec 6, 2010 at 8:51:19 pm

I know what is going on. You must be using either CS4 or an earlier version! I'm using CS5 which appears to act differently on this issue.

Graham Macfarlane
3D animator and VFX specialist
London UK


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Petr BergerRe: Exporting to FLV
by on Dec 6, 2010 at 9:41:34 pm

Yes, I'm using CS4.


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