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Old March 28th, 2013, 11:18 PM   #1
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SD resolution vs aspect ratio confusion

Hi guys,

This is probably a pretty basic question, but somehow it has me stumped. I don't often work with SD resolutions.

Basically I'm producing my first TV commercial (low budget, middle of the night kind of thing). The broadcaster requires the content to be delivered at 720x576 25P, 16:9.

The aspect ratios are confusing me. I have my Avid project set up as 720x576 obviously, but when I go to export the project at 16:9 aspect ratio, it stretches the file to 1024x576.

So I'm after an explanation on how PAL SD resolution works in relation to the aspect ratio, because it has me pretty confused. The commercial is ready for export, but I really need to get the settings correct. If anyone could provide a basic rundown on the Avid PAL SD 16:9 workflow, that'd be even better.

Thanks in advance.
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Old March 29th, 2013, 02:58 AM   #2
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Re: SD resolution vs aspect ratio confusion

1024x576 pixels gives 16:9 with square pixels.

720x576 gives 16:9 with rectangular pixels - width being 1.422 x the height.
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Old March 29th, 2013, 03:42 AM   #3
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Re: SD resolution vs aspect ratio confusion

Quote:
Originally Posted by Alan Craven View Post
1024x576 pixels gives 16:9 with square pixels.

720x576 gives 16:9 with rectangular pixels - width being 1.422 x the height.
Thanks for that.

However as above, outputting from Avid at 720x576 gives me 4:3. And selecting 16:9 makes it 1024x576. I'm guessing that's because the project consists entirely of images which would be square pixels?

According to the broadcast specs I have to follow, I need to deliver it in 720x576 16:9. Would I need to convert the images to rectangular pixels before importing to Avid?

Any Avid users here? Maybe this is a question for the Avid forum.

Last edited by Jody Arnott; March 29th, 2013 at 04:42 AM.
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Old March 29th, 2013, 09:55 AM   #4
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Re: SD resolution vs aspect ratio confusion

Hi Jody,

It has nothing to do with the type of media used IN the project, whether video clips or graphics. How does the TV station want the video delivered - tape, media file on disc, upload?

Widescreen SD is "anamorphic", which basically means "stretched". DV NTSC uses 720x480 for BOTH 4:3 and 16:9, and PAL NTSC is 720x576 for both. The difference between the standard and widescreen versions are the PAR (Pixel Aspect Ratio). With 16:9 video, the pixels are more rectangular for widescreen playback, or at least get interpreted as such.

So when using DV tape or DVD, the playback device knows if the footage is meant to be 16:9 and displays it accordingly. However, if playing a clip on the computer or online, the player software often assumes square pixels and thus plays back your widescreen footage as 4:3 (player assumes the pixels are square, PAR of 1.0). That is why your software wants to export as 1024x576 - divide each side of that by 64 and you will see that it is 16x9, which is correct for computer viewing (NTSC is 864x480).

I'm not familiar with how Avid works, and don't know what media the station wants from you, so can't suggest the best course of action in this case. Please let us know intended delivery format and station requirements.

Thank you
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Old March 29th, 2013, 03:22 PM   #5
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Re: SD resolution vs aspect ratio confusion

Quote:
Originally Posted by Jeff Pulera View Post
Hi Jody,

It has nothing to do with the type of media used IN the project, whether video clips or graphics. How does the TV station want the video delivered - tape, media file on disc, upload?

Widescreen SD is "anamorphic", which basically means "stretched". DV NTSC uses 720x480 for BOTH 4:3 and 16:9, and PAL NTSC is 720x576 for both. The difference between the standard and widescreen versions are the PAR (Pixel Aspect Ratio). With 16:9 video, the pixels are more rectangular for widescreen playback, or at least get interpreted as such.

So when using DV tape or DVD, the playback device knows if the footage is meant to be 16:9 and displays it accordingly. However, if playing a clip on the computer or online, the player software often assumes square pixels and thus plays back your widescreen footage as 4:3 (player assumes the pixels are square, PAR of 1.0). That is why your software wants to export as 1024x576 - divide each side of that by 64 and you will see that it is 16x9, which is correct for computer viewing (NTSC is 864x480).

I'm not familiar with how Avid works, and don't know what media the station wants from you, so can't suggest the best course of action in this case. Please let us know intended delivery format and station requirements.

Thank you
Thanks for the info.

The broadcaster requires the media to be delivered via FTP as follows:


"IMX30 QuickTime MOV or OP1a MXF wrapped
.mpg
4:2:2
30Mbit/sec
I frame only
Interlaced TFF
PAL
Standard Video Levels BT.601 (16-235. Not RGB 0-255)
16/9 FHA in NZ/Aus, International per broadcaster reqs
720(H) x 576(V) pixels
25.00 fps
Interlaced TFF or Progressive"


Avid has a same as source Quicktime .MOV export settings which spits out an uncompressed video file based on the project settings. I'm wondering if that will do the trick.

Not too sure what IMX30 is though. Might do a Google.


Thanks for any further info.

Last edited by Jody Arnott; March 29th, 2013 at 04:11 PM.
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