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1px black added to bottom of MPEG-2 ???
hi folks,
I am using squeeze to convert some 720×486 D1 avid source QT’s to MPEG-2 for DG FastChannel Upload.
The resulting compressed file has a 1~ pixel horizontal bar added to the very bottom of the picture. I have done numerous tests, and from what I can tell the picture is not being shifted up OR scaled- the black bar actually goes OVER the picture – I created a comp with a 1 pixel red edge to test this and the black replaced the bottom red line! What?!
Their specs prefer 720×486, but from what I understand MPEG-2 is a 720×480 format. In Squeeze, I “force” 720×486. This is where the problem occurs. My biggest concern is that my field order would get disrupted, but from all tests thus far, they look fine. THERE’S JUST A BLACK BAR AT THE BOTTOM.
I can relay my complete squeeze settings if anyone’s interested but I am quite positive the 480 vs. 486 dimension is the root of the problem.
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2 Replies
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We used to do export to DG/Fastchannel all the time and their preferred presets were indeed 720×486, MPG2 4:2:2. This is different from DVD/MPG2 specs so it’s not necessary to change the pixel size to 720×480 as you would for an MPG2 destined for DVD.
A viewer will never see that one pixel line if it’s at the bottom of the frame…so if you’re playback looks good, then I wouldn’t worry about it. DG/Fastchannel used to require a test file that they would evaluate and test before they’d clear you to provide digital files. Have you done this already or is this what you’re exporting the file for?
Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com -
Hi Chris, thanks for writing.
I don’t think DG requires a test anymore but I do specifically request it now, largely in part to this issue. And they do tell me that all is well. But I definitely still see it as cause for concern since, at least prior to my tests, it was unclear where that black was coming from and how it was affecting the dimensions and field order of my interlaced NTSC video.
For instance, if it was shifting the video up, even if that black line was out of action safe, there may be some other pixels further up that are now IN action safe after being shifted up a few pixels. But my biggest concern was fields and improper scaling due to any horizontal “squishing” – I mean if my source video is 720×486 and there’s a 2 pixel black bar added to the bottom, then where’d my other pixels go???
But DG claims all is well and my test indicates that the black bar is going OVER existing video which is better than any alternative. Still freaking bizarre and not cool.
I think I will post the specs sometime here and hope that someone would be willing to try them for themselves.
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