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Interlaced vs Progressive troubles
This is a General question, but I struggled to find a category. If it needs moving then please….
Also, I am relating my experiences and (empirical and puzzled) successes. But I see the commercial TV with some horrid examples of exactly what I describing as jitter. Is there a wider problem?
I use a Pana HDC HS700 camera and shoot in 1080 50p. I use Vegas Studio (and have tried other stuff) to edit/render for other formats (25p, 25i, smaller frame sizes etc.)
I struggled with this for a long time, because I assumed that because the source was progressive, I should use progressive as the method of rendering. I also assumed that if I rendered as Progressive, the Win players would not have to worry about de-interlacing. Then there was the fact that a DVD authoring system would take care of all that….except the jitter stayed, even though the Auth programme would turn the result into 25i..
I started to get “advice” about needing 25i if I wanted it to play on a PC and 25p if I wanted it to play on a TV (or VCVS) and at that stage I thought all was lost. How did I know where the thing was going to be played?
I got lots of stuff about PC inadequacy, bit rates (too big or too small), players not de-interlacing, blah blah blah
If I kept the result at 50fps, 50p worked fine. But if I tried for 25fps output (smaller file size, maybe use for DVDs etc) I had a terrible jitter problem using 25p. No matter what I tried I would get this frame-rate jitter, if I used progressive rendering. mp4 mpeg avi all had it. Playing on a DVD did not help.
At one stage with one edit product, I had the result being no good even at 50p, because it was actually 25fps with each frame duplicated…from a 50p source. Sorry. Just to let you knw what a quagmire I was in.
Then I started rendering in Upper Field first ( although LFF seems to work as well.) This happened by accident, because I used a template that I thought was 25p but was actually 25i. Suddenly the jitter disappeared. mp4, mpeg, DVD…not a problem
What is the story? Why does a 50p video have to be rendered to 25i to play smoothly? If I play a DVD on a DVD player rather than my PC’s DVD drive, _does_ it matter how the DVD vob file was made? etc.
So can somebody help this benighted soul? If they can they will be bekinighted! 😀
Nick
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5 Replies
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OK. I will be more specific. This is regardless of bit rate, frame size, as far as I can see.
I render from a 1080 50p source. I want to make various sized frames and files for say, DVD, others’ screen showing, upload etc.
I realise that a small frame size, enlarged to full scree, will look pretty grainy. Too much enlargement.
I realise that a low bit rate will cause smearing and blurring at the very least. Too much compression.
This is another issue.
If I render a video to avi, using x264 codec, Upper (or Lower) frame first, I get interlacing problems: lines across the screen when anything moves. If I use Progressive Frame method, I get a “ghosting” whereby AFAICS, instead of blurring slightly to allow the .lower frame rate to show smoothly, the result is a series of “stills” in each frame, for any part that moves: so the main,full density, say person’s hand, and also several other ghosted ones that depict its path across the FOV. This results in a jittery appearance.
I have posted up a still of the result.
EDIT: BUT WHERE IS IT?
If I use the Vegas native Program Stream PAL Widescreen, 25i, UFF, with mpeg-2 encoder (I can use DV encoder, but it limits size), CBR 9,800,000, with say, 720*400 frame size, I get a very reasonable output: freezing shows a small amount of compression smear, and the small frame can add artefacts. BUT there is no sign of ghosting. Each frame if frozen is fine, even in areas of high activity.
AND …there is no sign of interlace problems.
If I use 25p instead of 25i, I get the ghosting again.
So shy is the x264 avi package giving me _either_ interlace (25i) _or_ ghosting (25p), but the mpeg-2 avi package gives me _no_ interlace trouble at 25i, but ghosting at 25p?
I cannot remember a case where using 25p worked for me. As I said I assumed that was what I should use, as the original, which looks verrrrry nice, is 50p. If I render to 50p that works fine as well. IT’s on,y when dropping the frame rate.
Sometimes, depending on encoder, UFF or LFF give interlacing signs, others not.
Same goes with most of the Sony mp4 stuff that is available with Vegas Studio.
As usual I apologise if this is vague. I am still very confused, although at least now I can get some good outputs.
Thanks for any help
Nick
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Rendering 50p to 25i (eg MPG for DVD) should result in smooth, interlaced output when viewed on a device that correctly handles the interlacing (any PC media player with good deinterlacing, or any standard DVD player and TV). Some media players might not correctly handle interlaced x264 AVI.
To output 25p video (eg for youtube or only PC viewing), you’ll need to disable “resample” for each video event (right-click the event and choose Switches > Disable Resample). That will prevent Vegas blending two 50p frames to create one 25p frame. It will simply drop every second frame to give smooth 25p output.
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Oh good Lord! Thank you. I have asked about this so often, and been run around so many codecs and told this and that, and there it was. Disable Resampling. And those few extra words telling me how, which can be so heartening.
I am just so relieved, but a little peeved at all the times I have asked this and been given so much gobbledegook.
My apologies to anyone who is reading this and thinking “But I told him that!” At the time I was just getting so much info, most of it not Vegas-related, that I may have missed some.
So again, hero, thank you.
Gushing ceases. 🙂
Nick
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Glad to help. The “disable resample” trick eliminates ghosting for situations like this (input framerate is an exact multiple of output framerate).
Even when the framerates aren’t nice ratios (eg 24p > 25p) it might be better to have some jitter rather than lots of blending.
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You are helping me all over the place right now man! 🙂
yeah I am going to do some experimenting with non-half frame rate versions (25->24, 25->30, 50->30 etc) and the resample switch and see what happens. A whole new area of interest and probable frustration! 😀 I already tried a couple, because I read about the blend vs straight stuff with different frame rates after you gave me the lead. HAH! It was probably you that I read! It’s a tricky one. It’s a pity you can’t have a template that does it, so you don’t have to keep changing the switch on every event for different situations.
Nick
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