What exactly does "frame based" render REALLY do?

[PuzZLeR]

Greetings folks.

This is in light of a recent thread here which came up in a search for information that I'm looking for. However I felt it best to begin a new thread on this instead.

I've been experimenting with the frame based option of VS since I dislike the "raking" etc of interlaced content on my particular monitor. Yes, I understand that different displays handle it differently.

My source is from my DvR at 29.97fps and interlaced. (I'm in NTSC land.)

Assuming all video is MPEG-2 at DvD compliant specs, I have a few questions:

If I edit and render this content to 29.97 fps as "frame based" with VS, what exactly does it do to the video? Is it really "progressive" or "interlaced with progressive frames"?

Isn't true progressive content that which is 23.976 fps? Wouldn't you need pull down instead, or something like that?

So I imagine that "progressive content" at 29.97 fps isn't really true "progressive content". All you're really doing with "frame based" at 29.97 fps is adding something like a filter instead to give it a certain appearance for certain monitors when in essense you're really destroying quality.

So if that is the case, as my last paragraph mentions, then wouldn't you be better off not using "frame based" and deinterlacing on playback with a decoder instead?

Forgive my lack of knowledge if this question is stupid but I am curious about this. (That's why I search and read forums. )

Thanks for reading.

[Clevo]

I think it's a great question and I look forward to reading the discussion

[etech6355]

So if that is the case, as my last paragraph mentions, then wouldn't you be better off not using "frame based" and deinterlacing on playback with a decoder instead?

Yes, my ATI video card has HighDef Accelleration along with hardware de-interlacing. When my computers display card is connected to the TV then i turn off de-interlacing on the 2nd monitor. The 1st monitor (computer screen), de-interlacing is turned on.
Interlaced video is NTSC/PAL 60/50 pictures per second.
Framebased is NTSC/PAL 30/25 pictures per second.

I don't know the method that VS uses to de-interlace an interlaced video. Some programs only use the top field & discard the 2nd field, others blend or interpolate the 2 fields together. Some programs give you a choice on how to de-interlace the video. I would guess that VS probably blends the fields together.
It can become a complex subject but rule of thumb is to keep your output file the same as the source videos.

You can read all you want on the web but I feel that many people get the term "Video Format" that ones camcorder records in confused with a TV's or HDTV's "Display Modes". It is confusing. I've read on the web where some say "Oh, you have an LCD TV so you have to de-interlace your video because LCD's are frame_based", Not True at all. You connect your cable to this LCD TV correct? That's an interlaced video signal.

You don't need to read much further whether to de-interlace your video or not if you shot it with a standard or highdef camcorder. Just capture some DV.avi with your cam and record some motion (panning, cars passing by etc), this will be fielded as LFF (lower field first) in the cam, capture it and export it to a dvd compliant file using LFF interlaced video. Make sure it's dvd compliant. Then export the same video and change it to Frame_Based when you export it. Now you have 2 files on your harddisk, a fielded video and a frame based video.

Open up a new session of VS and goto "share -> create disk", insert the fielded video & then insert the frame based video. Name each one appropriately in the menu creation (also make sure "Do not convert dvd compliant files" is checked "ON" under the GEAR Icon "Project Settings". Burn a fast dvd, don't use menu transisions, motion menus, fades or background audio to make it fast. In this example you DO NOT want the VS burning module to re-render your videos (or this test will not work).

Then play this test dvd in your dvd player. You will see a hugh difference in better motion with the interlaced video. Also test it playing back as "Progressive" if your dvd player & TV can do progressive. You will have the same results. The Progressive feature on dvd players is a "Display Mode", it cannot make up for the 30 pictures per second you took out of the video when you de-interlaced it. But it can sure use the interlaced video to progressively scan both the fields and make the picture look better.

[PuzZLeR]

@etech6355,

Thank you so much for your thorough and well put-together reply. I have responded now after wishing to do some tests.

Yes, I've done exactly as you said and more. I've even went as far as converting different files to different formats such as DivX, and even other apps with H.264 to see what results I got with each.

I have come to the sad realization that if the source video is interlaced, and you render it to "frame-based", the quality does indeed suffer.

I have no clue myself as to what VS does do with "frame-based", but I would bet money that it eliminates half the fields, not blends. This is the only conclusion that I can draw since it seems to create "interlaced video with progressive frames".

I'm actually sad because I have used this very feature for a portion of my encodes, and since some of the source is no longer available, I have lost this extra quality forever.

It's not a horrible difference, but if you were to play frames directly after each other, you would notice a difference nevertheless.

...a sad day indeed...

[daniel]

@etech6355,
I have no clue myself as to what VS does do with "frame-based", but I would bet money that it eliminates half the fields, not blends. ..

You cannot "blend" two half-pictures that were taken 1/50th or 1/60th of second apart. Things may have moved in-between and the result would be a horrible fuzzy mess.

Most programs drop one or the other frame and repeat the lines to fill the frame. A few do compare the fields and merge macroblocks WHEN IDENTICAL (no movement, like in a slide show or equivalent) to get better resolution. But it's a risky business. The best take into account the previous and following image and try to interpolate.

I don't know what Ulead does, before you ask...

Moving pictures should be kept interlaced at all costs if the end display can use interlaced contents. It is MUCH smoother.
You must understand that having interlaced contents means you in fact have lost half of the lines from shooting time...
People complain that 75 FPS is worse than 85 or more, so why would you settle for 30 instead of 60?
Computer monitors don't handle interlaced contents very well.

HD will solve this and much more (color space, definition etc) if they don't choose 720p because then we go back to 25/30 fps. Pray for 1080i to succeed.

All the above refers to interlaced contents, if the original contents WAS progressive there is no point, the fields are identical and resolution is doubled. That shows only on freezed frames though.

[TimmyTutone]

I have come to the sad realization that if the source video is interlaced, and you render it to "frame-based", the quality does indeed suffer.

I have no clue myself as to what VS does do with "frame-based", but I would bet money that it eliminates half the fields, not blends. This is the only conclusion that I can draw since it seems to create "interlaced video with progressive frames".

Frame based means that the video source was recorded in frame based (progressive mode), so I'm sure VS is just telling itself to not expect interlaced content. I don't think it does anything but squish the frames together if you choose it on interlaced content. That's why it would look awful. If you want to deinterlace it you could use scripting to deinterlace it, and send it through AVISynth (google it) before running it through VS for your final product.