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Forums Compression Techniques Compressor: Why do deinterlace controls matter?

  • Compressor: Why do deinterlace controls matter?

  • Tod Hopkins

    February 25, 2009 at 7:22 pm

    Why does the Deinterlace setting in Frame Controls matter when you are not deinterlacing?

    When Fields is set to “same as source” the deinterlace setting should be meaningless. Except, it’s not. Changing the control dramatically effects render times. Why?

    I realize this is probably academic, but I’m wondering if I’m missing something or if this is actually as illogical as it seems on it’s face.

    Cheers,
    tod

    Tod Hopkins
    Hillmann & Carr Inc.
    Washington, DC

  • Daniel Low

    February 25, 2009 at 10:31 pm

    “When Fields is set to “same as source” the deinterlace setting should be meaningless. Except, it’s not. Changing the control dramatically effects render times. Why? ”

    Setting to ‘Output Fields’ to ‘Same as source’ simply refers to the scanning method, which could be either Progressive, Top field first or Bottom field first.

    You then have three methods of deinterlacing to choose from, Fast, Better, Best with Best taking considerably longer than Fast.

    So, if you have interlaced source and you want progressive output, you’d set Output Fields to Progressive and then choose a deinterlace method.

    If you are going from interlaced to interlaced, then you’d set ‘Same as source’ and ignore the deinterlace setting. Compressor only deinterlaces jobs that need it. (i.e. deinterlacing always needs to happen if you apply a resize)

    See chapter 20 of the Compressor manual for more details.

    __________________________________________________________________
    Fonts are like cologne:

    A bad choice speaks louder than a good one.

  • Tod Hopkins

    February 26, 2009 at 12:10 am

    [Daniel Low] “If you are going from interlaced to interlaced, then you’d set ‘Same as source’ and ignore the deinterlace setting. Compressor only deinterlaces jobs that need it.”

    Yes, that’s what the manual says, but it’s clearly not what the app does. That’s why I ask. Compressor definitely does NOT ignore that setting. If you set deinterlace to fast, fine. Set it to best and your encode times will increase 50-fold! So… why? If compressor is ignoring the setting, why do the compression times skyrocket.

    tod

    Tod Hopkins
    Hillmann & Carr Inc.
    Washington, DC

  • Daniel Low

    February 26, 2009 at 7:41 am

    “Yes, that’s what the manual says, but it’s clearly not what the app does. That’s why I ask. Compressor definitely does NOT ignore that setting. If you set deinterlace to fast, fine. Set it to best and your encode times will increase 50-fold! So… why? If compressor is ignoring the setting, why do the compression times skyrocket.”

    In that case, what codec are you outputting to and are you applying any resizing or other frame control?

    __________________________________________________________________
    Fonts are like cologne:

    A bad choice speaks louder than a good one.

  • Tod Hopkins

    February 26, 2009 at 3:00 pm

    Yes, resizing 1080i to 480i, MPEG2 for DVD. With deinterlace set to fast, the four minute show takes 1 hour. Set to “best” it estimates 50+ hours. I let that run for one hour and the estimate did not go down.

    From what I read, the time estimates I get fit other people’s experience with this setting. It’s just that it logically should not happen when fields are set to “same as source.” I presume it’s just an oversight in the programming, but I was curious if someone knows better. I could not find anything on line. It’s not really a problem as long as you leave it at “fast” when you set to “same as source.”

    Tod

    Tod Hopkins
    Hillmann & Carr Inc.
    Washington, DC

  • Daniel Low

    February 26, 2009 at 3:49 pm

    Well you obviously can’t go straight from 1080i to 480i, you have to deinterlace first. Why don’t you go straight to 480p??

  • Tod Hopkins

    February 26, 2009 at 5:43 pm

    [Daniel Low] “Well you obviously can’t go straight from 1080i to 480i, you have to deinterlace first. Why don’t you go straight to 480p??”

    Apparently not obvious to all of us. You don’t NEED to deinterlace when scaling down from 1080i to 480i, but I realize that most scalers DO deinterlace before scaling, especially software scalers. I’m sure you are right. And in order to maintain temporal resolution, it would have to deinterlace at 1080, prior to scaling. Ouch. No wonder it takes so frigging long.

    By the way, I am testing 480p, but I don’t like to lose the temporal resolution. I like 60 fields. Looks smooooooth. Upside is that going progressive does cut the compression time dramatically!

    Thanks. Consider me educated!

    Tod Hopkins
    Hillmann & Carr Inc.
    Washington, DC

  • Matt Campbell

    February 27, 2009 at 2:59 pm

    Not to keep adding to this post but why can’t you just leave the frame controls off. Thus avoiding the Resizing Controls and the Deinterlace option? When creating the MPEG 2 just use the Video Format tab and for Field Dominance use Bottom first for Interlaced material and set your frame rate. How important is it to use the Frame Controls for resizing?

    When I’ve tested this myself I got pretty decent results going from 1080i material to 480i SD DVDs.

    OS 10.5.5, Mac Pro 2 x 3 ghz quad-core intel xenon, 9 gb ram, with BM Intensity Pro card

  • Daniel Low

    February 27, 2009 at 3:15 pm

    I agree, unless you are using the best quality resize option, frame controls are best left off, or you could set them to automatic.

    __________________________________________________________________
    Fonts are like cologne:

    A bad choice speaks louder than a good one.

  • Tod Hopkins

    February 27, 2009 at 4:03 pm

    [Matt Campbell] “Not to keep adding to this post but why can’t you just leave the frame controls off.”

    Go ahead. I’m learning a lot. I turn them on because I went to set the resize controls to “better” or even best. I’m not sure if it matters but I’m pretty sure the settings aren’t there just to make me feel better. Also gives you access to anti-aliasing and detail enhancement.

    This thread inspired me to look into ways of not deinterlacing. Since you can’t go to 60p on DVD, this is not terribly relevant for this compression but might be for other applications (I do a lot of MPEG from servers). Squeeze has a “discard field” options. This works really well going from 1080i to 480i in terms of sharpness and aliasing, but you lose the temporal resolution altogether which gives it a less “smooth” feeling. TMPG has several methods, some of which seem to avoid deinterlacing but I have not tried them.

    What I discovered about Compressor however, was that it was actually doing a better job of deinterlacing than I had thought. It’s tough to avoid playback transformations playing back a widescreen DVD but when I did, I discovered that many of the artifacts I was seeing were appearing in playback for one reason or another. I also want to test Compressor going from 1080i to 1080p60 to create a fully progressive intermediate for compression. This should avoid all deinterlace artifacts but may introduce scaling artifacts that are just as bad. I have not tested.

    I also found that Compressor’s old deinterlace filter has a “discard field” setting that should work like the Squeeze setting. I could try that, though the Apple manual explicit maintains that the new function is “always” better than the old filter.

    Tod Hopkins
    Hillmann & Carr Inc.
    Washington, DC

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