Tuesday, February 10, 2015

Avid Behaving Badly #15: Rendering a Scaled Effect on a Framerate Converted Clip Breaks Field Order

You know how sometimes you feel like you've dealt with all the weird shit that the version of Avid you're using is ever going to throw at you, and you're fucking Avid Superman around the office?  And then this happens.  This weird, absurd, ridiculous problem.

I mean, I just wrote that title, which is an exact description of the issue, and it still looks like goddamn gibberish.

So what error am I talking about?  Well, none.  Avid doesn't give an error in this case, it just spits out video that's corrupted.  If you, unlike Avid, know what fields are, the rendered video has the fields out of order.  The resulting image looks like it has scan lines, or some kind of fucked up interlacing, or something.  It's all shitty looking on the screen, basically.

Now this is a rare issue.  It seems to only happen when you do all of the following:
Step 1) Convert the framerate of your source video clip to another framerate, either by editing with it in a different framerate project, or by exporting the clip as a different framerate and then re-importing it.
Step 2) Put a scaling effect on the clip such as 3D Warp, Pan and Scan, or Resize.
Step 3)  Render it.

That's the thing - the effects look and play FINE unrendered.  It's only when you render them that Avid decides to shit the bed.

If you're like me, you'll assume that the rendering is the problem (but it isn't).  I tried every fucking render setting combination that's goddamn possible, and the problem still occurred.  So what the fuck?  A video mixdown is essential a media file of a render, and that still has the problem.  Exporting the clip is the same.  Exporting the source clip in the new framerate and reimporting it as the same framerate as your project, and then putting the effect on it still has the problem!  WHAT??

I suppose that, if I had a real-time playback to an actual tapedeck (and not a U1 drive), I could just hit record on the deck and play on the Avid and then let the output happen that way, but god damn if that isn't some bullshit and also not a thing I can do with my current hardware.

So how does one actually fix this nonsense?  Well, the big clue is that the problem really is the fields being out of order.  And there is one effect in Avid that can identify field order:  Timewarp.

But you can't apply a timewarp effect to a framerate converted clip!  So first you have to export the asshole clips in the framerate of the project that you're working in.  Strip off all of their FX, export them with 709 color space, full-res, in an Avid DNx codec of your proper framerate.  Note that for all of my example pics, I'm converting from 23.976 to a 59.94i project.  If you're going the other way, you'll need slightly different settings that pictured.


Then you need to import the video, ignoring alpha channels (why the fuck does DNx put the video on the alpha channel and have a blank video channel anyway?), and recognizing that 709 colorspace.



I stripped off the scaling effect and put a 100% speed timewarp on the source clip (that's normal playback speed; no time is actually being warped).  Then check the ignore render settings and set the render to "Both Fields."  Set the source video to "Film with 2:3 Pulldown" and the output video to "Interlaced" or "Progressive" depending on if you're in a 59.94i or 23.976p framerate project, respectively.  Click "Detect."

Then you can render that bitch.

Now apply your scaling effects to the rendered 100% timewarp clip, and they should render perfectly.

Fucking retarded that you need to use a motion effect to correct a field order conversion discrepancy, but that's goddamn Avid for you.

7 comments:

  1. Did you capture your source footage in a project with matching frame rate first or just into your 'editing' project? Love the blog title btw.

    ReplyDelete
  2. This error occurs when the footage is captured at a different frame rate than that of the project where the render is taking place. In my specific example, we shot and captured all footage at 23.976, and then were rendering it out at 59.94i.

    And thanks! "Avid hates you" is a phrase I used to use when training editors and assistant editors to explain why they need to save early and often while working.
    "Why do I need to back up so often?" "Because Avid hates you."

    ReplyDelete
  3. "But you can't apply a timewarp effect to a framerate converted clip!"

    You sound like you know what you're doing so I feel odd asking.. If you aren't aware of this feature, though, it can save you a ton of time.

    Did you attempt to "promote" the motion adapter on the clip? When Avid is interpreting mixed fps clips, it applies a general timewarp called a motion adapter. With your playhead over the clip, go to your motion effect editor and click "promote." Avid then converts the motion adapter to a timewarp that's just as customizable as any timewarp placed on native fps clips. No need to export/re-import.

    In fact, I would advise against export/import because that motion adapter effect (generalized timewarp) gets baked into your clip and now you're dropping frames or interpolating without a way to adjust.

    ReplyDelete
  4. Love the blog.

    We need change. Please, if you can help get numbers lets try get Avid actually sorted. A group of Editors in London have started this petition.

    https://www.change.org/p/louis-hernandez-jr-ceo-of-avid-avid-media-composer-sort-it-out

    Love the blog. Peace.

    ReplyDelete
  5. I wondered the same thing as Marc Schulter. Did you just enter the effects editor on your *difficult* clip, then promote?

    ReplyDelete
  6. It seems like you and Marc are saying that the framerate conversion done project to project is actually a promotable effect (though an invisible one)? I was not aware of that being the case, so I'll have to take another look at it and see if I can see what you're describing. Probably won't be until sometime next week when I've got the time to mess around with this situation again.

    ReplyDelete
  7. So I took a gander at this (sorry for the lag... been pretty busy with editing) and sure enough you can promote the non-effect clip to a timewarp proper. I did not know that, so many thanks to Marc Schuller for pointing that out! I don't think I've mentioned it here, but I'm entirely "on-the-job" educated when it comes to Avid, so I only know what other people have told me, or the small number of things I've discovered for myself (mostly enumerated in this blog).

    I still need to test to see if the promoted framerate conversion clips get the field order correct or if the promoted effect solves the issue (I imagine it would solve the issue). Again, I had no idea this was a thing, so thank you guys for pointing it out to me and saving me a ton of work in the future!!!

    ReplyDelete