6 Replies Latest reply on Nov 24, 2009 8:14 AM by TimeRemapper

    Mpeg2 Blues

    TimeRemapper Level 4

      Houston, we have a problem.


      Here's the synopsis:

      I've got a NTSC Widescreen DV comp in CS4 (720x480, 1.21 PAR - progressive).

      I render this file to a Quicktime (Animation codec @ best/full).

      I drop this file into my encoding software (I've tried Compressor, AME, and AME directly out of the Render Queue).

      I set the encoding parameters to match the file (DV NTSC mpeg2 - 16:9  - progressive).

      There's no cropping or padding, no image adjustments or effects applied.

       

      No matter what I do, the output mpeg2 file (from any of the encoding applications) appears to be cropping, and vertically stretching the material during the encode. I have NO idea why this is happening.

      Has this always happened, and for some reason I've never noticed? I doubt it, but anything is possible.

       

      To further the investigation, I made a test project of 5 full-width single-pixel lines at the top and bottom of a black comp.

      I then tried encoding this file, and saw the same results. I've attached the .aep (may take a while to get approved).

       

      I know this is not an AE problem, but I'm at a loss, and the folks who play in this sandbox are some of the brightest people I know.

      If you guys/gals have ANY suggestions, or can tell me where I've gone astray, please do.

       

      (original image from AE comp)

      dvWidescreenOriginal.png

       

      (encoded screenshot)

      mpeg2Result.png

       

      (comp settings)

      compSettings.png

       

      Thanks!

      -Steve

        • 1. Re: Mpeg2 Blues
          Mylenium Most Valuable Participant

          Are you viewing the material in an app that also supports PAR correction? You know, QT doesn't do that. The color shifts could on some level be explained with the compression model and chroma sampling, but I agree that it just looks ugly and quite severe. In any case you should get correct results in Adobe CS4 apps, external encoders may stil lwant the old aspect ratios. Also one thing to try is to encode from a square pixel comp and see if it is less prone to these errors.

           

          Mylenium

          1 person found this helpful
          • 2. Re: Mpeg2 Blues
            TimeRemapper Level 4

            Thanks Lutz.

             

            I tried viewing in MpegStreamclip, Quicktime, DVDStudio Pro, and our Sonic system.

            Good idea on the Square Pixel comp. I'll try that.

            The color shifts I'm unhappy with, but I'm more concerned with the apparent vertical cropping and resizing.

             

            I just tried encoding from a Square Pixel comp, and same results.

             

            • 3. Re: Mpeg2 Blues
              Mylenium Most Valuable Participant

              Has something perhaps messed up your CoDecs? It's definitely pretty weird.

               

              Mylenium

              1 person found this helpful
              • 4. Re: Mpeg2 Blues
                TimeRemapper Level 4

                Thanks again.

                I don't think so, only because it's a fresh install of leopard (10.5.8), with all apps updated.

                Also, I tried this on a different rig (compressing), and got the same results.

                This all led me to believe there may have been something amiss with the source file, but I can't figure out what may be wrong with it.

                As always, your help is greatly appreciated.

                 

                Is there any way to strip PAR information or metadata from the QT file before I feed it into compressor? Perhaps there's something confusing the encoders that's embedded in the file?

                • 5. Re: Mpeg2 Blues
                  Rick Gerard Adobe Community Professional & MVP

                  Single pixel wide or high vibrant colors will almost always be fouled up by compression. I'm not surprised at all that things don't look right.

                   

                  Here's what I'd do.

                  1. Add a normal image (like a photo of your mom) to the footage.
                  2. Render your test comp to an uncompressed or lossless format first. Quicktime Animation at Best would do nicely.
                  3. If everything is OK, try the MPEG compression at an insanely high data rate.
                  4. If that works, lower the data rate until you start seeing the colors foul up in your single pixel lines and check out how mom looks.

                  I'll bet that mom will look great at a data rate that completely fouls up the single pixel lines.

                  • 6. Re: Mpeg2 Blues
                    TimeRemapper Level 4

                    Thanks for the suggestions, Rick!