8 Replies Latest reply on May 6, 2011 12:47 PM by diggins123

    Exporting to FLV with trasparent background

    diggins123

      Hello all,

       

      I am finding myself in a bit of a delema...I have hundreds of little movie clips with trasparent backgrounds that need to be exported as FLV's.  From my experience (or lack there of) and knowledge, to find the best export settings to create a FLV that looks good with the lowest file size comes down to the good old trial and error method.  I've tried numerous different settings and to be quite honest, I can't really tell that big of a difference in the video when it's be exported at 200 kbps compared to 600 kbps.  Maybe I'm blind.  But, I do notice the size of the file(s) go up quite a bit.

       

      The quesions are...

      1. When exporting to FLV's with transparentcys, is it worth it to crop the frame size?  I've tried this a few different times and in fact noticed the file size go up after cropping the frame size.  One would think that the a file that is "smaller" in dimensions would be smaller in size.  Although, I guess it's more about the information being translated in the video.

       

      2. Is there a trick to this exporting to FLV beast?

       

      Thanks in advance!

        • 1. Re: Exporting to FLV with trasparent background
          Colin Brougham Level 6

          The only determinant of file size (or at least, the most directly manipulable one) is bit rate. Lower bit rates mean smaller files, higher bit rates mean larger files. It doesn't really matter if the file is 160x120 or 640x480: if the bit rate is the same, they'll be virtually identical in file size.

           

          Typically, as you decrease bit rate, you can (or should) decrease frame size and/or frame rate to maintain a modicum of quality. As the frame size increase, so too should the bit rate. Think about putting a kid's t-shirt on a 40-pound kid; now put the same t-shirt on a 400-pound sumo wrestler. Same amount of material, but more area to cover.

           

          Finally, when you chose a frame size, stick to dimensions that are multiples of 16. The way the codec used in FLV works--that is, On2 VP6--is to be most efficient when dimensions are "mod16." This is due to how the codec slices the image into blocks for compression. This is a good resource for that information: Optimal frame dimensions for Flash video | Adobe Developer Connection

          • 2. Re: Exporting to FLV with trasparent background
            diggins123 Level 1

            Thanks for the reply and the link!

             

            That all makes sense, I'm just kind of in a bit of a wierd position due to the odd size of this course that these flv's are going into.

             

            Thanks again for the help and knowledge!

            • 3. Re: Exporting to FLV with trasparent background
              Colin Brougham Level 6

              That all makes sense, I'm just kind of in a bit of a wierd position due to the odd size of this course that these flv's are going into.

               

              Are you specifically locked to a certain size? Do you have any flexibility? If not, what size do you have to use?

              • 4. Re: Exporting to FLV with trasparent background
                diggins123 Level 1

                Well, I do have some flexibility, but there's a ton of flv's being dynamically loaded into a e-learning course.  Almost all the screens are 1018x550 and are loading in at a 0, 0 (x&y) coordinace of the shell swf -- so all the flv's load in the same place and the positioning of the objects in the video (mostly talking heads, our waist up on green screen) is done in the video editing.  So, basically all we have to do is load the flv's at 0,0 and not worry about the x,y of all the screens.

                 

                Though, I must say that I did try to export a few clips that were cropped to be close to 1018x550 in mulitples of 16 and I really couldn't tell much of a difference.  I went from 200 kbps to 512 kbps...and to be honest, I can't tell a ton of defference with any of the clips I've exported at the higher bitrate (frame size multiples of 16 or not).  Do get me wrong, you can see that it is a bit better, but nothing like "oh my God."

                 

                It's just this big battle of size vs. quality and they video's need to look nice, our client is a pretty big client and have "high standards".  I just feel like I'm missing something.  I see these video's online that look beautiful and clear and aren't that big in file size...what's the secret? haha!

                • 5. Re: Exporting to FLV with trasparent background
                  Colin Brougham Level 6

                  Though, I must say that I did try to export a few clips that were cropped to be close to 1018x550 in mulitples of 16 and I really couldn't tell much of a difference.  I went from 200 kbps to 512 kbps...and to be honest, I can't tell a ton of defference with any of the clips I've exported at the higher bitrate (frame size multiples of 16 or not).  Do get me wrong, you can see that it is a bit better, but nothing like "oh my God.

                   

                  The mod16 "rule" is more of a guideline; in actual practice, the benefits are probably minimal. If anything, I suspect you'd see results more along the lines of a slightly faster encode, more than a significantly higher quality encode.

                   

                  At 200kbps with a roughly 1000x500 FLV encode, I can't imagine the video looks very good at all! Even at 500kbps, that's still an awfully low bitrate for such a frame size. I've typically used 600kbps+ for a 640x360 encode--that's less than 1/2 the frame size as your intended encode, and a higher bit rate. I don't know that I've ever exported an FLV with transparency, but I suspect that adds to the overhead as well.

                   

                  Are you using 2-pass VBR encoding? That's probably the best way to try to maximize quality and minimize file sizes.

                   

                  It's just this big battle of size vs. quality and they video's need to look nice, our client is a pretty big client and have "high standards".  I just feel like I'm missing something.  I see these video's online that look beautiful and clear and aren't that big in file size...what's the secret? haha!

                   

                  Well, if they're not transparent, they're probably using H.264, which is capable of producing far higher quality at lower bitrates than VP6, the FLV codec you're using. If you need transparency, though, your options are severely limited.

                  • 6. Re: Exporting to FLV with trasparent background
                    diggins123 Level 1

                    Yeah, I have been using 2-pass VBR encoding at this point.  I'm kind of wondering if it might be better to just include the backgrounds into the videos and export them as H.264...do you know if you can dynamically load H.264 into a swf?  Or, could I export to H.264, import the H.264 file back into Premiere and re-export as a flv?  I assume I'd still be stuck in the same position at the end of all of that though...

                    • 7. Re: Exporting to FLV with trasparent background
                      Colin Brougham Level 6

                      I'm kind of wondering if it might be better to just include the backgrounds into the videos and export them as H.264

                       

                      That would be an option. It really depends on what the page looks like that you'd be embedding these into. That's the nice thing about the transparency--you only really have to be concerned with the foreground. But, if your page is something simple, like a solid color, you'd probably get the same visual result by putting a color solid behind your keyed subject in Premiere, and exporting to a non-alpha clip, like an H.264 MP4.

                       

                      do you know if you can dynamically load H.264 into a swf?

                       

                      Umm... no I'm just a measly video guy

                       

                      Seriously, though, you may want to have a look at F4V; that will probably do exactly what you need, as it's H.264 compressed video in an Adobe-ized container format. It's available in the FLV/F4V options you've been working with. Just note that, since it's H.264, it does not support an alpha channel.

                       

                      Or, could I export to H.264, import the H.264 file back into Premiere and re-export as a flv?  I assume I'd still be stuck in the same position at the end of all of that though...

                       

                      Worse You'll have applied a second round of compression rather needlessly. You can use some third-party trickery to rewrap an H.264 stream into an FLV--I've actually done this before for HTTP pseudo-streaming web videos--but you still won't have alpha.

                       

                      I think this is just a matter of deciding how you want to fit the videos into the rest of the design. If it were me, and I had the flexibility, e.g. a solid background, I'd forgo FLV and use H.264 in an MP4 container or F4V instead.

                      • 8. Re: Exporting to FLV with trasparent background
                        diggins123 Level 1

                        Excellent feedback, thanks again for the brain sharing with me.  I'm going to do some test exports and then have a chat with my programmer if F4V seems to have the better quality compression for the file size.

                         

                        Thanks again!!!!