11 Replies Latest reply on Oct 22, 2010 12:33 PM by Shunshifuw

    compressing video

    saboo612

      i've got video (AVCHD) that i edited in premiere and when i export it the file is huge. my 15 minute video is the same size as a 1 hour video i downloaded. I made my video have the same file type (.mov), codec (h.264), resolution, and frame rate as the 1 hour video. but its still a much large file. what am i missing here? do i need to get another program to compress the file more?

        • 1. Re: compressing video
          Harm Millaard Level 7

          You need to use a lower bitrate when compressing, thereby lowering the quality even further or accept the larger storage space.

          • 2. Re: compressing video
            Jim_Simon Level 8

            There are only two factors that have any significant effect on file size, duration and bitrate.  If you want a smaller file, you need to reduce one or the other (or both) of those items.

            • 3. Re: compressing video
              shooternz Level 6

              ...what about pixel dimesions?  (Frame size)

              • 4. Re: compressing video
                Colin Brougham Level 6

                ...what about pixel dimesions?  (Frame size)

                Nope, makes no difference. A 320x240 encode at 500kbps is the same size (bytes wise) as a 1920x1080 encode at 500kbps. File size equals rate times time... kind of like distance equals rate times time.

                 

                For example, if you're on a riding lawnmower going 4 miles an hour, and drive for an hour, you go four miles. Now, if you get in your Ferrari, drive exactly four miles an hour for an hour, you go four miles.

                 

                Math: the reason I got into video

                • 5. Re: compressing video
                  shooternz Level 6

                  I usually find that I can reduce the frame dimension of a file (wmv)  without touching the bitrate and I get a smaller file size.

                   

                  Hey ...I am no math wizard but...I must check you out on that Colin.

                   

                  I cant even work out how to get this little forum post box to maintain line formatting!  The random word wrap drives me crazy

                  • 6. Re: compressing video
                    Jim_Simon Level 8

                    I usually find that I can reduce the frame dimension of a file (wmv)  without touching the bitrate and I get a smaller file size.

                     

                    Not significantly.  If the file size is changing to a marked degree, then either the duration or the bitrate have changed as well.

                    • 7. Re: compressing video
                      shooternz Level 6

                      Jim

                       

                      My test proves you (and CB) to be correct.

                       

                      I have been working under a delusion derived from my own ignorance of such matters.

                       

                      Maybe I need to go back to film school or something!

                      • 8. Re: compressing video
                        Colin Brougham Level 6

                        Ha! Don't sweat it--this compression stuff is some kind of dark art

                         

                        The discrepancies that you might see in file size would likely be caused by using a VBR (variable bitrate) encoding method. With VBR, you set a target bitrate, a maximum bitrate, and then there is usually an "undershoot" percentage that keeps the variability from going too low. When you encode a larger dimension video using the same bitrate, then encoder is cranking up the available bits to the 9s in order to ensure some semblance of viewability and to preserve a few more details, but this necessarily causes the file size to increase. It can only go so high (due to maximum bitrate cap), but that would account for any discrepancies you might see in output file size while using the same bitrate.

                        • 9. Re: compressing video
                          Shunshifuw

                          Yes I'm noticing some major file size differences with .flv files compared to .flv files I've created with other encoders. I'm running some tests to see what bitrates the other encoder was using.

                           

                          Any suggestions on bitrate for web video?

                          • 10. Re: compressing video
                            Colin Brougham Level 6

                            You're asking a different question, and should start a new thread. But yes--FLV and H.264 encoding is screwed up in CS5, particular when trying to encode to lower bitrates. File size end up far larger than they should, though it doesn't appear to actually be due to either the video or audio encoding, but rather something happening during the muxing phase to cause the bloat.

                             

                            I'm working on gather information to file a bug report--these encodes are bad right now and the situation needs to be fixed.

                             

                            EDIT: Here's a thread I started a few months ago that got a lot of discussion going </sarcasm>: Bloated FLV exports from Premiere/AME

                            • 11. Re: compressing video
                              Shunshifuw Level 1

                              Thank You Colin,

                               

                              Although I do seem to be having good results with f4v. I'm always interested in learning better compression techniques.