3 Replies Latest reply on Apr 29, 2010 9:31 AM by Todd_Kopriva

    About finding good compression settings to email clips

    Dan Jacobsen Level 1

      Hi all,

       

      I want an easy way to email something I'm working on, usually anything upto 60sec.

       

      Copying some of settings the edit assistants use to email to clients here's whast I'm doing:

       

      Aiming for end size of clip to be near to but not much more than 5MB.

       

      Use Sor 3 at 426x240 (for 16:9)

       

      22.050 16bit mono audio

       

      I thought I could use these settings for all clips, then I could limit the size for different durations by changing the data rate.

       

      I thought if I divide 5000 by the number of seconds of the clip it would give me a data rate in K/sec that would then keep the size around 5MB.

       

      I wondered if I've got all this right? or if anyone had any other tips?

       

      Doing some tests I found 60sec @85 K/sec gave 4.9MB which sounds about right.

       

      But 60sec @ 250 K/sec gave 8.3MB which is less than I thought. (the edit assistants tell me they often use 250 K/sec for 60sec and get 5MB!?)

       

      Can anyone explain this to me?

       

      As I say, the aim of all this is to able to quickly work out settings that will produce an emailable QT.

       

      Cheers

        • 1. Re: About finding good compression settings to email clips
          Mylenium Most Valuable Participant

          Forget it.... I know this sounds harsh, but it's the only honest answer. CoDecs that use variable bitrate allocation, variable temporal spans and multiple levels of spatial compression are literally mathematically unpredictable - you don't know the result until you have run the clip through the algorithm. The effective data rate too much depends on the picture content. That's why in encoders it is always called "target bitrate", not final output bitrate. Only CoDecs that use fixed matrices, regular intervals and clearly structured visual compression algorithms can be calculated such as MPEG-2 and H.264, but even there is always a minor variability and uncertainty. It may not be convenient, but testing out settings for each clip is pretty much the only way, if you need to achieve a specific file size. As a rule of thumb you could base your guesstimates one third below the desired size/ data rate, i.e. if you need 5MB files, target your settings at 3.5MB.

           

          Mylenium

          • 2. Re: About finding good compression settings to email clips
            Dan Jacobsen Level 1

            Thanks Myl.

             

            That in itself is good to know. At least I know now that I'm not missing an important shortcut.

             

            I'll go with my vague equation, and when it doesn't work I'll just do it again.

             

            Cheers

            • 3. Re: About finding good compression settings to email clips
              Todd_Kopriva Level 8

              One thing to keep in mind is that you can decide what's important to preserve in the movie and then throw away a lot of the rest.

               

              I assume that the only reason that you'd be emailing a movie is for client review. So, what are you asking the client to review? Colors? If so, then frame rate doesn't matter, and you can drop the frame rate down to something really low. Timing and smoothness of animation? Then keep the frame rate high but sacrifice image quality and compress the bejeezus out of the images.