I have to do a lot of this too. I think of it as enabling random access to movies (the same logic applies to using sliders, etc).
With Sorenson you want to stop using the 'natural' key frame setting (which allows the encoder to make all decisions about when key frames are used) and choose to enforce extra key frames at regular intervals. For my material I use every 75 or 150 frames at 25 fps i.e. every 3 or 6 secs. I'm sure you don't need to make every frame a key frame. I've experimented also with the brief pause in playback - the conclusion for me was that it wasn't necessary once I had added regular key frames. I believe Sorenson is unusual in allowing a 'natural' setting which is great for low data rate but not good for random access. For MPEG1 I use a setting called closed GOP, but there is probably less problem with MPEG anyway ... -- Richard Tribe, BBC Interactive dept. > ---------- > From: Andreas Gaunitz P11 > Reply To: [EMAIL PROTECTED] > Sent: Wednesday, March 20, 2002 14:33 PM > To: [EMAIL PROTECTED] > Subject: Re: <lingo-l> What quicktime compression format? > > >>I'm trying to have 2 video tracks in one movie, and let the user > >>chose which track he wants to see at any moment of the playback. > > > > > >I've done a lot of that. The problem is that the new video track you > >switch to has to go back to its previous key frame, and build up the > >current frame, all the time trying to deal with a still playing > >movie. > > Ah, so my guessing was quite not too far off then. > > > >You can reduce any problems a lot by pausing the movie while you do > >the switch, giving it some time to get its act together before > >playing it again, > > Unfortunatley it's not an option in this case. > > > > or/and you could make the key frames more frequent. If you're using > >Sorenson, you may find that the key frame spacing was set to be > >quite wide apart, because Sorenson is often used for web video, > >where infrequent key frames may help to keep the file size down. Try > >setting the key frames every one or two seconds, and also pause the > >movie as you switch tracks. > > Yes, I've been using Sorensson (from Adobe Premiere) until now. I > could use any codec but I guess Sorensson is still adequate if I use > more frequent keyframes. > > > Thanks for the help! > > This e-mail (and any attachments) is confidential and may contain personal views which are not the views of the BBC unless specifically stated. If you have received it in error, please delete it from your system, do not use, copy or disclose the information in any way nor act in reliance on it and notify the sender immediately. Please note that the BBC monitors e-mails sent or received. Further communication will signify your consent to this. [To remove yourself from this list, or to change to digest mode, go to http://www.penworks.com/lingo-l.cgi To post messages to the list, email [EMAIL PROTECTED] (Problems, email [EMAIL PROTECTED]). Lingo-L is for learning and helping with programming Lingo. Thanks!]
