Flash video and precise skipping

0
votes

I am deploying a jwplayer (http://www.longtailvideo.com/players/jw-flv-player/) to a website and I am not 100% satisfied with the way the player behaves when you skip to a new position, you press the timeline at one spot, but it skips to a different location. (the elapsed time indicator)

This is also happening on youtube, especially on shorter videos: http://www.youtube.com/watch?v=hv7ha_iCM2Y

It seems this is a problem with flash video in general? Or can this be solved by using for instance streaming video instead of progressive HTTP playback?

Other things?

2
flashvideovideo-streaming
Flash Video player is really not precise. You have most of the time 5-7 images shift between real position and reported time. Maybe the developpers of flash video player have focused on network stuff. I don't even think time report accuracy was a requirement. Also Flash have much less ressources than VLC as it have no direct access to video acceleration most of the time. I struggled to develop an accurate video player for flash. I finally mange to do it but it took me months and it require special compression. I will post a link there soon if you're interesed. - bokan

2 Answers

1
votes

Skipping in an FLV will actually skip to the nearest video keyframe. You can increase the accuracy by encoding the videos with a higher keyframe density, although this will increase the file size.

1
votes

This is caused by something called GOP (no, not the Republican party) which is used when compressing video: http://en.wikipedia.org/wiki/Group_of_Pictures

In some compression methods the codec will need the information of the frames before to construct the actual frame and only every n-th frame (called a keyframe or I-Frame) will actually be stored "as is" - those are the frames you can skip to. This also means that it gets more noticeable on shorter videos as the scale of the time scrubbing gets more precise.