Video file playback

[torquay7]

Hi all,
I just have a newbie question re: video file playback that I've wondered about for some time. With most video files, regardless of the format, you can scroll to another part of the clip/movie and continue watching. However, some videos freeze when this is attempted - ie. you have to watch from the beginning. This appears to be especially true of streaming videos that are downloaded/captured.
In lay terms ('cause I'm a complete eejit), why is this and is there a simple fix, such as a particular setting in a conversion tool like VirtualDub?
Thanks

[Baldrick]

You can try "fix" avi files using several tools like divfixpp, divx repair. wmv, asf files using asfbin or steeper.

Or try another player that might work better like VLC, KMPlayer, SMPlayer.

[torquay7]

I'll have a look at those programs - Thanks.

With the avi I have been attempting to edit, even VLC won't allow me to skip forward. This is why I'd like to know what causes this phenomenon in certain video files.

[redwudz]

Highly compressed video like Xvid/Divx only has keyframes (I frames) about every 300 frames. A 'I' frame is a complete frame. All the frames in between are referenced to it and contain only partial video data, most often just the changes in a scene. That's part of the way it's 'highly compressed'.

If the index in your video is messed up, your player may not be able to jump to the next keyframe and scrolling will be difficult or it may lock up the player. VLC, as mentioned, is one of the players that can ignore some of this and it works well with damaged video.

I have also had some luck running a AVI type file through VirtualDub and re-compressing. Sometimes even a direct copy works to repair the index. I most commonly see this problem with videos 'off the net'. I suspect they were encoded or edited improperly or damaged at some point.

And welcome to our forums.

[torquay7]

Okay, that makes sense. I can only surmise that there are other (good) reasons why the avi format is so popular.

Anyway, thanks for that explanation, and the welcome.