Various newbie-questions

[tominator]

Hi
I have a few unanswered questions I was hoping to get answers for.

1. Why does the height of an encoded movie have to be a multiple of 8?

2. Encoded from the same source, would an xvid and a wmv have the same quality if the same bitrate was the same?

3. What is frameskipping? How much frameskipping is okay?

4. Is variable fps generally a good thing? When using it, do the parts of the encoded file where a lower fps is used get better quality/frame?

5. Am I correct if I say that it would be sensible to say that VBR suits local files and CBR suits files streamed from a server?

[CWR03]

1. Why does the height of an encoded movie have to be a multiple of 8?
It doesn't. For compatibility with certain players, it should be a multiple of 16, but for PC playback it can be anything.
2. Encoded from the same source, would an xvid and a wmv have the same quality if the same bitrate was the same?
There are too many variables to answer that, besides it would come down to a matter of your perception.
3. What is frameskipping? How much frameskipping is okay?
Frameskipping is leaving out frames during slow-motion scenes to reduce the needed bitrate. "How much is okay" is entirely dependent on your perception.
4. Is variable fps generally a good thing? When using it, do the parts of the encoded file where a lower fps is used get better quality/frame?
Variable FPS is good for animation. When the needed bitrate is reduced by having fewer frames, that bitrate is shared throughout the video, not just on the frames around it.
5. Am I correct if I say that it would be sensible to say that VBR suits local files and CBR suits files streamed from a server?
Not as far as I can tell (I use a media PC to view files streamed from a server and always encode VBR).

[tominator]

It doesn't. For compatibility with certain players, it should be a multiple of 16, but for PC playback it can be anything.

So if I know the files are only to be played in Windows Media Player 9 and above I can have any height?

Variable FPS is good for animation. When the needed bitrate is reduced by having fewer frames, that bitrate is shared throughout the video, not just on the frames around it.

By animation do you mean files with cartoon-like material?

Not as far as I can tell (I use a media PC to view files streamed from a server and always encode VBR).

But if you watch at a rather low bitrate, say 1500, wouldnt the VBR be at 1500 almost all the time anyway?

[foxyshadis]

If you have bandwidth limits, use the peak bitrate (or VBV as it's also called) setting to ensure that it never rises above that. Otherwise you'll always run the risk of either violating it or losing a lot of quality from being overcautious.

[Die*wrek*show]

4. Is variable fps generally a good thing? When using it, do the parts of the encoded file where a lower fps is used get better quality/frame?

afaik, there is another instance where you might benefit from variable fps. a video that has alot of intense action scenes could benefit from variable fps, in theory. i am thinking of the scene in the movie "abyss" where the rig crashes into the ocean. it was purportedly shot at very high fps, and wouldn't it make sense that in order to preserve the original scenes as accurate as possible, the fps would have to go up in those scenes to do so?