[MPlayer-dev-eng] NSV demuxer

[Roberto Togni]

Hi all!
I committed a demuxer for NSV (Nullsoft streaming video) format.

Many thanks to Reza Jelveh for the patch (backport from G2, extensions  
and fixes).

Working stuff:
- VP3 and VP6 video
- mp3 and AAC audio
- streaming

Nonworking stuff:
- VP5 video
- VLB audio (what is it?)
- PCM audio (never found it in the wild, but very easy to add it if  
needed)

To be added:
- NSVf header parsing: it contains stream info like title and author,  
and some important stuff like aspect ratio and fps override (yes, you  
have fps stored in the stream but you can override it with a comment in  
the header!) and finally some kind of index.
- Seeking: coarse seeking should not be difficult, except for the  
keyframe issues; using the index (for nonstreaming files only) requires  
understanding how they work.
- aux data parsing: now it's just ignored; looking at vlc there sould  
be at least a SUBT subtitle data fromat (anyone have samples?)
- Other aux streams (ASYNC)
- fps computation for non so common cases
- Take into account audio/video sync offset from header
- Paanoid checks (codec change, broken streams)

To be fixed:
- keyframe detection. I can't believe that, in a file format developed  
about a year ago, demuxer must realy on internals of video codec to  
find out if a frame is a keyframe. So i hope there's a flag somewhere  
indicating keyframes. BTW, at least for VP6, there's no guarantee that  
the first frame in a block (NSVs) is a keyframe: you have to explore  
every subblock :(
- VP5: why doesn't it work? Is it just a keyframe issue?
- find out something about VLB audio

Ciao,
 Roberto