In message , XPer writes:
Win XP Pro all updated.
Firefox updated.

Some on-line videos i can watch and some are scrambled and some say
"No compatible source for this media"

In some cases i can download and view in VLC but mostly I cannot download.

What am i missing ?
How do I view them ?

See Paul's for the usual in-depth answer, but just for clarification: do
you really mean you cannot download at all, or do you just mean you
cannot view what you've downloaded (in VLC or anything else)? If it's
the downloading that's the problem (which _is_ what you say), then
discussion of CoDecs won't help.

(FWIW, I can download _most_ things - from YouTube and other sites -
with my Firefox 26 and a plugin, though in many cases I _can't_ view
them within the webpage; the few I can't even download are mostly new
and "official" things, like movie traders or pop videos, where I assume
DRM is stopping me downloading. Which I _suppose_ is OK [though seems a
bit mean for trailers, rather than the whole film].)
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

The average US shareholding lasts 22 seconds. Nobody knows who invented the
fire hydrant: the patent records were destroyed in a fire. Sandcastles kill
more people than sharks. Your brain uses less power than the light in your
fridge. The Statue of Liberty wears size 879 shoes.
- John Lloyd, QI supremo (RT, 2014/9/27-10/3)