Security of Salsa20 with some known plaintext? Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known?

Assume that a different IV and Key are generated before each file is encrypted (or at least, it's statistically impossible for an attacker to know whether or not different files were encrypted with the same IV or key, and it's very unlikely that 2 in fact were)

I.e. the attacker will precisely know the first 64 bytes or so of the plaintext file, not the remaining mega/gigabytes, and does not have a comparison file which was likely to be encrypted with the same IV and Key
Yes, because there are no known weaknesses in (full) Salsa20.

http://www.researchgate.net/publication/226808260_The_Salsa20_Family_of_Stream_Ciphers