image processing - Comparing bytes in Ruby -

i have binary blob header of either jpg or mp4 file. trying differentiate between two.

when file jpg, first 2 bytes \xff\xd8. however, when make comparison blob[0] == "\xff", fails. when know blob[0] in fact \xff

what best way this?

this encoding issue. comparing string binary encoding (your jpeg blob) utf-8 encoded string ("\xff"):

foo = "\xff".force_encoding("binary") # blob bar = "\xff" p foo         # => "\xff" p bar         # => "\xff" p foo == bar  # => false 

there several ways create binary encoded string:

str = "\xff\xd8".b                         # => "\xff\xd8"  (ruby 2.x) str.encoding                               # => #<encoding:ascii-8bit>  str = "\xff\xd8".force_encoding("binary")  # => "\xff\xd8" str.encoding                               # => #<encoding:ascii-8bit>  str = 0xff.chr + 0xd8.chr                  # => "\xff\xd8" str.encoding                               # => #<encoding:ascii-8bit>  str = ["ffd8"].pack("h*")                  # => "\xff\xd8" str.encoding                               # => #<encoding:ascii-8bit> 

all of above can compared blob.