I have follow code same as it is on different lines:
frame_rate = (float)
( ( ( frames * media_timescale) + \ //WHY???
( media_duration >> 1 ) ) /
media_duration);
I am not understanding what is backslash doing in source file ? Also to calculate the frame rate simply we can do as follow:
frame_rate = (float) ( ( frames * media_timescale) / media_duration);
Is there any specific intention to write first type of code?
It's a line-continuation escape. It means the compiler will consider the next line as a part of the current line.
It makes the code you show in practice being
frame_rate = (float)
( ( ( frames * media_timescale) + ( media_duration >> 1 ) ) /
media_duration);
There's no real need for it in this case though, except as maybe some style-guide followed by the author had it as a requirement.
Line continuation is needed to define "multi-line" macros, and are also often used for long strings. But besides those places, it serves no real purpose.