Data CD directory record size question

how to know how many sectors are used by the directory records of a single session iso9660 CD before parsing each directory record?

I know the layout is “directory record area” followed by “file area”. Directory records size can be known if one knows the location of the first file on CD. Question: assume file A is the first file in root directory seen using a PC. Is A’s sector position the starting address of the “file area”?

I am not sure if this is the best forum for my question. Let me know if there is a better forum to post my question to.