As I previously mentioned, files take up more space than their file size.

+----+----+----+----+----+
|    |XXXX|XXXX|XX**|    |
+----+----+----+----+----+

|    | = Disk block
  XX   = File
  **   = Wasted space
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You need to round up file sizes to the next multiple of a block size.

use POSIX qw( ceil );
$filesize = ceil($filesize / BLOCK_SIZE) * BLOCK_SIZE;
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Directories also take up space, but I have no idea how much. Unless you plan on having lots of directories, the simplest solution might be to lower DVD_CAP by a bit. I have no idea what's reasonable, but 64k is probably not a bad start.

# Space for directories. No idea what's reasonable.
use constant DIR_BUF => 64*1024;

use constant DVD_CAP => 4707319808 - DIR_BUF;
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