I don't think you need the "count"---ie dd will just go until there is no more data in the input file.
Try it several times---if it always stops in the same place, then it is probably a bad DVD. If it does something **different** each time, then the DVD reader is suspect. Try cleaning the reader and/or try the disk in a different reader.
Using Brasero works just fine though
What were you doing with Brasero?