I'm a PC freak, so I can't help with a Mac program. Seems that you did all steps OK, what your soft allows to losslessly author a DVD. Small difference in total size of files is because of different size of menu(s).
Time difference can be due false information about DVD contents written by some standalone recorders, which is seen by computer players and authoring programes twice as large - the same video is "repeated".
However, if original video stream has an error, your authoring programe may not import whole video, so compare original and reauthored DVD if everything is OK.
Video bitrate can be changed two ways - see your program manual:
1.
Lossless by patching header of the first or all frames. It's like writting a text information to a video file, and not recompressing video itself. It's not neccessary. Sometimes it's done for (old) DVD players which incorrectly read information from the stream. For example first video header is set to maximum, and such bitrate is expected for all frames and red continuously by a player, while the real bitrate changes from frame to frame (variable bitrate, VBR). Also, headers of DVB captures usually have bitrate set over 10 kbps, which is outside DVD standard.
2.
Lossy: by rencoding video stream.
Anthing else to clarify?
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