[pawel]

Quality of re-rendered video will decrease as mpeg format is lossy - it's like double encoding mp3. You should demux and leave video as it is now, and add (mux) to it synced audio.

105 minutes of video and audio in LPCM format of a DVD5 would require to render video at 4276 kbps average. If you save audio in Dolby 192 - 448 kbps, average video bitrate can be raised to 5600 - 5300.

8100 kbps everage is nonsense as the quality of your source is not at this level.