There are two main problems with DVDs recorded in the field.
The first problem is missing frames. Portable DVD recorders that record straight to the blank usually can't keep up with recording video real time, so they skip frames when they get behind. DVDs recorded on portable decks are usually LOADED with these missing frames. They aren't apparent to the videographer who checks his disc on a DVD player, because all DVD players contain Reed-Solomon error correction that detects missing frames, and fills in for them using the frames before and after the missing frames. (The same error correction that prevents small scratches on the disc from disturbing the video.) This error correction covers up the problem, and makes videographers say "I've never had a problem" when you tell them they are giving you junk discs.
If you rip the VOB files from one of these discs with missing frames, and convert them to MPEG-1, the audio track is longer than the video track because each missing frame of the video is a small fraction of a second. After enough of them build up, the audio and video get out of sync, and the witness's lips don't match the sound you hear. I'm sure you've seen this many times in poorly made videos. MPEG-1 files made by ripping bad VOBs this way will usually crash programs such as Sanction when they are imported - probably because the program doesn't know how to handle video files with different video and audio run times within the same clip.
To fix those types of DVDs, they have to be played in a DVD player and re-recorded on a better recorder -- a model that contains a hard drive, and burns the disc as a dedicated process after the recording is finished. The recaptured discs can be ripped and converted safely because their VOB files contain no missing frames. I use Panasonic DMR series recorders, such as the EH67 and EH59.
The second problem with recording straight to the blank in the field is that there is no error detection done during the recording. If a defective DVD blank is used, there will be bad sectors on the disc that aren't apparent until the disc is played on the courtroom's DVD player or the client's laptop, at which time it will freeze and hang and possibly lock up the player. All DVDs recorded in the field -- even those from expensive hard drive equipped models -- MUST be read in a computer to verify that every sector is readable. I do this by making an ISO image of the disc using DVD Decrypter in ISO Read mode, but any ISO creation program can be used. If the program can make an ISO file from the disc without read errors, the DVD is ok. With portable recorders, burning straight to a defective blank means that copy is bad, and your only DVD master is lost. With hard drive equipped models, if a bad disc is found, you simply burn another copy to another disc from the internal hard drive.