Videotaping conversations in the car are difficult scenes, but can be done well if you keep a few specific things in mind.
One of the most common film dialogue situations are those that take place in vehicles. Some of the most directed and focused conversations happen while driving, mainly because of the seclusion that occurs when being isolated in a moving metal box. This is often a difficult proposition for filmmakers because the physical dynamics of a car are hard to work around with a camera. There are certain things that you have to observe to make this work.
The most important thing to use when filming a scene like this are wireless lavaliere microphones. These are then placed lightly out of sight on each person, usually under the clothes. This way the audio will be clean no matter where you place the camera. If you are going to have more than two people talking then you are going to have to have a camera or sound recording device that will handle that many audio inputs.
From here you have to decide how and where to place the camera. The best way to do this is if the car is not moving. This is what is done most of the time in film, where the car is placed on a sound stage in front of a chroma key background. This is hard for most people to do on a shoe string budget, but you can make a free moving green screen backdrop to put behind the car. Then you can place the camera in the back of the car and record out the back window while driving for a while. Then you can replace that green background with the “back of the car" footage using chroma key tools.
If you are going to film while the car is in motion then you have a few choices to make. No matter where you place the camera you are going to get clean audio, so you are going to position the camera for ease of use and visibility. Placing the camera on the hood of the car pointed at the wind shield is great for visibility, but risky. You have to figure out a great way to secure the camera, but also so that it will not hurt the sight of the driver who may be driving on an open road. No matter what you should try to be on a closed or restricted roadway.
Filming in the car is also a great option, but it is tight and hard to get perfect angles. Try to do it in a fashion where each person does their lines on their own and then you can combine them using the rules of coverage. This is going to be difficult for filming the person in the passenger seat since it seems logical that the camera person would then sit in the driver’s seat, making it impossible for the car to be moving.
No matter what you do try to get good images that will convey all of the same things that a standard scene would. The dialogue is what is important, but you need appropriate visuals to support it.