Filming Conversations
Crossing the Line
Establishing Shot
Usually, the scene is opened with the two characters in shot. This is to establish the relationship to each other in the scene: character 1 on the left and character 2 on the right.
Over the Shoulder 1
The camera moves to capture the face of character 1 usually from over the shoulder of the other character. As you can see Character 1 is still on the left side of the frame.
Over the Shoulder 2
The camera then moves to show character 2. Again an over the shoulder shot with character 2 remains on the right side of the frame.
This back and forth continues until the conversation has been completed. Some times the camera may stay looking at the character who is listening in order to show their expression/reaction to what is being said. Other times there may be a cutaway shot - a close-up of the hands as they fidget, which can also add to portray the mood of the scene. Check out this quick video tutorial from FX Home below.
Crossing the Line
Crossing the Line, The 180 Degree Rule, or Reverse Cut are all basically the same technique. By staying on the same side of an imaginary line it makes it less confusing for the audience to comprehend what is happening.
In front of the line
Staying on this side of the line, within the 180 degree rule, the characters remain in their correct position on screen as in the establishing shot. Here character 1 remains on the left because the camera has not crossed beyond the line.
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In front of the line
By crossing the line - going to the other side - and filming filming an over the shoulder shot, it suddenly puts character 2 on the left hand side of the frame which can be confusing for the viewer when the shots are cut back and forth between both characters.
Check out this short video on the 180 Degree Rule by Studio Binder