In simple terms, the difference between video and audio is that video is for motion imagery and audio is for sound.
However the way in which video and audio are edited are distinctively different.
How Video Editing Works
When using simple video editing software like Windows Movie Maker or iMovie you only have one primary video track at your disposal. What this means is that whenever an edit is made it directly affects the video that is played back afterwards.
However, there is the option of adding simple effects like on-screen text that will appear to be “on top” of the video track. Technically speaking, adding on-screen text is a separate video track although it does not replace the primary video track unless you specifically instruct the software to treat text as such (such as introductory credits to a presentation).
With only a single primary video track, anything you place on that track will usually replace whatever video is already there.
How Audio Editing Works
While you will only be provided with a single video track with simple video editing software, you are provided with two audio tracks.
The first audio track is usually already used by the existing audio that is “carried over” from the video clip.
The second audio track is blank; it is provided this way purposely so you can add a secondary audio track, such as background music or sound effects.
It is usually possible to “break” the audio from the video track if you choose. This is normally called splitting the audio from the video. However bear in mind that is almost never required to split the audio from the video.
What edits are possible with video tracks?
With video the only edit you can perform on the track itself is a cut. This is where you literally cut the video at a certain edit point and replace it with another clip of your choice.
Anything else to do with video is either an effect or a transition. This will be covered in the next chapter.
What edits are possible with audio tracks?
With audio your options are usually limited to volume, fading in, fading out, and muting. In addition (depending on software) you can also make audio cut edits like you can with video cut edits.
Most software will also allow you to add audio, such as a soundtrack. This is technically not an edit; rather an addition.