There's a bg sound in the whole timeline, but there's a video page where I put flvplayback to hold the videos, so far I used stopallsounds on the buttons that will show the videos, and it mutes the sounds in video too,
how will I do it where the bg sound will mute or stop while it doesnt affect the sounds in the videos
first of all, it really depends on how your background sound is playing.
ideally it should be played through a SoundChannel. then, your videoplay button can be scripted to stop the sound channel from playing, and also begin the video. SoundMixer.stopAll should not be a first line of defense to quit sounds.
here is some code to get you started. the video player's name is "flvPlayer" and the play button is "playButton"
var sound:Sound = new Sound();
var sc:SoundChannel = new SoundChannel();