Question

I want to know if it is possible to use javascript, flash or flex to make a youtube video player that is capable of controlling left/right audio channel volume. For example, mute the left channel and play right channel audio on both left/right speakers.

Answer 1

Yes, you should be able to control the YouTube clip’s sound properties via the static SoundMixer class; specifically with the SoundMixer.soundTransform property:
http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/media/SoundMixer.html#soundTransform

With the soundTransform property you will be able to set the leftToLeft and rightToRight properties that control the stereo mix of the sound being sent to the speakers.

For more info see the SoundTransform class:
http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/media/SoundTransform.html

Just be aware that Google keep the YouTube API locked down pretty tightly, so you can only control these properties as global sound settings. If you are playing multiple sounds/audio sources then you will be affecting the mix of all sounds playing within your Flash movie. You can’t get access to the SoundTransform instances for each individual video.