timeline左上角的嗽叭图标，去掉
具体请看：
To include or exclude an audio track from a composition:

Choose Layer > Switches > Audio to remove or add the checkmark by the Audio command.

By default, a check mark appears by the Audio command to indicate that audio is included for previews and rendering of the selected composition or layer. Audio icons () in the Features switches in the Timeline window also indicate whether or not audio is included.