The lock symbol appears next to a video when the video has not finished transcoding. The transcode time takes about the length of the uploaded video. Once the video is done transcoding, the lock symbol will disappear and your video will be ready to add to the channel.
Note that if you left the page or edited the video name during the transcode process, the transcode progress will stop and the video will remain locked. If this happens, you will need to re-upload the video.