But as stars usually have tight schedules, it's hard to bring them all together at the same time and place.

"So, you can see from most promotional clips stars wear headsets and read from a copy of a script alone in a sound-recording studio. And, for those who are not professional enough, it's easy for the process to become an exercise in line-reading rather than a voice-over performance," says Cao.

Also, because some stars have strong accents, it can sometimes sound weird, he says, to hear cartoon characters speak like that in a standard Mandarin version, he adds.

Li Baochuan, a researcher of animation history at Hangzhou Normal University, echoes Cao's views on the need for good voice-over work when he recalls that the 1999 animation Lotus Lantern gained huge success, partly thanks to its star-studded voice-over cast of more than 10 celebrities, including Jiang Wen, Chen Peisi and Zhu Shimao.

"It became a game-changer that ushered in a wave of big-budget animations that started to use celebrities to enhance the films. And veteran actors, who have stage performance experience, have proved that they can do a better job."