[Mp4-tech] MP4 file with more than one video tracks

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Hi,
I'm developing a media player the supports mp4 file with MPEG4 simple
profile 
but I've gotten problem when rendering a mp4 file with 2 video tracks 
and 1 audio track. 
Is this a legal mp4 file ? If yes, which video track should I render ?
I have consulted the MP4 system standard 14496-1 Ch.13 to
find some information. But the spec does not mention this.
Can anyone tell me how to render this file ?
Thanks !
Henry