This patch fixes Bug #8469
If x264 baseline profile is used with other profiles,
start_pts will be initialized to audio stream's first pts,
while the duration is calculated based on video stream's pts.
In this patch the start_pts is initialized with the correct stream's first pts.
Signed-off-by: Hongcheng Zhong <sj.hc_Zhong@sjtu.edu.cn>
Reviewed-by: Steven Liu <liuqi05@kuaishou.com>