Permission denied

提示权限拒绝，怎么处理？
log回调：{"message":"/storage/emulated/0/Download/share_b7656c13a0dc1b1f2eecacb828e85bf8.mp4: Permission denied\n","sessionId":2,"level":16}

cmd：
let cmdStr =-i "/storage/emulated/0/Download/share_b7656c13a0dc1b1f2eecacb828e85bf8.mp4" -vf hflip -c:v libx264 "/storage/emulated/0/Download/done_custom_cmd.mp4";