private static void ValidatePlayRange(this IMediaSource mediaSource, PlayRange playRange)
{
if (!mediaSource.IsValidPlayRange(playRange))
{
if (mediaSource.HasNativeDuration())
{
throw new ArgumentException(
string.Format("{0}无效，有效范围为：{1}。", playRange, mediaSource.GetNativePlayRange()),
"playRange");
}
else
{
throw new ArgumentException(
string.Format("{0}无效，起始位置必须为TimeSpan.Zero。", playRange),
"playRange");
}
}
}
