You can change this duration using the "-d <duration>" option. If <duration> is positive, it is the total number of seconds of the stream to be played before closing down the session and exiting. If <duration> is negative, then -<duration> gives the number of extra seconds to delay after the time specified in the SDP "a=range" attribute. (As noted above, the default value for this extra time is 5 seconds.)
可以使用"-d <duration>" 选项，如果<duration>被设置为>0，程序将播放<duration>时长的数据流，单位为秒。如果设置为<0，那么程序将在流结束后延时<duration>，然后结束播放，其中流的播放时长有SDP参数"a=range"所指定。(如果是延时结束，-d的默认时长是5秒)
For example, if the SDP description contains "a=range:npt=0-25", then "-d 10" means "play the stream(s) for 10 seconds, then exit", and "-d -10" means "play the stream(s) for 35 seconds, then exit".
例如，对于SDP描述"a=range:npt=0-25"，参数"-d 10"的意思是"播放10秒钟时长的流，然后退出"，"-d -10"的意思是"播放35(25+10)秒，然后退出"。
You can also use the "-D <maximum-inter-packet-gap>" option to ask that the program shut down if no new incoming RTP (i.e., data) packets are received within a period of at least<maximum-inter-packet-gap> seconds. This option is useful if you are running the program automatically (e.g., from within a script), and wish to allow for the possibility of servers that die unexpectedly. (Note that "-d" and "-D" are different options, and may both be used.)
使用"-D <maximum-inter-packet-gap>"参数，程序在<maximum-inter-packet-gap> 时间内如果没有接收到RTP包，将自动退出。对于无人值守的程序比如自动执行的脚本，如果服务器意外宕机的，这样的参数将使程序不会挂死。
You can also use the "-c" option to play the media sessions continuously. I.e., after the end time has elapsed, the program starts all over again, by issuing another set of "PLAY" requests. (Note that if you're receiving data (i.e., you don't use the "-r" option), then this means you'll get multiple copies of the data in the output file(s).)
Note that you can combine "-c" with "-d <duration>" and/or "-D <maximum-inter-packet-gap>". So, for example, "-c -d 10" means "play the stream(s) for 10 seconds, then go back and play them again for another 10 seconds, etc., etc."
"-c"，"-d <duration>"以及"-D <maximum-inter-packet-gap>"可以合并使用。例如 "-c -d 10"的意思是播放10秒，然后重头开始再播放10秒。
Receiving unsupported RTP payload formats
Note: An "RTP payload format" for a codec is a set of rules that define how the codec's media frames are packed within RTP packets. This is usually defined by an IETF RFC (or, for newer payload formats, an IETF Internet-Draft).
编码中的"RTP payload format"定义如何打包音视频帧。
By default, the program will ignore any subsession whose RTP payload format it doesn't understand (because, if it doesn't know the RTP payload format, it doesn't know how to extract data from the incoming RTP stream).
However, if an input stream uses a RTP payload format that the program does not support, then you may still be able to receive this data, by using the "-S <byte-offset>" option. This option tells the program to assume that any such unsupported stream uses a very 'simple' RTP payload format, in which the stream's data is packed contiguously into RTP packets, following the RTP header. (In particular, the payload format must not use interleaving.) <byte-offset> specifies the size (in bytes) of any special header that follows the standard RTP header. (This special header is skipped over, and is not interpreted at all.)
但是，即使不认识RTP的载荷格式，程序还是有可能接受数据，通过使用"-S <byte-offset>"参数。这个参数告诉程序，对于不认识载荷的RTP包，程序将流理解为一种简单的载荷格式，即流将音视频数据连续打包，并且紧跟在RTP头之后。(In particular, the payload format must not use interleaving.)<byte-offset>是紧跟着标准RTP头的数据长度。程序将跳过这一长度，不做任何操作）
For example, if the program didn't already handle PCM u-law audio ("audio/PCMU"; RTP payload format code 0), then you could receive it using the option "-S 0". If the program didn't already handle MPEG audio ("audio/MPEG"; RTP payload format code 14), then you could receive it using the option "-S 4" (because the RTP payload format for MPEG audio, defined in RFC 2250, specifies a (basically useless) 4-byte header at the start of the RTP payload).
例如，如果程序不能够处理PCM u-law audio ("audio/PCMU"; RTP payload format code 0)，如果你知道是这个编码，那么通过加入"-S 0"，程序将以一种连续的方式提取音视频数据。如果是MPEG audio("audio/MPEG"; RTP payload format code 14)，那么使用"-S 4"，因为RFC2250中定义的MPEG为音频编码格式指定了4-byte头。
Changing the output file buffer size
If you see an error message "The total received frame size exceeds the client's buffer size", then this indicates that incoming RTP data formed a frame that was too large for this program's output file buffer. By default, a 100 kByte buffer is used, so this situation usually does not occur. (It occurs only for codecs - such as JPEG - that can have very large frames.)
If, however, you see this error message, you can increase the output file buffer size using the "-b <buffer-size>" option.