SourceFile syntax

LEADTOOLS multimedia gives some filenames special handling. These filenames follow a syntax similar to an URL (xxxxx://yyyyyy/zzzz):

1. Filenames starting with "http:", "https:", "ftp:" or "mms:" are assumed to be streamed from an URL. These filenames follow the standard URL syntax.

2. Filenames starting with "ms-http:", "ms-https:", and "ms-ftp:" are downloaded using the DirectShow URL file reader and are seekable. They use the "http", "https", and "ftp" protocols respectively. These filenames follow the standard URL syntax.

3. Filenames starting with "ltsf" are assumed to be streamed from a LEAD Streaming server and the LEAD Network Source filter is used as the source filter.         

   • The filenames should have the syntax ltsf://*ip_address[:ltsf_port]***.These streams require the videoconferencing component of the LEADTOOLS Streaming Module.

   • In particular, the LEAD Network Source Filter, LEAD Network Demultiplexer Filter and LEAD Network Protocol Manager are used for this functionality.

4. Filenames starting with "saic" are assumed to be streamed to a UDP port and the LEAD MPEG-2 Transport Source filter is used as the source filter.

   • These filenames use the syntax saic://*ip_address[/*network_card][:udp_port].

   • These streams require the LEAD MPEG-2 Transport Source and LEAD MPEG-2 Transport Decoder filters, which have special licensing requirements.

5. Filenames starting with "udp" are assumed to be streamed to a UDP port and the LEAD MPEG-2 Transport UDP Source filter is used as the source filter.

   • These filenames use the syntax udp://*ip_address[/*network_card][:udp_port][?param1=val1[¶m2=val2]].

   • These streams require the LEAD MPEG2 Transport UDP Source  and the LEAD MPEG2 Transport Demultiplexer.

6. Filenames starting with "tcp" are assumed to be streamed to a TCP/IP port and the LEAD MPEG-2 Transport UDP Source filter is used as the source filter.

   • These filenames use the syntax tcp://*ip_address*[:tcp_port][?param1=val1[¶m2=val2]].

   • These streams require the LEAD MPEG2 Transport UDP Source  and the LEAD MPEG2 Transport Demultiplexer.  

7. Filenames starting with "rtsp" are assumed to be streamed from an RTSP server and the LEAD RTSP Source filter is used as the source filter.

   • These filenames use the syntax rtsp://[username[:password]@]ip_address[:rtsp_port]/server_URL[?param1=val1[¶m2=val2]].

   • These streams require the LEAD RTSP Source.

8. Anything else is assumed to be a regular file and the regular DirectShow rendering mechanism is used.

Syntax for strings prefixed with ltsf:

Syntax for strings prefixed with saic and udp:

Syntax for strings prefixed with tcp:

Syntax for strings prefixed with rtsp:

Note 1: Parameters used to describe raw H264 video streams

H264 streams sent inside RTP packets use dynamic payloads with a payload type between 96 and 127. These streams can be decoded only when there is extra information being sent using a separate communication channel. The most common method of sending this extra information is through a Session Description Protocol (also known as SDP). The SDP contains extra information describing the stream. The UDP source needs to know the following information:

• the payload number and the compression associated with it

• the number of RTP units per second

• the sequence header information (if it is not sent with the video stream)

The UDP source needs to know this information in order to process these streams. There are two useful parameters right now (rtpmap and fmtp) and their syntax is described below:

• rtpmap=payload_type;compression/RTP_units_per_second

These values are usually sent in the SDP information via the a=rtpmap line, as in the following example:

a=rtpmap:99 H264/90000

This should be translated by replacing the space with semicolon (';) into

rtpmap=99;H264/90000

So, the URL syntax for a H264 stream sent to port 40000 containing RTP packets with a payload of 99 and with sequence header packets (NAL units 7 and 8) sent inside the compressed stream is something like this:

udp://192.168.1.100:40000?rtpmap=99;H264/90000

•  fmtp=payload_type;sprop-parameter-sets="seq1,seq2,...,seqN"

  
  

  Parameter	Description
  payload_type	The payload type. This value should be between 96 and 127. It should match the value in the rtpmap parameter.
  seqN	The base64 encoding of the sequence parameter. When there are several sequence headers, they are separated with a comma ( , ). Usually, there are two sequence headers. A double quote ( " ) should be added at the beginning and end of the sequence list.

Note that the three dots would not be passed in the string. They are there only to indicate there could be other seq values between seq2 and seqN.

These values are usually sent in the SDP information via the a=fmtp line, as in the following example:

a=fmtp:96 packetization-mode=1; profile-level-id=420029; sprop-parameter-sets=Z0IAKeKQFge2BqwYBBuHiRFQ,aM48gA==

In the above example, there are two sequence header strings following the sprop-parameter-sets, separated with a comma. The UDP source filter is interested only in the sprop-parameter-sets field, so this line should be translated into:

fmtp=96;sprop-parameter-sets="Z0IAKeKQFge2BqwYBBuHiRFQ,aM48gA=="

And this pair should be appended to the URL to form something like this:

udp://192.168.1.100:40000?rtpmap=99;H264/90000&fmtp=96;sprop-parameter-sets="Z0IAKeKQFge2BqwYBBuHiRFQ,aM48gA=="

The above URL syntax describes a stream streaming on port 40000, with H264 data inside RTP packets with payload type set to 99, with 90000 RTP units per second and whose sequence headers are not part of the stream. Instead, they are passed through the sprop-parameter-sets component of the fmtp parameter.

Note 2: Examples of RTSP Commands

RTSP servers are usually listening for commands to sent to a certain port. The commands can ask the server to describe the stream at a certain URL, to start, pause or stop playback.

In addition, certain servers allow the client to pass certain customization parameters to the server. These commands can change the compression used by the server, the video size, etc. These parameters are server-dependent and you should consult the server's documentation for information on the possible parameters supported by the server. You can see below an example of a command sent to a server to change the compression to jpeg. Again, keep in mind that this command might not work for another RTSP server.

Some RTSP Servers require the use of authentication to restrict access only to authorized users. In these cases, the RTSP Source Filter might display a login message box asking for a username and password. If you know the username and password beforehand, you can pass it as part of the URL to avoid having the message box appear. Note that the message box might still appear if the supplied username and/or password information is incorrect.

rtsp://192.168.0.164/axis-media/media.amp - Connect to an RTSP server running on 192.168.0.164 at the "axis-media/media.amp" URL. The data will be streamed using the default compression.

rtsp://root:pass@192.168.0.164/axis-media/media.amp?videocodec=jpeg - Connect to an RTSP server running on 192.168.0.164 at the "axis-media/media.amp" URL. The data will be streamed using JPEG compression. This server is using authentication, and we are connecting as username 'root' and with the password 'pass' in order to avoid having to enter the username and password.