Written by: Sascha Volkenandt <sascha@akv-soft.de>
Project's homepage: http://www.magoa.net/linux/
Version: 0.0.3
Description:
------------
I call this protocol "VTP", the Video Transfer Protocol. I hope that's not
already claimed by someone ;).
This Protocol was created for Video Transfers over a Network. It is a text-
based protocol like the FTP, and is used by a client to communicate with a
server providing different types of video data, such as live streams,
recordings or disc media. The basic communication consists of short text
commands sent by the client, answered by numerical codes accompanied by
human-readable messages. All messages should be finished by a full CR/LF
line-ending, which should preferably written as "\015\012", as this is fully
platform-independent. Nevertheless, a client or (especially) a server should
also act on "\n" line-endings. The MPEG data is being transmitted over a
separate data connection.
TODO:
- PORT behaviour changed
- TUNE syntax changed
- connection IDs
- new command PLAY
Response Code Summary
Code Meaning
220 Last command ok / connection ready
221 Service is closing the connection afterwards
500 The command was not recognized
501 The parameters couldn't be interpreted correctly
550 Action not taken, for various reason
551 Action not taken, a subsequent connection was unsuccessful
560 Live-Stream not available currently [changed in 0.0.3]
561 Capability not known [new in 0.0.2]
562 Pid currently not available [new in 0.0.3]
563 Stream not available currently [new in 0.0.3]
Command Reference
Command: Connect to VTP Server
Responses: 220 - The server is ready
Description: Upon connection to the server (which usually listens at port
2004), the first thing the client has to expect is a welcome message with
the "220" response code. The client may now send a CAPS command, to tell
the server it's capabilities.
Command: CAPS <Capability>
Responses: 220 - This capability is known and will be used from now on.
561 - This capability is unknown, try anotherone
Description: This command tells the server to serve media data in a specific
format, like "PES" (for MPEG2-PES) or "TS" (for MPEG2-TS). A client can
do several CAPS commands until the server accepts one. So a client should
try all formats it can handle, descending from the most preffered one. If
no such command is sent, streaming is defaulted to PES.
Capabilities currently used:
TS Transport Stream (all PIDs belonging to a channel)
TSPIDS Only in conjunction with TS: Stream PIDs separately upon request
(this enables the ADDP/DELP commands)
PES Program Elementary stream (Video and primary Audio stream)
[new in 0.0.2,updated in 0.0.3]
Command: PROV <Priority> <Media>
Responses: 220 - Media available for receive
501 - The parameters were incorrect
550 - The media couldn't be identified
560 - This server can currently not serve that media
Description: With this command, the server is asked if the given media can
be received. The Priority is a number between 0 and 100 (in case a media
can not be received by an unlimited number of clients, the server shall
grant higher priorities before lower ones, and it shall also quit streams
with lower permissions if a higher one is requested), or -1 to ask the
server if this media is available at all.
The Media is a string defining the wanted media type. This is currently for
free use, it could for example carry a VDR unique channel id, to specify
a TV channel.
Command: PORT <Id> <Address and Port>
Responses: 220 - The data connection was opened
501 - The parameter list was wrong
551 - The data connection was refused by the client or timed out
Description: The PORT command tells the server the target of a following
media transmission. The parameter Id specifies an index which is used to
establish multiple data connections over one control connection. It is used
later in the ABRT command to close a specific data connection. The second
parameter argument has six comma-separated fields, of which the first four
represent the target IP address, in the byte-order as the dot-notation
would be printed. The last two fields represent the target port, with the
high-byte first. To calculate the actual values, you could use the
following:
Field(5) = (RealPort & 0xFF00) shr 8
Field(6) = RealPort & 0xFF
Reversed:
RealPort = (Field(5) shl 8) + Field(6)
After receiving the port command, the data connection is opened but no data
is transferred, yet.
Id's currently used:
0 Data connection for live streams
1 Data connection for saved streams
[changed in 0.0.3]
Command: TUNE <Priority> <Media>
Responses: 220 - Data connection was opened successfully
550 - The media couldn't be identified
560 - The live stream is unavailable
Description: This command tells the media server to start the transfer over a
connection to a remote target established by the PORT command before.
Please look at the PROV command for the meaning of the parameters. The
server begins to send MPEG data. After the transfer has been started, the
response code "220" is sent.
Command: ADDP <Pid>
Responses: 220 - The requested Pid is transferring
560 - The requested Pid is not available currently
Description: This tells the server to start the transfer of a specific Pid
over a data connection established by the PORT command before.
Command: DELP <Pid>
Responses: 220 - The requested Pid is transferring
560 - The requested Pid was not transferring
Description: This tells the server to stop the transfer of a specific Pid
enabled by DELP before.
Command: ABRT <Id>
Responses: 220 - Data connection closed
Description: This one should be sent before requesting another media or when
a media isn't needed anymore. It terminates the data connection previously
opened by PORT.
Command: QUIT
Responses: 221 - Connection is being closed afterwards
Description: This commands terminates the client connection.
