Tvheadend

= Home Tv Streaming Protocol (HTSP) =

General

HTSP is a TCP based protocol primarily intended for streaming of live TV and related meta data such as channels, group of channels (called tags in HTSP) and electronic program guide (EPG) information.

The transmission and reception of a channel over HTSP is referred to a subscription. A single HTSP session can handle as many concurrent subscriptions as the bandwidth and CPU permits.

The HTSP server in tvheadend has a payload-aware scheduler for prioritizing more important packets (such as I-frames) before less important ones (such as B-frames). This makes HTSP is suitable for long-distance transmissions and/or paths with non-perfect delivery.
(It has been tested with a server in Stockholm and the client in Berlin).

The HTS Showtime client can be found [http://trac.lonelycoder.com/hts/browser/trunk/showtime/tv/htsp.c here].

----
Communication

This communication is currently implemented by using htsmsg:s. All strings are encoded as UTF-8.

There are two distinct ways for communication within HTSP.

Apart from this there is a number of messages that needs to be exchanged during login, see the login section below.

=== RPC communication ===

There is a normal RPC way of doing things. I.e. the client sends a request and the server responds with a reply. All the RPC methods are listed below as the 'Client to Server' methods. Apart from all message fields listed within each message type the client can add an additional field:

RPC request extra fields: {{{
seq int optional Sequence number. This field will be echoed back by the server in the reply.
username str optional Username, in combination with 'digest' this can be used to raise the privileges
for the session in combination with invocation of a method.
digest bin optional Used to raise privileges.
}}}

The followings field should be used by the client to match the reply with the request.
All replies are guaranteed to arrive in the same order as the requests.
Even so, probably the best way to implement the request-reply client is by taking advantage of the 'seq' field.

RPC reply extra fields: {{{
seq int optional Sequence number. Same as in the request.
error str optional If present an error has occurred and the text describes the error.
noaccess int optional If present and set to '1' the user is prohibited from invoking the method due to
access restrictions.
}}}

=== Streaming communication ===

For streaming of live TV and various related messages the server will continuously push data to the client.
These messages are referred to as asynchronous messages and always have the 'method' field set and never have the 'seq' field set.
Also, the client can enable an additional asyncMetadata mode and by doing so it will be notified by the server when meta data changes. (EPG updates, creation of channels and tags, etc).

=== Authentication ===

In Tvheadend, each method has an associated access restriction. Currently there is only one restriction (Streaming). However, this may change in the future.

Privileges for these restrictions may be granted in two ways: Username + Password and/or Source IP address.
Therefore it is possible to gain permissions to the system without entering a username and password.
While this is really useful it also complicates the authentication schema a bit.
Upon connect the initial privileges will be raised based on the source address.

Before any username / password based authentication has taken place the client must have
obtained a challenge (which stays fixed for the session). This is done via the 'hello' method.

In principle it's possible to use two different authentication idioms with HTSP.
Depending on how your application works one or another may be more suitable.
While they do not really differ from a protocol point of view it's worth mentioning a bit about them here:

=== Initial login authentication ===

The client performs all of its authentication using the 'login' method.

It may choose to send: * Username and password: Privileges will be raised based on these credentials. * Username only: Privileges will be based on just the source address. The username will be used for various logging purposes. * Nothing: Privileges will be based on just the source address.

If no privileges are granted after the login message has been received by the server (i.e. both network and username + password based)
the server will reply with 'noaccess' set to 1. A client that only employs initial login should honor this flag and ask the
user for a username + password and retry by using the 'authenticate' method. I.e. it should not send the 'login' method again.

=== On-demand authentication ===

The client performs all of its authentication when it needs to.

When using this method, the client will check every RPC reply for the 'noaccess' field.
If it set to 1 it whould ask the user for username + password and retry the request but also
add 'username' and 'digest' to the original message. (See ''RPC request extra fields'' above)

Typically it would not send a username or digest during login.

---

= Client to Server (RPC) methods =

---

=== hello ===

Used to identify the client toward the server and to get the session challenge used to
hash passwords into digests. The client can request a different version of the HTSP
protocol with this method. If no 'hello' message is sent the server assumes version 1
is to be used.

Request message fields: {{{
htspversion int required Client preferred HTSP version. If the server does not support this version
it will respond with an error and also set the 'invalidversion' field in the reply.
clientname str required Client software name.
clientversion str required Client software version.
}}}

Reply message fields: {{{
htspversion int required The server supports all versions of the protocol up to and including this number.
servername str required Server software name.
serverversion str required Server software version.
challenge bin required 32 bytes randomized data used to generate authentication digests
invalidversion int optional If set, this means that the server does not understand the requested version.
The 'error' field is also set to indicate an error.
}}}

---

=== authenticate ===

This can be used to issue authentication without doing anything else.
If no privileges are gained it will return with 'noaccess' set to 1.

Request message fields: {{{
None
}}}

Reply message fields: {{{
None
}}}

---

=== enableAsyncMetadata ===

When this is enabled the client will get continuous updates from the server about channels and tags.
This also includes creation and deletion of channels and tags.

An interactive application that presents the user with information about channels and tags would probably want to switch to this mode.

Request message fields: {{{
None
}}}

Reply message fields: {{{
None
}}}

---

=== getEvent ===

Request information about the given event. An event typically corresponds to a program on a channel.

Request message fields: {{{
eventId int required Event ID.
}}}

Reply message fields: {{{
start int required Start time of event (Seconds since the epoch, in UTC)
stop int required Ending time of event (Seconds since the epoch, in UTC)
title str required Title of event.
description str required Description of event. This can be quite huge and may also contain newlines.
nextEventId int optional ID of next event on the same channel.
}}}

---

=== subscribe ===

Request subscription to the given channel.

Request message fields: {{{
channelId int required ID for channel.
subscriptionId int required Subscription ID. Selected by client. This value is not interpreted by the server in any form.
The value is used from now on in all messages related to the subscription.
}}}

Reply message fields: {{{
None.
}}}

---

=== unsubscribe ===

Stop a subscription.
Attributes {{{
subscriptionId int required Subscription ID.
}}}

Reply message fields: {{{
None.
}}}

---

= Server to Client methods =

---

=== channelAdd ===

A new channel has been created on the server.

Message fields: {{{
channelId int required ID of channel.
channelName str required Name of channel.
channelIcon str required URL to an icon representative for the channel.
eventId int optional ID of the current (or next to be) event on this channel.
tags int[] optional Tags this channel is mapped to.
}}}

---

=== channelUpdate ===

A channel has been updated on the server. All fields will be sent even if they are not changed. Most clients can process this and the 'channelAdd' message
with the very same code.

Message fields: {{{
channelId int required ID of channel.
channelName str required Name of channel.
channelIcon str optioanl URL to an icon representative for the channel.
eventId int optional ID of the current (or next to be) event on this channel.
tags int[] required Tags this channel is mapped to.
}}}

---

=== channelDelete ===

A channel has been deleted on the server.

This message is only sent if session is in asynchronous mode.

Message fields: {{{
channelId int required ID of channel.
}}}

---

=== tagAdd ===

A new tag has been created on the server.

Message fields: {{{
tagId int required ID of tag.
tagName str required Name of tag.
tagIcon str optional URL to an icon representative for the channel.
channels int[] required Channels this tag is mapped to.
}}}

---

=== tagUpdate ===

A tag has been updated on the server.

Message fields: {{{
tagId int required ID of tag.
tagName str required Name of tag.
tagIcon str optional URL to an icon representative for the channel.
channels int[] required Channels this tag is mapped to.
}}}

---

=== tagDelete ===

A tag has been deleted from the server.

Message fields: {{{
tagId str required ID of tag.
}}}

---

=== initialSyncCompleted ===

Sent after all the initial channel and tag messages has been sent when session has been set to async mode.

Added in HTSP version 2.

Message fields: {{{
}}}

---

=== subscriptionStart ===

Message fields: {{{
subscriptionId int required Subscription ID.
streams msg[] required Array of messages with stream information
source str optional Textual representation of the source
network str optional Network (more detailed description of source). Typically this is the DVB network.

'streams' message:

index int required Index for this stream
type str required Type of stream
language str optional Language for stream

Stream types:
AC3 AC3 audio
MPEG2AUDIO MPEG2 audio (MP2)
MPEG2VIDEO MPEG2 video
H264 H264 video
AAC ADTS framed AAC (one AAC packet per ADTS frame)
}}}

---

=== subscriptionStop ===

Message fields: {{{
subscriptionId int required Subscription ID.
reason str optional Reason for subscription stop.
}}}

---

=== subscriptionStatus ===

Message fields: {{{
subscriptionId int required Subscription ID.
status str optional English clear text of error status. Absence of this field means that the status is OK.
}}}

---

=== queueStatus ===

The queueStatus message is sent every second during normal data delivery.

The transmit scheduler have different drop thresholds for different frame types.
If congestion occurs it will favor dropping B-frames before P-frames before I-frames.
All audio is recognized as I-frames.

Message fields: {{{
subscriptionId int required Subscription ID.
packets int required Number of data packets in queue.
bytes int required Number of bytes in queue.
delay int required Estimated delay of queue (in µs)
Bdrops int required Number of B-frames dropped
Pdrops int required Number of P-frames dropped
Idrops int required Number of I-frames dropped
}}}

---

=== muxpkt ===

Streaming data.

Message fields: {{{
subscriptionId int required Subscription ID.
frametype int required Type of frame as ASCII value: 'I', 'P', 'B'
stream int required Stream index. Corresponds to the streams reported in the subscriptionStart message.
dts int required Decode Time Stamp in µs.
pts int required Presentation Time Stamp in µs.
duration int required Duration of frame in µs.
payload bin required Actual frame data.

}}}