Chapter 1. VLS overview
- Table of Contents
- VLS design
- General architecture
- Common classes overview
VLS design
The VideoLAN Server is programmed in C++, with an entirely "hand-made" framework. It means that VLS does not (and will not) use Standard Template Library classes such as iostreams or vectors. The internal VLS framework is supposed to be complete enough, so nothing should have to be written any more (except maybe for porting VLS to other operating systems).
VLS is made up of three parts: a framework (located in src/core), common classes (in src/server and src/mpeg) and optional classes called modules (in src/modules). Modules are actually classes inherited from common classes. Some classes that are considered as common classes at the moment may become modules in the future.
General architecture
The general architecture of the VLS is shows on the diagram below :
We can isolate 3 main parts : the source thread (Reader and MpegConverter), the consumer thread (TsStreamer and the Output) and the Management part (Input, Admin and Manager).
The Management part spawns all the needed parts and modules, when the Vls is strarted or when a new stream is started.
The source thread reads the data through the reader as fast as possible to fill up the SyncFifo.
Then, the consumer thread gets the packets from the SyncFifo and stream them. The timing of this streaming is managed by the TsStreamer, which give them the Output module. The m_cFifo of TS_IN_ETHER packet length is used to gather several TS Packets before sending them together in one UDP packet (for the NetOutput module).
To improve the efficiency and avoid too many memory allocations, a pool of TS Packet is allocated once : it is the TsProvider. That means that at the beginning of the chain, a new TsPacket is called by the Converter (TsProvider->GetPacket()), filled up with bytes from the reader, goes through the TsStreamer and the Output. After being send, the TsPacket is reset available in the TsProvider (TsProvider->ReleasePacket()).
The size of the TsProvider is calculated to be able to handle about 3 seconds of stream.
Common classes overview
Here is an overview of some common classes present in VLS (be careful: a class drawn within another one is a member of that class, not a child) :
- C_Vls
It is the main class of the VideoLAN Server. Its role is to load modules, launch the Admin and the Manager, and forward messages between them.
- C_Admin
It is the main administration class, whose role is to control the various administration interfaces, and to parse and handle the commands sent to these interfaces.
- C_Telnet
This is the telnet administration interface, the only one supported at the moment.
- C_Manager
The Manager is one of the most important classes of VLS. It launches the various inputs and channels according to the configuration file vls.cfg, contains a list of all the available programs and a list of the currently broadcasted programs. It is this class which interprets the commands sent to the Admin, and can tell inputs to start, stop, suspend or resume streams.
- C_Channel
This is the parent class of all the channel (i.e. output) modules. Currently implemented channels are network and file.
- C_PgrmDirectory
It is the list of all the programs available in the various inputs.
- C_Broadcast
A "broadcast" is defined by an input/program/channel combination. It represents a stream that is currently broadcasted by VLS.
- C_Input
This is the parent class of all the input modules. An input basically gets a MPEG stream from a source (thanks to a "reader") and sends it to a converter. Each input contains a list of the available programs it can provide.
- C_MpegReader
An MpegReader reads data from a source (file, DVD, ...) and delivers a continuous MPEG (PS or TS) stream.
- C_MpegConverter
An MpegConverter converts the stream provided by the Reader into a valid MPEG-TS stream.
- C_TsStreamer
The Streamer reads data from a Converter and sends it to a Channel at the right speed.