Matroska Server Mk2

This project is the result of years of thinking, trying and finally succeeding.

This software makes it possible to stream (almost) anything remuxed as matroska live in real-time over http to multiple clients.

This is probably also one of the first real world usages of FFmpeg's http server component (which I wrote as part of GSoC 2015).

The second sentence basically said everything already, so let's dive into some usage examples:

First of all, clone the repo and try to build the project:

[email protected]~$ make

If successful you will have built the server binary. Let's get some files to stream!

[email protected]~$ ./server somevideo.mkv

This will serve the file somevideo.mkv on all interfaces on port 8080 (so far only configurable in server2.c) in real-time.

You can also use stdin from a live feed for example:

[email protected]~$ wget http://example.org/livestream -O - | ./server

Or just read it directly as an http served file:

[email protected]~$ ./server http://example.org/livestream

Or you can have an easy screencasting setup:

On a server:

[email protected]~$ nc -l -p 12345 | ./server

On a client:

[email protected]~$ ffmpeg -f x11grab -framerate 15 -s 1920x1080 -i :0.0 -c:v libx264 -f matroska tcp://remote:12345

You will see the server writing some information, as it is still quite verbose (it was even more verbose in earlier versions for obvious reasons ;) ).

Architecture

With the latest iteration more sophisticated data structures have been used. The following structs make up the architecture:

Segment

Contains a segment of data. A segment is always exactly one GOP, that implies segments always start at a keyframe. Segments are refcounted.

BufferContext

Circular buffer that manages segments and takes care of refcounting them.

PublisherContext

Holds a BufferContext for new segments and a BufferContext for old segments that should still be sent to new clients. This makes streams on clients start faster and stutter less.

Also holds a list of Clients, which in turn have a BufferContext of segments that still have to be sent to the client.

When the server receives a file (through stdin or by specifying a file), the Publisher receives them as Segments. That means the Segment has to be read completely before it can be served to clients. Once it is in the Publisher's Buffer, it will be sent to clients. Additionally the Publisher keeps a number of Segments (publisher.h:BUFFER_SEGMENTS) that will be sent to any client that connects. These Segments are the last Segments received. This was added to prevent players from hanging if the video being streamed has very different GOP sizes. To fill this Buffer, the server reads the first BUFFER_SECS (server2.c) of the file regardless of timestamp information in the file.

Effectively this means that if BUFFER_SEGMENTS is set to 0, there will still be at least a delay of one GOP. This constraint made implementation a lot safer as Segments are never written and read at the same time. Therefore in order to reduce latency, this constant should be defined to 0 and the keyframe-interval of the file should be short.

Dependencies

• recent ffmpeg libraries

(optional) git-format patches are in the "patches/" directory.

Todo

• Argument parsing
• Configuration
• Documentation
• Management interface
• Low-latency mode?

Known issues

• still leaks very small amounts of memory (valgrind reports a few thousand bytes)

Thanks

• Clément Bœsch <ubitux> for kind of "triggering" this project with a bugreport
• Nicolas George for mentoring me during GSoC. I would never be familiar enough with the codebase without him and the project.