Streaming GStreamer pipelines via HTTP

In the past many people joined the GStreamer IRC channel on FreeNode and were asking how to stream a GStreamer pipeline to multiple clients via HTTP. Just explaining how to do it and that it’s actually quite easy might not be that convincing, so here’s a small tool that does exactly that. I called it http-launch and you can get it from GitHub here.

Given a GStreamer pipeline in GstParse syntax (same as e.g. gst-launch), it will start an HTTP server on port 8080, will start the pipeline once the first client connects and then serves from a single pipeline all following clients with the data that it produces.

For example you could call it like this to stream a WebM stream:

Note that this is just a simple example of what you can do with GStreamer and not meant for production use. Something like gst-streaming-server would be better suited for that, especially once it gets support for HLS/DASH or similar protocols.

Now let’s walk through the most important parts of the code.

The HTTP server

First some short words about the HTTP server part. Instead of just using libsoup, I implemented a trivial HTTP server with GIO. Probably not 100% standards compliant or bug-free, but good enough for demonstration purposes :). Also this should be a good example of how the different network classes of GIO go together.

The HTTP server is based on a GSocketService, which listens on a specific port for new connections via a GLib main context, and notifies via a signal whenever there is a new connection. These new connections are provided as a GSocketConnection. These are line 424 and following, and line 240 and following.

In lines 240 and following we start polling the GIOStream of the connection, to be notified whenever new data can be read from the stream. Based on this non-blocking reading from the connection is implemented in line 188 and following. Something like this pattern for non-blocking reading/writing to a socket is also implemented in GStreamer’s GstRTSPConnection.

Here we trivially read data until a complete HTTP message is received (i.e. “\r\n\r\n” is detected in what we read), which is then parsed with the GLib string functions. Only GET and HEAD requests are handled in very simple ways. The GET request will then lead us to the code that connects this HTTP server with GStreamer.

Really, consider using libsoup if you want to implement an HTTP server or client!

The GStreamer pipeline

Now to the GStreamer part of this small application. The actual pipeline is, as explained above, passed via the commandline. This is then parsed and properly set up in line 362 and following. For this GstParse is used, which parses a pipeline string into a real GstBin.

As the pipeline string passed to http-launch must not contain a sink element but end in an element with the name “stream”, we’ll have to get this element now and add our own sink to the bin. We do this by getting the “stream” element via gst_bin_get_by_name(), setting up a GstGhostPad that proxies the source pad of it as a source pad of the bin, and then putting the bin created from the pipeline string and a sink element into a GstPipeline, where both (the bin and the sink) are then connected.

The sink we are using here is multisocketsink, which sends all data received to a set of aplication-provided GSockets. In line 390 and following we set up some properties on the sink that makes sure that newly connected clients start from a keyframe and that the buffering for all clients inside multisocketsink is handled in a sensible way. Instead of letting new clients wait for the next keyframe we could also explicitly request the pipeline to generate a new keyframe each time a client connects.

Now the last part missing is that whenever we successfully received a GET request from a client, we will stop handling any reads/writes from the socket ourselves and pass it to multisocketsink. This is done in line 146. From this point onwards the socket for this client is only handled by multisocketsink. Additionally we start the pipeline here for the first client that has successfully connected.

I hope this showed a bit how one of the lesser known GStreamer elements can be used to stream media to multiple clients, and that GStreamer provides building blocks for almost everything already 😉