Posts Tagged - gstreamer

One of the previous projects was related to bringing up our newly developed board with the AmLogic s805x SoC CPU board. I will describe how the proccess of bringing up looks like, what was tested and also we will take a look how the AmLogic board flashing proccess is carried out for GXL platform (G12B and more recent are very similar). This is our board:

The first stage of bringup is to build image for reference board. Our case is p241. We took a113 sources for this. Build p241 reference sources:

Build image

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# You need arm-linux-gnueabihf-gcc and aarch64-linux-gnu-gcc to be installed in system toolchains
$ sudo apt-get install zlib1g zlib1g-dev
$ source buildroot/build/setenv.sh
# Choose “mesongxl_p241_32_kernel49” // 37
$ ln -s aml-4.9 kernel/aml-3.14
$ ln -s aml-4.9 hardware/aml-3.14
$ make

After the proccess in complete everything will be at output/mesongxl_p241_32_kernel49/images with folowing parts:

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Exploring GStreamer and pipelines

Before proceeding to code review, let’s look at what we can do without it. GStreamer includes useful utilities to work with, in particular:

• gst-inspect-1.0 will allow you to see a list of available codecs and modules, so you can immediately see what will do with it and select a set of filters and codecs.
• gst-launch-1.0 allows you to start any pipeline. GStreamer uses a decoding scheme where a stream passes through different components in series, from source to sink output. You can choose anything as a source: a file, a device, the output (sink) also may be a file, a screen, network outputs, and protocols (like RTP).

Simple example of using gst-launch-1.0 to connect elements and play audio:

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gst-launch-1.0 filesrc location=/path/to/file.ogg ! decodebin ! alsasink

Filesrc will open file, decodebin - decode it, and alsasink will output audio.

Another more complex example of playing an mp4 file:

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gst-launch-1.0 filesrc location=file.mp4 ! qtdemux ! h264parse ! avdec_h264 ! videoconvert ! autovideosink

The input accepts the mp4 file, which goes through the mp4 demuxer — qtdemux, then through the h264 parser, then through the decoder, the converter, and finally, the output.

You can replace autovideosink with filesink with a file parameter and output the decoded stream directly to the file.

Programming an application with GStreamer C/C++ API. Let’s try to decode

Now when we know how to use gst-launch-1.0, we are doing the same thing within our application. The principle remains the same: we are building in a decoding pipeline, but now we are using the GStreamer library and glib-events.

We will consider a live example of H264 decoding.

Initialization of the GStreamer application takes place once with the help of

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gst_init (NULL, NULL);

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