Posts Tagged - gstreamer

AmLogic s805x GXL SoC board bring up

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:

Our developed Z8 board with AmLogic s805x SoC

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

# 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/
# 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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GStreamer H264/MP4 decoding C/C++ basics and encoding/decoding buffers manipulations

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:

gst-launch-1.0 filesrc location=/path/to/file.ogg ! decodebin ! alsasink
How to sink and src works

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

Another more complex example of playing an mp4 file:

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

gst_init (NULL, NULL);

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