Enable h264 and ffmpeg support on YARP in the superbuild?

[traversaro]

In the near future, the following carrier and portmonitors may be useful for people working on video streams (@nunoguedelha @S-Dafarra @prashanthr05 just to mention a few):

• ffmpeg_grabber and ffmpeg_writer devices (depends on ffmpeg)
• h264 carrier (depends on gstreamer and ffmpeg)
• image_compression_ffmpeg portmonitor (depends on ffmpeg)

Ideally I would like to avoid adding more options to the superbuild to simplify the life of people (more options increase the possibility of getting options wrong). However, at this point I start being a bit afraid of dependency size. On apt systems, this new options will require to install the following dependencies:

libgstreamer1.0-dev
libgstreamer-plugins-base1.0-dev
gstreamer1.0-plugins-base (for videoconvert and appsink)
gstreamer1.0-plugins-good (for udpsrc and rtph264depay)
gstreamer1.0-plugins-bad (for h264parse)
gstreamer1.0-libav (for avdec_h264)
libavcodec-dev 
libavdevice-dev
libavfilter-dev
libavformat-dev
libavutil-dev
libpostproc-dev
libswresample-dev
libswscale-dev

some dependencies (ffmpeg) are already opencv dependendecies so we are already installing them, but a quick check reveals that on the top of an existing superbuild installation these dependencies add:

61.3 MB of additional disk space will be used

@Nicogene @vtikha @xEnVrE do you think that this additional used space is problematic? I am particularly curious to understand if this could be a problem for Docker or can/pc104 robots.

[traversaro]

Installing only ffmpeg just install 6 Mb more, so probably we could proceed at least with that.

[traversaro]

xref: robotology/yarp#2885