gstreamer/gst/audiovisualizers

A basclass for audiovisualizers. Takes care of re-fitting the audio-rate to
video-rate. It receives audio-data at the sampling-rate. It needs to render
video-frames at frame-rate. The rendering needs n audio samples (depends on
subclass). The baseclass takes care of that.

Some effects could be enhanced by running geometrictransform/effecttc elements
afterwards.

= Feedback =
* put 'Audio' to klass as well ?

= API =

* we have a couple of drawing helpers in gstdrawhelpers.h
  (would be nice if we could use cairo) 
  draw_point (x,y,color);
  draw_line (x1,x2,y1,y2,color);
* some more we could add:
  draw_hline (x1,x2,y,color);
  draw_vline (x,y1,y2,color);
  draw_rect (x1,x2,y1,y2,color);
  draw_box (x1,x2,y1,y2,color); // filled
* shading effects
  - would be nice to use a generic 3x3 matrix operation, we don't run inplace
    anyway
  - this way we could also blur the background

= Elements to port =
gst-plugin-ugly/gst/synaestesia -> synaescope
gst-plugin-bad/gst/smoothwave -> wavescope
gst-plugin-good/gst/monoscope -> blend into what we have in wavescope

= Elements to add =
spectrascope - done
spacescope - stereo wavescope
- left->x, right->y - done
- polar mapping
wavescope
- we could have a bouncing line as a base, like a quix:
  - two dots moving on a linear path and getting a new random dx,dy when hitting
    a border
  - the abs(dx/dy) - speed of movement - could be scaled by the sound level
  - we would need to rotate, stretch and clip the waveform drawing to fit the
    line
  - we could scratch the rotate part and just stretch/squeeze x and shift/clip y

xxxscope
- have a matrix of source and drawing-functions
  - sources: audio, spectrum, audio-low, audio-mid, audio-hi
  - drawing: waves (style, color), space (style,color)
- have the usual shade and move operations
- have a way to draw each operator in one or more color-channels
- we could calculate the sound-level (like in level element) and modulate
  colors/movements
  - for filtered low/mid/hi audio we could use different peak-falloffs

= TODO =
- element maker template
- test for baseclass

- we probably want a VisBin like the gnome video effects
- this way we can specify pipeline fragments
- VisBin can use a videomixer to switch effects based on time or song
- VisBin can e.g. control a text-overlay to render the title into the 
  visualisation for a while

= Test it =

GST_DEBUG="*:2,*scope*:4"

GST_PLUGIN_PATH=$GST_PLUGIN_PATH:$PWD gst-inspect scopes

GST_PLUGIN_PATH=$GST_PLUGIN_PATH:$PWD gst-launch audiotestsrc ! audioconvert ! wavescope ! colorspace ! ximagesink
GST_PLUGIN_PATH=$GST_PLUGIN_PATH:$PWD gst-launch filesrc location=$HOME/Music/1.mp3 ! decodebin2 ! audioconvert ! wavescope ! colorspace ! ximagesink
GST_PLUGIN_PATH=$GST_PLUGIN_PATH:$PWD gst-launch filesrc location=$HOME/Music/1.mp3 ! decodebin2 ! audioconvert ! wavescope style=lines shade-amount=0x00080402 ! edgetv ! vertigotv ! ximagesink

GST_PLUGIN_PATH=$GST_PLUGIN_PATH:$PWD gst-launch filesrc location=$HOME/Music/1.mp3 ! decodebin2 ! audioconvert ! spacescope style=lines shade-amount=0x00080402 ! ximagesink
GST_PLUGIN_PATH=$GST_PLUGIN_PATH:$PWD gst-launch filesrc location=$HOME/Music/1.mp3 ! decodebin2 ! audioconvert ! spacescope style=lines shade-amount=0x00080402 ! vertigotv ! ximagesink

GST_PLUGIN_PATH=$GST_PLUGIN_PATH:$PWD gst-launch filesrc location=$HOME/Music/1.mp3 ! decodebin2 ! audioconvert ! spectrascope ! colorspace ! ximagesink
GST_PLUGIN_PATH=$GST_PLUGIN_PATH:$PWD gst-launch filesrc location=$HOME/Music/1.mp3 ! decodebin2 ! audioconvert ! spectrascope shader=fade-and-move-up shade-amount=0x00040302 ! colorspace ! ximagesink

GST_PLUGIN_PATH=$GST_PLUGIN_PATH:$PWD gst-launch filesrc location=$HOME/Music/1.mp3 ! decodebin2 ! tee name=t ! queue ! audioconvert ! synaesthesia ! ximagesink t. ! queue ! synaescope shade-amount=0x00040404 ! colorspace ! ximagesink