[Mplayer-cvslog] CVS: main/DOCS/tech libvo2.txt,NONE,1.1

[Arpi of Ize]

Update of /cvsroot/mplayer/main/DOCS/tech
In directory mplayer:/var/tmp.root/cvs-serv14716

Added Files:
	libvo2.txt 
Log Message:
libvo2 draft by Ivan - with linewrapping...

--- NEW FILE ---
This is a brief description on libvo2 interface. It is not C code, just
draft scheme. Feel free to suggest exact parameters.
I have tried to put some numbering. So if you want to reply then put the 
topic number in the subject line. Please don't reply to the whole draft, 
or at least don't include big paragraphs from it.
I'm gonna put this text as attachment to force you to copy only the parts 
you want to reply;)

   Best Regards
Ivan Kalvachev

1.libvo2 drivers 
1.1 functions
Currently these functions are implemented:
  init
  control
  start
  stop
  get_surface
  flip_image

They are simple enough. So I introduce to be implemented and these functions:
  query
  update_surface - renamed draw
  hw_decode
  subpicture

Here is detailed description of new functions:

  query - the negotiation is more complex than just finding which imgfmt the
  device could show, we must have list of capabilities, testing modes, etc.
  this function will have at least 3 modes:

    a) return list of available modes with description.
    b) check could we use this mode with these parameter. E.g. if we want
       RGB32 with 3 surfaces for windows image 800x600 we may get out of video
       memory. We don't want error because this mode could be used with 2
       surfaces.
    c) return supported subpicture formats if any.

As you may see I have removed some functionality from control() and made
separate function. Why? It is generally good thing functions that are
critical to the driver to have it's own implementation.

  update_surface - as in the note above, this is draw function. Why I change
    it's name? I have 2 reasons, first I don't want implementation like vo1,
    second it really must update video surface, it must directly call the
    system function that will do it. This function should work only with
    slices, the size of slice should not be limited and should be passed (e.g
    ystart, yend), if we want draw function, we will call one form libvo2
    core, that will call this one with start=0; ymax=Ymax;. Also some system
    screen update functions wait for vertical retrace before return, other
    functions just can't handle partial updates. In this case we should inform
    libvo2 core that device cannot slice, and libvo2 core must take care of
    the additional buffering.

  hw_decode - to make all dvb,dxr3, tv etc. developers happy. This function
    is for you. Be careful, don't OBSEBE it, think and for the future, this
    function should have and ability to control HW IDCT, MC that one day will
    be supported and under linux. Be careful:)

  subpicture - this function will place subtitles. It must be called once to
    place them and once to remove them, it should not be called on every
    frame, the driver will take care of this.  Currently I propose this
    implementation: we get array of bitmaps. Each one have its own starting
    x, y and it's own height and width, each one (or all together) could be
    in specific imgfmt (spfmt). THE BITMAPS SHOULD NOT OVERLAP! This may not
    be hw limitation but sw subtitles may get confused if they work as 'c'
    filter (look my libvo2 core).
    
1.2 control()
OK, here is list of some control()s that I think that could be useful:
    SET_ASPECT
    SET_SCALLE_X, SET_SIZE_X
    SET_SCALLE_Y, SET_SIZE_Y
    RESET_SIZE
    GET/SET_POSITION_X
    GET/SET_POSTIION_Y
    GET/SET_RESOLUTION
    GET/SET_DISPLAY
    GET/SET_ATTRIBUTES

Here is description of how these controls to be used:

  SET_ASPECT - this is the move/video aspect, why not calculate it in
  different place (mplayer.c) and pass the results to driver by
  set_size_x/y. First this is only if hardware could scale. Second we may
  need this value if we have TV and we won't calculate new height and width.

  SET_SCALLE_X/Y - this is to enlarge/downscale  the image, it WILL NOT
  override SET_ASPECT, they will have cumulative effect, this could be used
  for deinterlacing (HALF SIZE). Second if we want to zoom 200% we don't
  want to lose aspect calculations. Or better SET_SCALLE to work with
  current size?

  SET_SIZE_X/Y - This is for custom enlarge, to save some scale calculation
  and for more precise results.

  RESET_SIZE - Set the original size of image, we must call SET_ASPECT agein.

  GET/SET_POSOTION_X/Y - This if for windows only, to allow custom move on
  window.

  GET/SET_RESOLUTION - change resolution and/or bpp if possible. To be used
  for window or if we want to change the given resolution of the current
  fullscreen mode (NOT TO SET IT just to change it if we don't like it)

  GET/SET_DISPLAY - mainly for X11 and remote displays. Not very useful, but
  may be handy.

  GET/SET_ATTRIBUTES - Xv overlays have contrast, brightness, hue,
  saturation etc. these and others could be controlled by this. If we want
  to query it we must call GET_*, and the to check does our attribute is in
  there (xv developers be careful, 2 or 3 of default attributes sometimes
  are not queried by X, but could be set).

Do you think that TV encodings (NTSC,PAL,SECAM) should have it's own attribute?
I would like to hear the GUI developers. Could we separate Mouse/Keyboard
from the driver. What info do you need to do it. Don't forget that SDL have
it's own keyboard/mouse interface. Maybe we should allow video driver to
change the libin driver ?

1.3. query()

Here come and some attributes for the queried modes, each supported mode
should have such description. It is even possible to have more than one mode
that could display given imgfmt.

{ Scale y/n - hardware scale, do you think that we mast have one for x and
  one for y (win does)?

  Fullscreen y/n - if the supported mode is fullscreen, if we have yv12 for
fullscreen and window we must threat them as separate modes. Window y/n -
same as Fullscreen.

  GetSurface y/n - if driver could give us video surface we'll use get_surface()

  UpdateSurfece y/n - if driver will update video surface through sys function (X,SDL)

  HWdecode y/n  - if driver could take advantage of hw_decode()

  MaxSurfaces 1..n - Theoretical maximum of surfaces

  SubPicture y/n - Could we put subpicture (OSD) of any kind by hw

  WriteCombine y/n - if GetSurface==yes, most (or all) pci&agp cards are
  extremely slow on byte access, this is hint to vo2 core those surfaces
  that got affected by WC. This is only a hint.

  us_clip y/n - if UpdateSurface=yes, this shows could update_surface()
  remove strides (when stride> width ), this is used and for cropping. If
  not, we must do it.

  us_slice y/n - if UpdateSurface=yes, this shows that after executing
  update_surface(), the function won't wait for vertical retrace, and we
  could update surface slice by slice. If us_slice=0 we will have to
  accumulate all slices in one buffer.

  us_upsidedown - if UpdateSufrace=yes, this shows that update_suface()
  could flip the image vertically. In some case this could be united with
  us_clip /stride game/

  switch_resoliton y/n - if window=y, this shows could we switch resolution
  of desktop, if fullscreen=y, shows that we could change resolution, after
  we have set the fullscreen mode.

  deinterlace y/n - indicates that the device could deinterlace on it's own
  (radeon, TV).

1.4 conclusion 

As you see, I have removed all additional buffering from the driver. There
is a lot of functionality should be checked and handled by libvo2 core.
First we should check what else could be added to this draft. Then to check
all cases and how to handle them. Some of the parameters should be able to
be overriden by user config, mainly to disable buggy modes or parameters. I
belive that this should not be done by command line as there are enough
commands now.

//---------------------------
2. libvo2 core
2.1 functions
now these function are implemented:
    init
    new
    start
    query_format
    close

and as draw.c:
    choose_buffering
    draw_slice_start
    draw_slice
    draw_frame
    flip

init() is called at mplayer start. internal initialisation.
new() -> rename to open_drv() or something like this.
query_format -> not usable in this form, this function mean that all
  negotiation will be performed outside libvo2. Replace or find better name.
close -> open/close :)

choose_buffering - all buffering must stay hidden. The only exception is for
  hw_decode. In the new implementation this functions is not usable.
draw_slice_start, draw_slice -> if you like it this way, then it's OK.
draw_frame -> classic draw function.

2.2 Minimal buffering

I should say that I stand after the idea all buffering, postprocessing,
format conversion , sw draw of subtitles, etc to be done in libvo2 core.
Why? First this is the only way we could fully control buffering and
decrease it to minimum. Less buffers means less coping. In some cases this
could have the opposite effect (mpeg2 with internal buffers in video memory
without HW IDCT, MC, or if we have unaligned write).

The first step of the analyse is to find out what we need:

DECODER   -   type_of_buffer:{internal/static/normal}, 
              slice:{not/supported}

FILTER 1..x - processing:{ c-copy(buff1,buff2), p-process(buff1) }, 
              slice:{not/supported}
              write_combine:{not/safe}, 
              runtime_remove:{static/dynamic}

VIDEO_OUT  -  method:{get_surface/update_surface}, 
              slice:{not/supported}, 
              write_combine:{not/safe},
              clip:{can/not},
              upsidedown:(can/not),
              surfaces:{1/2/3,..,n}

  If we want direct rendering we need normal buffer, no filters, and (at
  least) 2 video surfaces. (we may allow 'p' filter like subtitles).

  If we have static buffer, we have 2 choices: to render in 1 surface
  (visual flickering) or to make additional buffering and draw on flip_page
  (like in libvo1).

Here I introduce and one letter codes that I use for analyse.
Details: 

DECODER - We always get buffer from the decoder, some decoders could give
  pointer to it's internal buffers, other takes pointers to buffers where
  they should store the final image. Some decoders could call draw_slice
  after they have finished with some portion of the image.

  type_of_buffer - I take this from the current libvo2 spec.  I call 'I'
  internal buffer (readonly), 'K' static buffer(one,constant pointer), and
  'B' - normal buffer.

  slice - this flag shows that decoder knows and want to work with slices.

FILTER - postprocessing, sw drawing subtitles, format conversion, crop,
additional filters.

  slice - could this filter work with slice order. We could use slice even
  when decoder does not support slice, we just need 2 or more filters that
  does. This could give us remarkable speed boost.

  processing - some filters can copy the image from one buffer to the other,
  I call them 'c', convert and crop(stride copy) are good examples but don't
  forget simple 1:1 copy. Other filters does process only part if the image,
  and could reuse the given buffer, e.g. putting subtitles. Other filters
  could work in one buffer, but could work and with 2, I call them 't'
  class, after analyse they will fade to 'c' or 'p'.

  runtime_remove - postprocess with autoq. Subtitles appear and disappear,
  should we copy image from one buffer to another if there is no processing
  at all?

//clip, crop, upsidedown - all 'c' filters must support strides, and should
  be able to remove them and to make some tricks like crop and upside_down.

VIDEO_OUT - take a look of libvo2 driver I propose.
  method - If we get surface -'S'. If we use draw* (update_surface) - 'd'

As you may see hd_decode don't have complicated buffering:)
I make the analyse this way. First I put decoder buffer, then I put all
filters, that may be needed, and finally I put video out method.

2.3. Rules for minimal buffering
The rules are these: 
The 'p' filters process in the buffer of the left, if we have 'I' buffer
then insert copy and new 'B' buffer.
With 'c' filter we must make sure that we have buffer ('B' or 'S') from the right(->) side. 
We must take care that, if we have S we need to finish with copy ('c'), and
if we have 'd' we must end with some kind of buffer.
In the usual case 't' are replaced with 'p' except when 't' is before 'S'.
If we have 'B S' or 'K S' we may make direct rendering and remove the 'B' or 'K' buffer.
We must have at least one 'c' if we have to make crop, clip, or flip image upside down.
Take care for the additional buffering when we have 1 surface (the libvo1 way).
Be aware that some filters must be before other. E.g. Postporcessing should
be before subtitles:)
If we want scale (-zoom), and vo2 driver can't make it then add and scale
filter 'c'. For better understanding I have one convert filter that can
copy, convert, convert and scale. The only thing that is missing now is
simple scale (yv12).

I have made grammar for these cases but it is too big and I hope that
something cleverer could be made. Don't think that having only 3 filters
(postporcess, convert/copy, subtitles) may make the things simpler. This
algorithm could be used and for numerous filters used in encoders.

2.4 Negotiation
Few words about negotiation. It is hard thing to find the best mode. Here is
algorithm that could find the best mode. But first I must say that we need
some kind of weight for the filters and drawing. I think that we could use
something like megabytes/second, something that we may measure or benchmark.

  1. We choose codec
  2. We choose video driver.
  3. For each combination find the total weight and if there are any
  optional filters find min and max weight. Be careful max weight is not
  always at maximum filters!!
  4. Compare the results.

I may say that we don't need automatic codec selection as now we could put
best codecs at beginning of codecs.conf as it is now. We may need to make
same thing with videodrv.conf :)