= WebGL Extension Proposal =

Byungseon Shin, LG

== Motivations ==

* YouTube on TV HTML5
    * YouTube 360 does not play at smooth 60FPS on embedded devices
* WebGL for 360-degree video.
* Must support VideoElement source
* Should render smoothly (~60 fps)
     * Most of the GPU resources are consumed by Color Space Conversion (CSC) processing


== VR Technology ==

* 360 VR Tech: spherical mapping of equirectangular textures
* Maping a flat surface onto a 3D model (in this case, a sphere).
* Equirectanular Format: -- A bit like a map projection.
* Native OpenGL ES implementation was 60 fps. Video -> libvt - { texture } -> Sphere Mapping (OpenGL) -> Frame Buffer.
* Initially tried WebGL, but was SLOW. (~30 fps). Video -> libvt - { texture } -> WebGL (YUV -> RGBA) -> Sphere Mappig (OpenGL) -> Frame Buffer.
    * There's an extra step of converting from libvt to RGBA
    * In the case of 360VR, final screen size will be far smaller than input screen, but we have to convert full screen to use WebGL
    * Three bottlenecks:
        * Color Space Conversion (YUV -> RGB): 90%
        * Texture Copy inside Video Decoder: 8-9%
        * Compositing of WebGL canvas: 1-2%

* Currently WebGL only supports TEXTURE_2D (RGBA) as an import. Not YUV.
* YUV -> RGB conversion is very slow.

== Proposal ==

=== OES_EGL_image_external ===

* Add an OES_EGL_image_external extension on WebGL. -- Allows YUV textures to be handled without color space conversion.
* Solution: currently, WebGL only supports TEXTURE_2D (RGBA). We should make it support TEXTURE_EXTERNAL_OES as well
* Expose OES_EGL_image_external functionality to WebGL (define a new texture target TEXTURE_EXTERNAL_OES)
* Advantage over existing proposals: focus on extending texture format of WebGL. Make it easy to port and use
* 2 issues pointed out in the WG:
    * EGL image sync issue (syncing EGL image between video decoder)
    * Audio sync (need exact timestamp of the frame currently being rendered)
* Also need other per-frame metadata like dimensions of the texture
* This approach allows avoiding converting the entire video image from YUV -> RGBA. Instead, only need to decode the region presented in the frame buffer.
* This extension already exists in OpenGL. This is just a matter of exposing through WebGL.
* Some competing proposals work on a similar problem, but are not as good a fit

== Challenges ==

* Audio sync is a key challenge to overcome.

== Questions ==

* Why not just decode the portion of the image that will be displayed?
    * Might work if the viewport is fixed, but this won't have optimal performance when changing the viewport