mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-20 00:31:13 +00:00
design: Add a proposal for handling stereoscopic 3D and multiview
This commit is contained in:
Jan Schmidt
parent
9297fe9ba0
commit
e35cf63216
1 changed files with 175 additions and 0 deletions
175
docs/design/part-stereo-multiview-video.markdown
Normal file
175
docs/design/part-stereo-multiview-video.markdown
Normal file
|
|
@ -0,0 +1,175 @@
|
|||
Design for Stereoscopic & Multiview Video Handling
|
||||
==================================================
|
||||
|
||||
There are two cases to handle:
|
||||
|
||||
* Encoded video output from a demuxer to parser / decoder or from encoders into a muxer.
|
||||
* Raw video buffers
|
||||
|
||||
The design below is somewhat based on the proposals from
|
||||
[bug 611157](https://bugzilla.gnome.org/show_bug.cgi?id=611157)
|
||||
|
||||
Multiview is used as a generic term to refer to handling both
|
||||
stereo content (left and right eye only) as well as extensions for videos
|
||||
containing multiple independent viewpoints.
|
||||
|
||||
Encoded Signalling
|
||||
------------------
|
||||
This is regarding the signalling in caps and buffers from demuxers to
|
||||
parsers (sometimes) or out from encoders.
|
||||
|
||||
For backward compatibility with existing codecs many transports of
|
||||
stereoscopic 3D content use normal 2D video with 2 views packed spatially
|
||||
in some way, and put extra new descriptions in the container/mux.
|
||||
|
||||
Info in the demuxer seems to apply to stereo encodings only. For all
|
||||
MVC methods I know, the multiview encoding is in the video bitstream itself
|
||||
and therefore already available to decoders. Only stereo systems have been retro-fitted
|
||||
into the demuxer.
|
||||
|
||||
Also, sometimes extension descriptions are in the codec (e.g. H.264 SEI FPA packets)
|
||||
and it would be useful to be able to put the info onto caps and buffers from the
|
||||
parser without decoding.
|
||||
|
||||
To handle both cases, we need to be able to output the required details on
|
||||
encoded video for decoders to apply onto the raw video buffers they decode.
|
||||
|
||||
*If there ever is a need to transport multiview info for encoded data the
|
||||
same system below for raw video or some variation should work*
|
||||
|
||||
### Encoded Video: Parameters to transmit in caps
|
||||
1. multiview-mode (called "Channel Layout" in bug 611157)
|
||||
* Whether a stream is mono, for a single eye, stereo, mixed-mono-stereo
|
||||
(switches between mono and stereo - mp4 can do this)
|
||||
* Uses a buffer flag to mark individual buffers as mono or "not mono"
|
||||
(single|stereo|multiview) for mixed scenarios. The alternative (not
|
||||
proposed) is for the demuxer to switch caps for each mono to not-mono
|
||||
change, and not used a 'mixed' caps variant at all.
|
||||
* _single_ refers to a stream of buffers that only contain 1 view.
|
||||
It is different from mono in that the stream is a marked left or right
|
||||
eye stream for later combining in a mixer or when displaying.
|
||||
* _multiple_ marks a stream with multiple independent views encoded.
|
||||
It is included in this list for completeness. As noted above, there's
|
||||
currently no scenario that requires marking encoded buffers as MVC.
|
||||
2. Frame-packing arrangements / view sequence orderings
|
||||
* Possible frame packings: side-by-side, side-by-side-quincunx,
|
||||
column-interleaved, row-interleaved, top-bottom, checker-board
|
||||
* bug 611157 - sreerenj added side-by-side-full and top-bottom-full but
|
||||
I think that's covered by suitably adjusting pixel-aspect-ratio. If
|
||||
not, they can be added later.
|
||||
* _top-bottom_, _side-by-side_, _column-interleaved_, _row-interleaved_ are as the names suggest.
|
||||
* _checker-board_, samples are left/right pixels in a chess grid +-+-+-/-+-+-+
|
||||
* _side-by-side-quincunx_. Side By Side packing, but quincunx sampling -
|
||||
1 pixel offset of each eye needs to be accounted when upscaling or displaying
|
||||
* there may be other packings (future expansion)
|
||||
* Possible view sequence orderings: frame-by-frame, frame-primary-secondary-tracks, sequential-row-interleaved
|
||||
* _frame-by-frame_, each buffer is left, then right view etc
|
||||
* _frame-primary-secondary-tracks_ - the file has 2 video tracks (primary and secondary), one is left eye, one is right.
|
||||
Demuxer info indicates which one is which.
|
||||
Handling this means marking each stream as all-left and all-right views, decoding separately, and combining automatically (inserting a mixer/combiner in playbin)
|
||||
-> *Leave this for future expansion*
|
||||
* _sequential-row-interleaved_ Mentioned by sreerenj in bug patches, I can't find a mention of such a thing. Maybe it's in MPEG-2
|
||||
-> *Leave this for future expansion / deletion*
|
||||
3. view encoding order
|
||||
* Describes how to decide which piece of each frame corresponds to left or right eye
|
||||
* Possible orderings left, right, left-then-right, right-then-left
|
||||
- Need to figure out how we find the correct frame in the demuxer to start decoding when seeking in frame-sequential streams
|
||||
- Need a buffer flag for marking the first buffer of a group.
|
||||
4. "Frame layout flags"
|
||||
* flags for view specific interpretation
|
||||
* horizontal-flip-left, horizontal-flip-right, vertical-flip-left, vertical-flip-right
|
||||
Indicates that one or more views has been encoded in a flipped orientation, usually due to camera with mirror or displays with mirrors.
|
||||
* This should be an actual flags field. Registered GLib flags types aren't generally well supported in our caps - the type might not be loaded/registered yet when parsing a caps string, so they can't be used in caps templates in the registry.
|
||||
* It might be better just to use a hex value / integer
|
||||
|
||||
Buffer representation for raw video
|
||||
-----------------------------------
|
||||
* Transported as normal video buffers with extra metadata
|
||||
* The caps define the overall buffer width/height, with GstVideoMeta to extract the individual views.
|
||||
* pixel-aspect-ratio adjusted if needed to double the overall width/height
|
||||
* video sinks that don't know about multiview extensions yet should show the '0th' GstVideoMeta and
|
||||
therefore the 'primary' view in a backwards compatible way for simple frame-packed transports.
|
||||
For frame-sequence outputs, things might look weird, but just adding multiview-mode to the sink caps
|
||||
can disallow those transports.
|
||||
* _row-interleaved_ packing is actually just side-by-side memory layout with half frame width, twice
|
||||
the height, so can be handled by adjusting the overall caps and strides
|
||||
* Other exotic layouts need new pixel formats defined (checker-board, column-interleaved, side-by-side-quincunx)
|
||||
* _Frame-by-frame_ - one view per buffer, but with alternating metas marking which buffer is which left/right/other view and using a new buffer flag as described above
|
||||
to mark the start of a group of corresponding frames.
|
||||
* New video caps addition as for encoded buffers
|
||||
|
||||
### Proposed Caps fields
|
||||
Combining the requirements above and collapsing the combinations into mnemonics:
|
||||
|
||||
* multiview-mode =
|
||||
mono | left | right | sbs | sbs-quin | col | row | topbot | checkers |
|
||||
frame-by-frame | mixed-sbs | mixed-sbs-quin | mixed-col | mixed-row |
|
||||
mixed-topbot | mixed-checkers | mixed-frame-by-frame | multiview-frames mixed-multiview-frames
|
||||
* multiview-flags =
|
||||
+ 0x0000 none
|
||||
+ 0x0001 right-view-first
|
||||
+ 0x0002 left-h-flipped
|
||||
+ 0x0004 left-v-flipped
|
||||
+ 0x0008 right-h-flipped
|
||||
+ 0x0010 right-v-flipped
|
||||
|
||||
### Proposed new buffer flags
|
||||
Add two new GST_VIDEO_BUFFER flags in video-frame.h and make it clear that those
|
||||
flags can apply to encoded video buffers too. wtay says that's currently the
|
||||
case anyway, but the documentation should say it.
|
||||
|
||||
**GST_VIDEO_BUFFER_FLAG_MULTIPLE_VIEW** - Marks a buffer as representing non-mono content, although it may be a single (left or right) eye view.
|
||||
**GST_VIDEO_BUFFER_FLAG_FIRST_IN_BUNDLE** - for frame-sequential methods of transport, mark the "first" of a left/right/other group of frames
|
||||
|
||||
### A new GstMultiviewMeta
|
||||
This provides a place to describe all provided views in a buffer / stream,
|
||||
and through Meta negotiation to inform decoders about which views to decode if
|
||||
not all are wanted.
|
||||
|
||||
* Logical labels/names and mapping to GstVideoMeta numbers
|
||||
* Standard view labels LEFT/RIGHT, and non-standard ones (strings)
|
||||
|
||||
Outputting stereo content
|
||||
-------------------------
|
||||
The initial implementation for output will be stereo content in glimagesink
|
||||
|
||||
### Output Considerations with OpenGL
|
||||
* If we have support for stereo GL buffer formats, we can output separate left/right eye images and let the hardware take care of display.
|
||||
* Otherwise, glimagesink needs to render one window with left/right in a suitable frame packing
|
||||
and that will only show correctly in fullscreen on a device set for the right 3D packing -> requires app intervention to set the video mode.
|
||||
* Which could be done manually on the TV, or with HDMI 1.4 by setting the right video mode for the screen to inform the TV or third option, we
|
||||
support rendering to two separate overlay areas on the screen - one for left eye, one for right which can be supported using the 'splitter' element and 2 output sinks or, better, add a 2nd window overlay for split stereo output
|
||||
* Intel hardware doesn't do stereo GL buffers - only nvidia and AMD, so initial implementation won't include that
|
||||
|
||||
## Other elements for handling multiview content
|
||||
* videooverlay interface extensions
|
||||
* Element message to communicate the presence of stereoscopic information to the app
|
||||
* New API for the app to set rendering options for stereo/multiview content
|
||||
* This might be best implemented as a **multiview-disposition GstContext**, so that
|
||||
the pipeline can share app preferences for (in particular) downmixing
|
||||
to mono for output, or in the sink
|
||||
* Converter element
|
||||
* convert different view layouts
|
||||
* Render to anaglyphs of different types (magenta/green, red/blue, etc) and output as mono
|
||||
* Mixer element
|
||||
* take 2 video streams and output as stereo
|
||||
* later take n video streams
|
||||
* share code with the converter, it just takes input from n pads instead of one.
|
||||
* Splitter element
|
||||
* Output one pad per view
|
||||
|
||||
### Implementing MVC handling in decoders / parsers (and encoders)
|
||||
Things to do to implement MVC handling
|
||||
|
||||
1. Parsing SEI in h264parse and setting caps (patches available in
|
||||
bugzilla for parsing, see below)
|
||||
2. Integrate gstreamer-vaapi MVC support with this proposal
|
||||
3. Help with [libav MVC implementation](https://wiki.libav.org/Blueprint/MVC)
|
||||
4. generating SEI in H.264 encoder
|
||||
5. Support for MPEG2 MVC extensions
|
||||
|
||||
### Relevant bugs
|
||||
[bug 685215](https://bugzilla.gnome.org/show_bug.cgi?id=685215) - codecparser h264: Add initial MVC parser
|
||||
[bug 696135](https://bugzilla.gnome.org/show_bug.cgi?id=696135) - h264parse: Add mvc stream parsing support
|
||||
[bug 732267](https://bugzilla.gnome.org/show_bug.cgi?id=732267) - h264parse: extract base stream from MVC or SVC encoded streams
|
||||
|
||||
Loading…
Reference in a new issue