This reworks all of mpv's unit tests so they are compiled as separate
executables (optional) and run via meson test. Because most of the tests
are dependant on mpv's internals, existing compiled objects are
leveraged to create static libs and used when necessary. As an aside, a
function was moved into video/out/gpu/utils for sanity's sake (otherwise
most of vo would have been needed). As a plus, meson multithreads
running tests automatically and also the output no longer pollutes the
source directory. There are tests that can break due to ffmpeg changes,
so they require a specific minimum libavutil version to be built.
Maybe this is useful for some of the lesser VOs. It's preferable over
bad ad-hoc solutions based on the more complex sub_bitmap data
structures (as observed e.g. in vo_vaapi.c), and does not use that much
more code since draw_bmp already created such an overlay internally.
But I still wanted something that avoids having to upload/render a full
screen-sized overlay if for example there's only a tiny subtitle line on
the bottom of the screen. So the new API can return a list of modified
pixels (for upload) and non-transparent pixels (for display). The way
these pixel rectangles are computed is a bit dumb and returns dumb
results, but it should be usable, and the implementation can change.
draw_bmp.c is the software blender for subtitles and OSD. It's used by
encoding mode (burning subtitles), and some VOs, like vo_drm, vo_x11,
vo_xv, and possibly more.
This changes the algorithm from upsampling the video to 4:4:4 and then
blending to downsampling the OSD and then blending directly to video.
This has far-reaching consequences for its internals, and results in an
effective rewrite.
Since I wanted to avoid un-premultiplying, all blending is done with
premultiplied alpha. That's actually the sane thing to do. The old code
just didn't do it, because it's very weird in YUV fixed point.
Essentially, you'd have to compensate for the chroma centering constant
by subtracting src_alpha/255*128. This seemed so hairy (especially with
correct rounding and high bit depths involved) that I went for using
float.
I think it turned out mostly OK, although it's more complex and less
maintainable than before. reinit() is certainly a bit too long. While it
should be possible to optimize the RGB path more (for example by
blending directly instead of doing the stupid float conversion), this is
probably slower. vo_xv users probably lose in this, because it takes the
slowest path (due to subsampling requirements and using YUV).
Why this rewrite? Nobody knows. I simply forgot the reason. But you'll
have it anyway. Whether or not this would have required a full rewrite,
at least it supports target alpha now (you can for example hard sub
transparent PNGs, if you ever wanted to use mpv for this).
Remove the check in vf_sub. The new draw_bmp.c is not as reliant on
libswscale anymore (mostly uses repack.c now), and osd.c shows an
error message on missing support instead now.
Formats with chroma subsampling of 4 are not supported, because FFmpeg
doesn't provide pixfmt definitions for alpha variants. We could provide
those ourselves (relatively trivial), but why bother.
Making OSD/subtitle bitmaps refcounted was planend a longer time ago,
e.g. the sub_bitmaps.packed field (which refcounts the subtitle bitmap
data) was added in 2016. But nothing benefited much from it, because
struct sub_bitmaps was usually stack allocated, and there was this weird
callback stuff through osd_draw().
Make it possible to get actually refcounted subtitle bitmaps on the OSD
API level. For this, we just copy all subtitle data other than the
bitmaps with sub_bitmaps_copy(). At first, I had planned some fancy
refcount shit, but when that was a big mess and hard to debug and just
boiled to emulating malloc(), I made it a full allocation+copy. This
affects mostly the parts array. With crazy ASS subtitles, this parts
array can get pretty big (thousands of elements or more), in which case
the extra alloc/copy could become performance relevant. But then again
this is just pure bullshit, and I see no need to care. In practice, this
extra work most likely gets drowned out by libass murdering a single
core (while mpv is waiting for it) anyway. So fuck it.
I just wanted this so draw_bmp.c requires only a single call to render
everything. VOs also can benefit from this, because the weird callback
shit isn't necessary anymore (simpler code), but I haven't done anything
about it yet. In general I'd hope this will work towards simplifying the
OSD layer, which is prerequisite for making actual further improvements.
I haven't tested some cases such as the "overlay-add" command. Maybe it
crashes now? Who knows, who cares.
In addition, it might be worthwhile to reduce the code duplication
between all the things that output subtitle bitmaps (with repacking,
image allocation, etc.), but that's orthogonal.
In order to support OSD redrawing for vo_xv and vo_x11, draw_bmp.c
included an awkward "backup" mechanism to copy and restore image
regions that have been changed by OSD/subtitles.
Replace this by a much simpler mechanism: keep a reference to the
original image, and use that to restore the Xv/X framebuffers.
In the worst case, this may increase cache pressure and memory usage,
even if no OSD or subtitles are rendered. In practice, it seems to be
always faster.
In order to improve performance, vo_xv didn't create a backup of the
video frame before drawing OSD and subtitles during normal playback. It
required the frontend to do frame stepping if it wanted to redraw the
OSD, but no backup of the video frame was available. (Consider the
following use case: enable the OSD permanently with --osd-level=3, then
pause during playback and do something that shows an OSD message. The
player will advance the video by one frame at the time the new OSD
message is first drawn.)
This also meant that taking a screenshot during playback with vo_xv
would include OSD and subtitles in the resulting image.
Fix this by always creating a backup before drawing OSD or subtitles.
In order to avoid having to create a full copy of the whole image frame,
introduce a complex scheme that tries to backup only the changed
regions.
It's unclear whether the additional complexity in draw_bmp.c for
backing up only the changed areas of the frame is worth it. Possibly
a simpler implementation would suffice, such as tracking only Y ranges
of changed image data, or even just copying the full frame.
vo_xv's get_screenshot() now always creates a copy in order not to
modify the currently displayed frame.
Dudemanguy
wm4
Rudolf Polzer