The workers run in separate threads meaning if any significant change is made
(e.g. parameters changing, or even closing the program), these workers may still
be mid-render. This is particularly problematic when closing since the nodes a
worker is rendering may be deleted mid-render. Render backends now have a
function that pauses the main thread (but starts a second event loop so the UI
isn't frozen) until the worker threads are all finished. This way, massive
changes can be made safely without race conditions.
We try to handle aspect ratios in metadata (e.g. stretching 1440x1080 videos
out to 1920x1080 when requested), and FFmpeg will usually return a 1/1
aspect ratio even if it can't determine an aspect ratio. However, as mentioned
in the documentation, sometimes it returns a 0/0 aspect ratio when it can't
determine an aspect ratio, which we didn't handle and would lead to the code
allocating a buffer with a 0px height. This commit handles both 1/1 and 0/0
aspect ratios in accordance with the FFmpeg documentation.
Reference: https://www.ffmpeg.org/doxygen/4.0/structAVFrame.html#a62f9c20541a83d37db7072126ff0060d
`rational` is supposed to "fix signs" and "reduce" whenever its values are set,
but I neglected to do this when its values were set by an AVRational. Now it
will do so on both.
Implementation isn't perfect yet, viewer/renderer doesn't update yet when
the preference is changed so a sequence needs to be re-opened for the change to
take effect.
By using one thread per logical CPU thread, we seemed to completely saturate
the CPU which would kill the performance of the main/GUI thread (despite the
other threads being low priority). We now use half of the logical threads, which
still sees good CPU usage and minimal performance impact while allowing the
main thread to respond to user actions.
itsmattkc