Use unbuffered async mode by default, and when in unbuffered mode,
decouple audio/video so that audio plays as soon as it's received.
This is a workaround for decklink device drivers having unreliable
video/audio timestamps (audio/video sync drifting over time). From
testing, it seems that the handling of video and audio is completely
separate in the driver; along with the timestamp calculations. For
example, when the thread of the decklink audio callback is stalled, it
would cause the timestamps of the audio alone to go out of sync, which
indicates timestamps are calculated more or less on the spot independent
of what video is doing (which is how we replicated the issue fixed by
b63e4b055e68a). Because decklink drivers treats the audio and video as
essentially decoupled, we must also treat it as decoupled. This is what
was causing video/audio to drift out of sync over time.
This replaces the name-based detection of the 4K intensity pro, and
allows other devices to be able to use the BGRA pixel format, if the
user so chooses.
cleaning up my previous commit a bit. we can just keep the
appropriate BMDPixelFormat as a data member and keep StartCapture() a
bit clearer.
this might also be helpful if (when?) the detection code needs to be
more robust or configurable
detect the device type when initializing the device instance and
determine whether to capture YUV or RGB. tested with a Blackmagic
Intensity Pro and a Blackmagic Intensity Pro 4K in the same machine,
capturing at the same time, on Linux
This is my fault; I made an idiotic assumption about the data and it
ended up causing the plugin to crash. This is definitely one of my more
embarrassing moments.
System timestamps were being used instead of timestamps from the
audio/video input. This would cause potential desync as well as
incremental buffering when using devices with the blackmagic video
source. Using the timestamps direct from the SDK itself fixes those
issues, and causes audio/video to play back properly and in sync.
