[libcamera-devel] [PATCH 0/3] Sequence Observer

[Kieran Bingham]

Quoting Laurent Pinchart (2022-05-09 14:33:00)
> Hi Kieran,
> 
> On Fri, Apr 29, 2022 at 09:34:31PM +0200, Kieran Bingham via libcamera-devel wrote:
> > This fell out of some more work I did in the past catching and detecting
> > frame drops in streams. While the method of reporting this event to
> > userspace is debated, this pulls out some core functionality and wraps
> > some generic code into a Sequence Observer to provide an easy to use
> > check on any monotonic sequence.
> > 
> > For now - it simply reports a warning if a V4L2 device detects a frame
> > drop, which is more notification that we have currently... as we are
> > silently dropping frames at the moment.
> 
> Even if we haven't finalized the way to handle frame drops in the
> application-facing API, I think it's useful to be able to be notified of
> frame drops already. I'm however thinking that the sequence observer
> class is a bit overkill at this point. I'd recommend starting with an
> ad-hoc solution in V4L2VideoDevice only, and later extend it if
> required.

Of course this did start of as an ad-hoc solution in V4L2VideoDevice and
then became the observer because I had the same snippets of
functionality in 4 different places. (But I think you don't like those
either so ... we'll find out later).

But anyway, that's why I split this out as I thought it was a helpful
... helper.

As it happens, I need to put more thought and consideration into this
anyway, as a warning print really is too noisy anyway - so I don't think
it can even suffice as a starting point to print a warning (Perhaps a
Debug though)

(I am partialy concerned that we can have so many frame drops that a
warning print can be too noisy, but I think that it probably would be
expected behaviour in some scenarios, even if we weren't using
libcamera).

> 
> > Kieran Bingham (3):
> >   libcamera: Add sequence value observer
> >   test: Add Sequence observer tests
> >   libcamera: v4l2: Detect frame drops on V4L2VideoDevice
> > 
> >  include/libcamera/internal/v4l2_videodevice.h |  2 +
> >  include/libcamera/meson.build                 |  1 +
> >  include/libcamera/sequence.h                  | 20 +++++
> >  src/libcamera/meson.build                     |  1 +
> >  src/libcamera/sequence.cpp                    | 66 +++++++++++++++
> >  src/libcamera/v4l2_videodevice.cpp            | 10 +++
> >  test/meson.build                              |  1 +
> >  test/sequence.cpp                             | 80 +++++++++++++++++++
> >  8 files changed, 181 insertions(+)
> >  create mode 100644 include/libcamera/sequence.h
> >  create mode 100644 src/libcamera/sequence.cpp
> >  create mode 100644 test/sequence.cpp
> 
> -- 
> Regards,
> 
> Laurent Pinchart