On Thu September 13 2012 22:50:32 Laurent Pinchart wrote: > Hi Sakari, > > On Thursday 13 September 2012 23:38:14 Sakari Ailus wrote: > > On Fri, Sep 07, 2012 at 03:29:12PM +0200, Hans Verkuil wrote: > > > From: Hans Verkuil <hans.verkuil@xxxxxxxxx> > > > > > > Add a new flag that tells userspace that the monotonic clock is used > > > for timestamps and update the documentation accordingly. > > > > > > We decided on this new flag during the 2012 Media Workshop. > > > > > > Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx> > > > --- > > > > > > Documentation/DocBook/media/v4l/io.xml | 10 +++++++--- > > > Documentation/DocBook/media/v4l/vidioc-dqevent.xml | 3 ++- > > > Documentation/DocBook/media/v4l/vidioc-querycap.xml | 7 +++++++ > > > include/linux/videodev2.h | 1 + > > > 4 files changed, 17 insertions(+), 4 deletions(-) > > > > > > diff --git a/Documentation/DocBook/media/v4l/io.xml > > > b/Documentation/DocBook/media/v4l/io.xml index 2dc39d8..b680d66 100644 > > > --- a/Documentation/DocBook/media/v4l/io.xml > > > +++ b/Documentation/DocBook/media/v4l/io.xml > > > @@ -582,10 +582,14 @@ applications when an output stream.</entry> > > > > > > <entry>struct timeval</entry> > > > <entry><structfield>timestamp</structfield></entry> > > > <entry></entry> > > > > > > - <entry><para>For input streams this is the > > > + <entry><para>This is either the > > > > > > system time (as returned by the <function>gettimeofday()</function> > > > > > > -function) when the first data byte was captured. For output streams > > > -the data will not be displayed before this time, secondary to the > > > +function) or a monotonic timestamp (as returned by the > > > +<function>clock_gettime(CLOCK_MONOTONIC, &ts)</function> function). > > > +A monotonic timestamp is used if the > > > <constant>V4L2_CAP_MONOTONIC_TS</constant> +capability is set, otherwise > > > the system time is used. > > > +For input streams this is the timestamp when the first data byte was > > > captured. +For output streams the data will not be displayed before this > > > time, secondary to the > > I have an alternative proposal. > > > > The type of the desired timestamps depend on the use case, not the driver > > used to capture the buffers. Thus we could also give the choice to the user > > by means of e.g. a control. > > Or a buffer flag. I will need something similar to select device-specific > timestamps. > > However, for wall clock vs. monotonic clock, I don't think there's a reason to > let applications decide to use the wall clock. It would be a broken use case. > I don't think we should let applications decide in this case. I agree. > On the other hand, reporting a timespec instead of a timeval would be a good > idea. I'm tempted. Microsecond precision seems more than sufficient to me for video frames. I see no good reason for messing around with the v4l2_buffer struct just to get a timespec in. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
