On Tue, Aug 24, 2021 at 07:00:54PM -0700, Dan Dennedy wrote: > On Tue, Aug 24, 2021 at 6:06 PM amindfv--- via Mlt-devel < > mlt-devel@lists.sourceforge.net> wrote: > > > Thank you, this is exactly the type of clear answer I was hoping for! > > > > A couple follow-up questions: > > > > - I seem to be able to, with the calculation on line 371 linked below, > > get frame-inaccurate results, i.e. dropped or added frames. For example, > > with the simple timecode "01:01:00.1" at 23.976 fps: I think the un-rounded > > value should be 87754.5576, so I'd expect the rounded value to be either > > 87754 or 87755. However, it's 87753! [0] I think this may be caused by > > using "floor" for the hours and minutes, in combination with the fractional > > frame rate. > > > > > 23.976 is the rounded form of 24000/1001, which is the more typical value. > In any case, from here you can see unit tests that exercise this: > > https://github.com/mltframework/mlt/blob/master/src/tests/test_properties/test_properties.cpp#L188 > > A few of these cycle through 9999999 frames (over 11 hours at 240 fps) at > some common frame rates to ensure that when you convert from frame number > to a clock time value and back that you get the same frame number. But I do > not think every frame rate is going to work with the limited precision of > milliseconds.
Awesome! > > > > - It seems `lrint` determines its rounding direction depending on values > > in the current environment. That seems to mean a user can also lose sample > > accuracy if, for example, `lrint` rounds one way on my machine and then a > > friend reads my .mlt file with a different rounding direction. Is this true? > > > > > Not to my understanding. The rounding mode can be set programmatically > using fesetround() where the "e" refers to an "environment" in the > documentation, but that is not the same thing as an environment variable. > It refers to the process runtime state and mentions no environment > variables. MLT does not call this, and while it is possible an application > has that seems rather rare. I'd still wonder about differences in defaults across platforms but this is good enough for me, thanks. Tom _______________________________________________ Mlt-devel mailing list Mlt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mlt-devel
