The presentation time in fMP4 is calculated by adding and subtracting
3 values. All 3 values are currently converted to microseconds first
before the calculation, leading to rounding errors. The rounding errors
can be avoided by doing the conversion to microseconds as the last step.
For example:
In timescale 96000: 8008+8008-16016 = 0
Rounding to us first: 83416+83416-166833=-1
#minor-release
PiperOrigin-RevId: 406809844
Test file produced with:
$ MP4Box -add "sample.mp4#video:colr=nclc,1,1,1" -new sample_18byte_nclx_colr.mp4
And then manually changing the `nclc` bytes to `nclx`.
This produces an 18-byte `colr` box with type `nclx`. The bitstream of
this file does not contain HDR content, so the file itself is invalid
for playback with a real decoder, but adding the box is enough to test
the extractor change in this commit.
(aside: MP4Box will let you pass `nclx`, but it requires 4 parameters, i.e. it
requires the full_range_flag to be set, resulting in a valid 19-byte colr box)
#minor-release
Issue: #9332
PiperOrigin-RevId: 405842520
