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Fix FrameAtTime computation for CFR

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The new formula is just the inverse function of the CFR part of
the TimeAtFrame function.

To see how the previous implementation was faulty, see either the added
tests, or
- In Aegisub, open a dummy video with a frame rate of 23.976
- Make a subtitle event with start time 04:44.41
- Double-click the line to (supposedly) seek to its first frame
- This will seek one frame earlier than it should, and the event will
  not be displayed on the resulting frame.
This commit is contained in:
arch1t3cht 2022-11-01 11:26:57 +01:00
parent a394aefd1a
commit 245cc68afa
2 changed files with 19 additions and 1 deletions
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2
libaegisub/common/vfr.cpp
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@ -225,7 +225,7 @@ int Framerate::FrameAtTime(int ms, Time type) const {
return int((ms * numerator / denominator - 999) / 1000);
if (ms > timecodes.back())
return int((ms * numerator - last + denominator - 1) / denominator / 1000) + (int)timecodes.size() - 1;
return int((ms * numerator - numerator / 2 - last + numerator - 1) / denominator / 1000) + (int)timecodes.size() - 1;
return (int)distance(lower_bound(timecodes.rbegin(), timecodes.rend(), ms, std::greater<int>()), timecodes.rend()) - 1;
}

18
tests/tests/vfr.cpp
View file

@ -149,6 +149,12 @@ TEST(lagi_vfr, cfr_round_trip_exact) {
for (int i = -10; i < 11; i++) {
EXPECT_EQ(i, fps.FrameAtTime(fps.TimeAtFrame(i)));
}
ASSERT_NO_THROW(fps = Framerate(24000, 1001));
int frames[] = {-100, -10, -1, 0, 1, 10, 100, 6820};
for (int i : frames) {
EXPECT_EQ(i, fps.FrameAtTime(fps.TimeAtFrame(i)));
}
}
TEST(lagi_vfr, cfr_round_trip_start) {
@ -157,6 +163,12 @@ TEST(lagi_vfr, cfr_round_trip_start) {
for (int i = -10; i < 11; i++) {
EXPECT_EQ(i, fps.FrameAtTime(fps.TimeAtFrame(i, START), START));
}
ASSERT_NO_THROW(fps = Framerate(24000, 1001));
int frames[] = {-100, -10, -1, 0, 1, 10, 100, 6820};
for (int i : frames) {
EXPECT_EQ(i, fps.FrameAtTime(fps.TimeAtFrame(i, START), START));
}
}
TEST(lagi_vfr, cfr_round_trip_end) {
@ -165,6 +177,12 @@ TEST(lagi_vfr, cfr_round_trip_end) {
for (int i = -10; i < 11; i++) {
EXPECT_EQ(i, fps.FrameAtTime(fps.TimeAtFrame(i, END), END));
}
ASSERT_NO_THROW(fps = Framerate(24000, 1001));
int frames[] = {-100, -10, -1, 0, 1, 10, 100, 6820};
for (int i : frames) {
EXPECT_EQ(i, fps.FrameAtTime(fps.TimeAtFrame(i, END), END));
}
}
TEST(lagi_vfr, vfr_round_trip_exact) {