Many improvements for smooth audio playback when 'time' keyframes are used for time remapping.

- Added new Frame::ReverseAudio() helper method - for time keyframe support playing backwards audio
- Fixed math rounding error on time keyframe Resampler, to use the rounded source samples value
- Removed some unused args and Frame audio methods
- Reset FrameMapper resample context when non-adjacent frames are requested
- Correctly reverse Frame audio if a time keyframe is present, and reversing audio
- Rewrite Keyframe::IsIncreasing() function, to give accurate direction of time keyframes at any index (special logic to support first and last indexes)
- Fixed Keyframe unit tests - since logic has changed a bit
- Improved time mapping unit tests
- Replace many c-style casts with static_cast
- Added new sine.wav test file

src/FFmpegWriter.cpp

@@ -1628,7 +1628,7 @@ void FFmpegWriter::write_audio_packets(bool is_final) {
 		// Get audio sample array
 		float *frame_samples_float = NULL;
 		// Get samples interleaved together (c1 c2 c1 c2 c1 c2)
-		frame_samples_float = frame->GetInterleavedAudioSamples(sample_rate_in_frame, NULL, &samples_in_frame);
+		frame_samples_float = frame->GetInterleavedAudioSamples(&samples_in_frame);
 
 		// Calculate total samples
 		total_frame_samples = samples_in_frame * channels_in_frame;