- Use a divider of 1 (full resolution) for new sequences and for
footage-derived viewer parameters instead of the auto-downscaling
heuristic, so the viewer defaults to full-res preview.
- In AudioWaveformView, base the view timebase on the video frame rate
when video is present; fall back to the audio sample rate only for
audio-only sources. Using the audio sample rate as the view timebase
created an enormous scene rect (time * sample_rate * scale), which
froze the waveform view and stalled playback updates when showing
the audio waveform.