Improve seeking
Reduce seek times while dragging.
Make drag to the beginning correct.
No block while dragging progress bar.
No need to get url every time.
Prevent deadlock while dragging backwards.
Try 3 times.
Same time format for both sides
Improve seek small offset.
Prevent set window ratio in full screen
Improve audio syncing by make video buffer larger.
Clear dead code
Add download pdf file directly.
Fix syncing problem
Wrong end file condition
Improve buffering
Wrong spelling
Remove some prints
Use slice instead of list
Fix bug: display wrong speed in progress bar.