GothPlayer is a basic video player for TV, DVD and video files with focus on one specific feature, namely frame lock. Frame lock means that the refresh rate of the computer display (number of times per second a new image is shown on the computer display) and the frame rate of the video to be shown (number of unique images per second in the video) are fully synchronized. This eliminates pan judder, i.e. skipped or duplicated video frames, most visible when watching long pan shots.

Pan judder is usually not a problem with regular TVs, DVD players etc since they generate a video signal for the display that is in sync with the produced video signal (it would actually be harder to produce a signal to the display that was out of sync with the video in such devices). Regular PCs lack this synchronization because the PC was not originally designed to show video. The graphics board typically produces a video signal to the display totally ignorant of what type of information it receives from the CPU and when it receives it. When the graphics board decides it’s time to display a new frame, it just displays what it finds in the particular part of its memory called the front buffer.

Clearly visible pan judder can be observed when watching a 25 frames per second (fps) PAL DVD or a 24 fps Blue-ray movie on a regular laptop computer that typically has a 60 Hz display refresh rate. The challenge in this set-up is that the 24/25 fps produced by the player need to be portioned out on the 60 “slots” a second that the laptop display has to show a new image (to refresh). To fit, some of the video frames will be shown twice and some will be shown three times producing uneven (jerky, stuttering) video. If the difference in the video frame rate and the display refresh rate is smaller, the jerkiness will be less frequent, but as long as there is a difference, then sooner or later a frame needs to be shown twice or skipped resulting in a motion artifact. For a good discussion on frame rate matching, follow this link. (The article describes a method to avoid a consequence of poor synchronization, a kind of jitter that arises when a new frame arrives to the renderer just around the vertical sync. In those cases the frame and a few consecutive frames may randomly end up before and after their respective vsync causing severe stutter.)

GothPlayer has two options for synchronization:

  • Synchronization of the refresh rate of the computer display to the frame rate of the incoming video. This mode works with live video sources such as TV, the frame rate of which can not be controlled by the PC of obvious reasons. This is the “cleanest” form of synchronization but works only with some graphics boards, displays and display resolutions.
  • Synchronization of the frame rate of the incoming video to the refresh rate of the display (the opposite of above). This works with any display capable of a refresh rate that is (close to) an even multiple of the video frame rate (i.e. 48 Hz refresh rate for 24 fps movies) but does of natural reasons not work for live sources.

GothPlayer can optionally be set to use exclusive mode fullscreen video which seems to give more exact timing characteristics. In exclusive mode, Direct3D communicates directly with the display driver avoiding GDI (Graphics Device Interface, a Windows component that is responsible for representing graphical objects and transmitting them to output devices such as monitors), which is probably the reason for the more exact timing. Exclusive mode also seems less prone to tearing.

Windowed mode fullscreen can also be used and works fine with newer graphics boards and powerful computers as long as the video and the display are kept in sync with any of the two sync mechanisms described above. When they get out of sync, the resulting judder can be aggravated by tearing.

You are very welcome to download the player (see the Get started page) and try it out but please note that it is an experimental software application and there are no guarantees or claims whatsoever, implicit or explicit, that it will error-free. I would appreciate any feedback you may have regarding the player.

Screenshot
A screenshot of the GothPlayer in windowed mode. The on-screen info is only used for performance monitoring and can of course be turned off.

This page has the following sub pages.