VideoClock

Overview

Using VideoClock, you can achieve ultra smooth video playback. VideoClock makes minor adjustments to clock frequencies so that video is played in perfect sync with your display's refresh rate.

You can enable VideoClock in Options > Video. VideoClock. Like other audio features, it is not available when bitstreaming audio.

It is advisable to have Display Settings set up to automatically change the display's refresh rate. See Video Playback Options > Display Settings.

Technical Description

When playing a video, many factors combine to produce the synchronized audio and video. To maintain the lip-sync between audio and video, there is a "clock" that is in control of playback.

Normally this clock runs at normal speed (1.0x). If audio or video drift apart because the monitor or soundcard have a slightly different rates, a clock correction is issued. These clock corrections are called clock jitter, and they will cause the video to pause a little or drop frames.

VideoClock changes this approach. It makes minor changes to clock rates to perfectly match the rate of creation of frames to the rate of consumption by the display so that frames are never dropped or paused. A variation between source frames per second (fps) and display refresh rate of up to 5% can be dealt with.

Now, when lip-sync is slightly out of step, the audio is slowed or hastened. Normally this change is a tiny fraction of a percent and so not perceptible.

Target Ratio including PAL Speeddown

VideoClock adjusts the clock rate slightly to achieve an "ideal" ratio between the display refresh rate and video frame rate. This ensures, for example, that playing a 23.97 fps movie on a 24.0 Hz display will have a perfect 1:1 relationship. This is done by altering the clock by the tiny fraction 23.97/24.00. This removes the annoying occasional video stutter that would happen without this adjustment. The tiny audio change is inaudible.

This feature is also useful for PAL content that was originally shot at 23.97 fps and is recorded on disc or media at 25 fps. If played back at on a display set to 25 or 50 Hz, the movie would be slightly shorter and the audio pitch would be slightly higher. When playing these 25 fps files with the display rate set at 24 Hz, the movie will be played at the correct rate and the audio at the correct pitch. This requires the fps setting for these files to be changed to 23.97 fps.

VideoClock is willing to adjust the clock by up to 5% if it will result in a perfect ratio between the video and monitor rates.

Compared with ReClock

VideoClock has several key advantages compared with ReClock:

• Integrated with the JRiver audio engine, so all other features (JRSS, Room Correction, internal volume, Convolver etc.) are available
• Works with all output modes (ASIO, WASAPI, etc.)
• Talks directly to madVR to determine the monitor refresh rate so the target ratio is perfect when using madVR