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Jerky video playback

video playback

Problem:

 

Since the 4.0.3 version, video playback in Analyzer and InTheAction modules is sometimes jerky.

 

Answer:

 

In 4.0.3 release was implemented a new function called ASR (Adaptive Sampling Rate).

The purpose of this function is to ensure the speed accuracy of a video replay by altering the quality of the playback in the case your computer cannot keep up with the speed at full quality.

In other terms, it will handicap quality in order to play the clip at the correct speed all the time.

 

You can see the current state of the ASR by looking at the two green dots in the video status bar:

 

 

Note: 1 frame consists of 2 fields. Dartfish Software letting you see all fields, it means you have theorically doubled frames-per-second.

  • Both dots ON: All fields are displayed (50 frames-per-second PAL/60 fps NTSC)
  • One dot ON: Half of the fields are displayed (25 fps PAL/30 fps NTSC)
  • Both dots OFF: Quarter of the fields are displayed (12 fps PAL/15 fps NTSC)

 

Now, here is an explanation for this jerkiness feeling in the playback:

 

Computers often feature what is called a "Throttle mode". This mode is designed to save energy. What it does, is that it reduces the processor's (CPU) clock speed in real time, depending on the processor's charge.

Problem is, Throttle mode and our ASR doesn't work correctly in conjunction. When ASR is full, it often still doesn't load the CPU to the max. Therefore, throttle mode is engaged, and reduces the CPU speed. Then, ASR detects the CPU charge as higher, and therefore drops to one dot mode. Again, throttle detects the CPU as not overloaded and reduces speed again. And finally ASR drops to no dots mode, which can give the jerkiness feeling in the playback.

To solve this issue, you have to force your laptop not to use it's throttle function:

  1. Click Windows' "Start" menu
  2. Select "Control Panel"
  3. Select "Power Options"
  4. Click "Power Schemes" tab
  5. In the dropdown box, select "Always ON"

This should ensure the throttle mode stays off.

Then ASR shouldn't be a problem anymore. But, if you still have unsatisfying playback, you can try and disable the ASR function and see if it's better:

  1. Inside Dartfish, select the "Tools" menu
  2. Click "Options"
  3. Select the "Advanced" entry in the left-hand menu
  4. Untick "Enable Automatic Sampling Rate for Analyzer and InTheAction" option, and press ok to close the options panel

The replay will maybe look smoother, but keep in mind that the replay speed will not be guaranteed anymore.

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