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Old 18 Jul 2003, 07:48 AM   #1
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Default Does max keyframe interval affect video quality?

Can anyone answer the following...?


Does using a lower max keyframe interval actually produce a better quality video? or does it just facilitate cutting the video?

Is it possible to set it too low?

thanks!
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Old 18 Jul 2003, 08:39 AM   #2
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"Is it possible to set it too low?"

Yes. You might get to the point where your system cannot keep up with the requirements of outputting too many keyframes (full image frames) in rapid sequence...
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Old 18 Jul 2003, 09:06 AM   #3
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Default Re: Does max keyframe interval affect video quality?

Quote:
Originally posted by otwist26
Can anyone answer the following...?


Does using a lower max keyframe interval actually produce a better quality video? or does it just facilitate cutting the video?

Is it possible to set it too low?

thanks!
The more keyframes inserted, the larger the fle size. When your media player is seeking it must seek to a keyframe to play. So lets say you have one KF at frame 0 and seek to say 5 min into clip, your player must decode ALL frames from 0 which may take a long time.

Most codecs, if setup right, will insert a keyframe at every scene change which normally suffices.

I normally set max KF to say 250 which would be 10sec for PAL (25fps) or 300 for NTSC (30fps approx)

The more keyframes inserted will help you when it come to cutting alright. Remeber, the cut needs only BEGIN with a keyframe, not end. Good luck.

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Old 18 Jul 2003, 09:45 AM   #4
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Edge,

I understand that part about keyframes. I guess what I'm wondering is.... Is a keyframe a better quality frame than a delta frame (fewer artifacts, better picture, etc.)?
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Old 18 Jul 2003, 09:47 AM   #5
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Quote:
Originally posted by setarip
Yes. You might get to the point where your system cannot keep up with the requirements of outputting too many keyframes (full image frames) in rapid sequence...
Setarip,

This would be a problem when playing back the movie, not in actually generating it, correct?
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Old 18 Jul 2003, 10:05 AM   #6
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Quote:
Originally posted by otwist26
Edge,

I understand that part about keyframes. I guess what I'm wondering is.... Is a keyframe a better quality frame than a delta frame (fewer artifacts, better picture, etc.)?
Yes, as it does not need any other frames as reference.

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Old 18 Jul 2003, 12:24 PM   #7
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"Setarip,

This would be a problem when playing back the movie, not in actually generating it, correct?"

Yes, if it were to be a problem, it would only be regarding playback (That's what I was referred to as "outputting")...
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