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I have a DSLR camera which can record a HD movie at 60fps. My question is that, sometimes when recording, the FPS seems to drop below 60fps. What caused this problem? I used a class 10/UHS-1 SD card with transfer rate up to 45MB/s.

  • An uneducated guess: variable bitrate encoding. – jiggunjer Dec 15 '15 at 3:54
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Are you sure it's dropping frames? I have a canon 5d and it never drops frames, it simply stops recording when it can't keep up.

My guess is the file is fine, but the preview on the LCD is dropping frames.

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  • I mean that when I play the video, it seems a bit laggy during specific period. I did the preview on my laptop as well and it showed the same thing. My laptop should be powerful enough to play the video. – rcs Dec 16 '15 at 1:35
  • That should be easy to confirm, even a fast computer can drop frames occasionally. If you go frame by frame then there should be duplicate frames where the skipping occurs. – screaming drills Dec 16 '15 at 1:37
  • I see.. Let me check the video file again later and verify. – rcs Dec 16 '15 at 1:46
  • try exporting the video to another file format from your favourite player or editor. If the video lags at the same place then the corruption is baked in and not a playback issue (as the software doesn't care about maintaining audio sync during export). – 3pointedit Jan 29 '16 at 11:22
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You must remember that the bitrate of the compressed file does not represent the decompressed file size. Your PC is trying to reconstruct 60 full HD frames per second without a specific chip set to do it (whereas your camera is designed for this one task).

It is not at all surprising that it cannot achieve this, especially if there is not enough video ram allocated to displaying all the data. Many Video Editing applications will scale the dimensions or frame rate to retain audio sync playback. Consider creating a higher bitrate file that requires less processing time per frame but uses more memory to decompress. This should alleviate some of the stress on the CPU for decompressing.

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  • This issue is that the camera doesn't maintain recording at 60fps, not playback afterwards. – Gyan Jan 28 '16 at 15:54
  • How did you determine that the fault is with the recording? My experience of Canon cameras dropping frames is that they tend to hold a frame instead of loose sync, so that you get a stuttering playback. – 3pointedit Jan 29 '16 at 11:10
  • The question is about recording - doesn't mention anything about playback. In any case, modern PCs can easily decode 60fps baseline profile H.264 like a camera would record. – Gyan Jan 29 '16 at 11:15

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