Force frame rate of FFMpegFileWriter input #5453
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The output video file was observed to skip frames, when input frame rate does not match output (e.g., when fps=1, or interval=1000). See https://www.ffmpeg.org/ffmpeg.html#Description for a description of the solution.
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Interesting. Any idea if that's a new option (I've never noticed it before)? My only concern would be that it would break on some other version of ffmpeg. |
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Good point, I've actually first observed the error with FFMPEG v2.6, then updated to v2.8.1, where I've validated the proposed solution. I could double check on other versions, what is the lowest supported, or which versions should I cover? |
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On my CentOS6 machine, I see that the -r option is available and is documented to force a frame rate. Here is the version info: |
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And with |
| @@ -446,7 +446,7 @@ class FFMpegFileWriter(FileMovieWriter, FFMpegBase): | |||
| def _args(self): | |||
| # Returns the command line parameters for subprocess to use | |||
| # ffmpeg to create a movie using a collection of temp images | |||
| return [self.bin_path(), '-i', self._base_temp_name(), | |||
| return [self.bin_path(), '-r', str(self.fps), '-i', self._base_temp_name(), | |||
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Was wanting to double check when So, minus the pep8 issue, I'm 👍 on the change. As an aside, I really wish there were a better way to do this than to constantly tinker with the ffmpeg command line incantation. |
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It's also in the RHEL 5 man page (ffmpeg 0.5.2) Is a similar fix needed for the pipe based writer? |
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Looking at the pipe-based writer, I think it's already covered; the rate is set before the |
Ensure line length is <80.
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@dopplershift See #4416 😉 |
FIX: Force frame rate of FFMpegFileWriter input
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@auneri Thanks! |
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@tacaswell, @dopplershift, here is another one that has cost me hours of frustration. It is fixing a big bug, so I would like to backport it. In fact, from my reading of the avconv and ffmpeg docs (it applies to both), the second '-r' option is at best superfluous; the critical thing is to have the '-r' option specified before the '-i' option. Any '-r' option after the '-i' serves to drop or duplicate frames in an attempt to match the rate of the input. |
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👍 on backporting. |
FIX: Force frame rate of FFMpegFileWriter input
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Backported to v2.x as c0c65e3. |
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I am failing to see this change (or any change that addresses this issue) in master or 2.x, am I missing something? |
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Good catch. This is very puzzling. Some changes--not just this one--seem to have gone missing. I suspect something went wrong in all the backwards and forwards between v2.x and master. Or maybe I simply fouled it up myself. I will try to track it down. |
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I'm the culprit. Somehow, not long after merging this, I got mixed up and removed the wrong '-r'--and even left a comment in its place. I will fix it now. |
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OK, it should be fixed in v2.x and master now. Thanks for catching that, @auneri. |
The output video file was observed to skip frames, when input frame rate does not match output (e.g., when fps=1, or interval=1000).
See https://www.ffmpeg.org/ffmpeg.html#Description for a description of the solution.