On Tue, Jul 3, 2012 at 10:03 AM, Tony Yu <tsy...@gmail.com> wrote:
>
>
> On Tue, Jul 3, 2012 at 10:22 AM, Ryan May <rma...@gmail.com> wrote:
>>
>> On Tue, Jul 3, 2012 at 9:14 AM, Tony Yu <tsy...@gmail.com> wrote:
>> > On Mon, Jul 2, 2012 at 11:42 PM, Tony Yu <tsy...@gmail.com> wrote:
>> >> On Sun, Jun 24, 2012 at 10:02 AM, Tony Yu <tsy...@gmail.com> wrote:
>> >>>
>> >>> I'm having a tough time figuring this out: Saving an animation seems
>> >>> to
>> >>> hang when using `streamplot`. The exact same animation runs without
>> >>> issue
>> >>> when calling show.
>> >>>
>> >>> On my system, the example below hangs consistently at frame 173.
>> >>> However,
>> >>> the number of saved frames (before hanging) varies with density of
>> >>> stream
>> >>> lines (i.e. number of line segments in streamplot): More frames saved
>> >>> for
>> >>> lower density.
>> >>>
>> >>> Seems to be a memory or file-size issue, but
>> >>>
>> >>> * Memory use doesn't seem to grow. (this suggests that ffmpeg adds
>> >>> frames to disk as opposed to memory.)
>> >>> * Saving the animation up to the frame just before it hangs gives
>> >>> modest (~1MB) videos.
>> >>> Maybe this is a limitation of `ffmpeg`?
>> >>>
>> >>> Can someone confirm that the example hangs on their system? (Somehow,
>> >>> I
>> >>> often run into bugs that are not reproducible.)
>> >>>
>> >>> In case this is system dependent:
>> >>> * OSX 10.6
>> >>> * Python 2.6.1 (system install)
>> >>> * matplotlib master
>> >>> * ffmpeg 0.10
>> >>>
>> >>> Simple plots seem to work fine, but I should probably try to reproduce
>> >>> using something other than streamplot (maybe create the equivalent
>> >>> number of
>> >>> line and arrow collections).
>> >>>
>> >>> -Tony
>> >>>
>> >>> #~~~ Example
>> >>> import numpy as np
>> >>> import matplotlib.pyplot as plt
>> >>> import matplotlib.animation as animation
>> >>>
>> >>> fig, ax = plt.subplots()
>> >>>
>> >>> # do nothing function that prints frame
>> >>> def update(frame_num):
>> >>> print frame_num
>> >>> return []
>> >>>
>> >>> Y, X = np.mgrid[:1:100j, :1:100j]
>> >>> U = np.ones_like(X)
>> >>> V = np.ones_like(X)
>> >>> ax.streamplot(X, Y, U, V, density=1)
>> >>>
>> >>> ani = animation.FuncAnimation(fig, update, save_count=500)
>> >>>
>> >>> # save hangs at frame 173 (this probably varies by system, if it's
>> >>> reproducible).
>> >>> ani.save('animation.avi')
>> >>> # show animates all frames w/o issue.
>> >>> #plt.show()
>> >>>
>> >>>
>> >>
>> >> I finally had some time to revisit this issue. It seems that subprocess
>> >> PIPEs have fairly limited buffers [1] (also see docs for
>> >> `subprocess.Popen.communicate` [2]) and ffmpeg tends to generate a
>> >> decent
>> >> amount of output to stderr. A simple solution is to redirect stderr to
>> >> a
>> >> temporary file. This change fixes the issue on my system.
>> >>
>> >> If this bug is reproducible, I can submit a PR. The temporary file here
>> >> could be created using tempfile so it gets cleaned up automatically, or
>> >> maybe a more permanent log file for debugging. Thoughts?
>> >>
>> >> -Tony
>> >>
>> >> [1]
>> >>
>> >> http://thraxil.org/users/anders/posts/2008/03/13/Subprocess-Hanging-PIPE-is-your-enemy/
>> >>
>> >> [2]
>> >>
>> >> http://docs.python.org/library/subprocess.html#subprocess.Popen.communicate
>> >>
>> >
>> > And just to clarify: My original email mentioned that saving would hang
>> > only
>> > when `streamplot` was used to create the figure. It turns out that
>> > ffmpeg
>> > prints more output (keyframes?) for more complex images, so when I ran
>> > simpler plots, they didn't produce enough output to fill the subprocess
>> > `PIPE` (although they would eventually).
>> >
>> > Also, theres's a simpler fix than piping ffmpeg output to a file: Just
>> > set
>> > `-loglevel quiet` in the ffmpeg command.
>> >
>> > -Tony
>>
>> It's not a bad idea to have it logged to a file in a temp directory.
>> We could potentially just do this if debug is set to verbose, however,
>> and just use -loglevel quiet otherwise. Can you manage PR for this or
>> do I need to?
>>
>> Ryan
>>
>
> Hey Ryan,
>
> If you have time, that'd be great. Otherwise, I should have some time at the
> end of the week to submit a PR.
>
> -Tony
>
I might be able to squeeze it in. If you don't see anything by the end
of the week, hit me up.
Ryan
--
Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma
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