Re: [matplotlib-devel] Strange bug when saving animations (with streamplot)

[Tony Yu <ts...@gm...>]

On Tue, Jul 3, 2012 at 11:18 AM, Ryan May <rm...@gm...> wrote:

> On Tue, Jul 3, 2012 at 10:03 AM, Tony Yu <ts...@gm...> wrote:
> >
> >
> > On Tue, Jul 3, 2012 at 10:22 AM, Ryan May <rm...@gm...> wrote:
> >>
> >> On Tue, Jul 3, 2012 at 9:14 AM, Tony Yu <ts...@gm...> wrote:
> >> > On Mon, Jul 2, 2012 at 11:42 PM, Tony Yu <ts...@gm...> wrote:
>
> >> >> 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
>
>
Hey Ryan,

I didn't see a PR for this issue, so I just added a fix:

https://github.com/matplotlib/matplotlib/pull/989

As mentioned before, the PR suppresses logging in ffmpeg under normal
circumstances. When the verbosity level is set to debug, however, the
subprocess output (stdout + stderr) are piped to `sys.stdout`. This is
where verbose reports are posted, so I figured that was the best place (oh,
actually, I guess could have piped to `verbose.fileo`).

If you feel the debug output should go to a file instead, let me know.

Cheers,
-Tony