"movie" of the 2d Rayleigh-Benard convection

[Jack]

Hi Dedalus Users,

There are online tools (such as http://gifmaker.me/) to make gif using images. Can the example code plot_2d_series.py

be adapted (easily?) to generate a "movie" of the 2d Rayleigh-Benard convection?

Jack

[Jeffrey S. Oishi]

Hi Jack,

Yes, though I'm not sure I fully understand your question. plot_2d_series.py outputs a series of png frames, which can be assembled into a movie at that site. You can also use something like ffmpeg on linux or mac, which you will have to install on your machine if you don't have it. I typically use ffmpeg to make movies like those you see at the dedalus vimeo site (https://vimeo.com/dedalus), though I think some mac users might use different programs.

Jeff

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[Jeffrey S. Oishi]

I should also add that ffmpeg has a LOT of options. Here's how I typically call it, using a little bash function written by Keaton. I just put this in my .bashrc, and then use that example to make a 30 frames per second movie. If you want a lower frame rate, just change the third argument to something like 15.

 PNG encoding with ffmpeg
# Example use: png2mp4 “frames/*" frames.mp4 30

# Options:
#   -y                  Overwrite output
#   -f image2pipe       Input format
#   -vcodec png         Input codec
#   -r $3               Frame rate
#   -i -                Input files from cat command
#   -f mp4              Output format
#   -vcodec libx264     Output codec
#   -pix_fmt yuv420p    Output pixel format
#   -preset slower      Prefer slower encoding / better results
#   -crf 20             Constant rate factor (lower for better quality)
#   -vf "scale..."      Round to even size
#   $2                  Output file
function png2mp4(){
    cat $1 | ffmpeg \
        -y \
        -f image2pipe \
        -vcodec png \
        -r $3 \
        -i - \
        -f mp4 \
        -vcodec libx264 \
        -pix_fmt yuv420p \
        -preset slower \
        -crf 20 \
        -vf "scale=trunc(in_w/2)*2:trunc(in_h/2)*2" \
        $2
}

[Yu Cao]

Hi Jeff, 

Once one has the outputs of plot_2d_series.py, one can use that site or ffmpeg to make movies. I was wondering if one can modify plot_2d_series.py so that

one directly gets a movie output. (It seems that there is no need to do so according to your comment.)

Jack

On Fri, Aug 3, 2018 at 11:05 AM Jeffrey S. Oishi <jso...@gmail.com> wrote:

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[Jeffrey S. Oishi]

Hi Jack,

Sure. Just put the call to ffmpeg in the python script using something like subprocess.run (https://docs.python.org/3/library/subprocess.html)

Jeff

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