regression when writing m4v via ffmpeg/avconv (convert: delegate failed `'avconv' -nostdin ...)

[tacaswell]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am using the latest version of ImageMagick
• I have searched open and closed issues to ensure it has not already been reported

Description

We found this regression via the Matplotlib test suite so apologies for the Matplotlib/python components of this bug report.

We use subprocess to call convert (which in turns ffmeg/avconv) and then pipe rgba formatted buffers to the process to save animations.

This worked with 7.0.10-31 and fails with 7.0.10-34.

link to it faliing in our CI: https://dev.azure.com/matplotlib/matplotlib/_build/results?buildId=15079&view=logs&j=9878844f-86f0-56ff-f1e1-852bef74b1f7&t=545d203d-ae00-54f9-05d7-a7d9813d4088&l=203

Steps to Reproduce

✔ 13:02:38 $ convert -size 800x600 -depth 8 -delay 20.0 -loop 0 /tmp/test.png /tmp/temp.m4v                                                                                                                                                                                                            
convert: delegate failed `'avconv' -nostdin -v -1 -i '%M%%d.pam' -plays %I '%u.%m' 2> '%u'' @ error/delegate.c/InvokeDelegate/1898.

A simplified version of what Matplotlib does internally

This is a simpler version of what the test suite is doing:

In [1]: import subprocess

In [2]: import matplotlib.pyplot as plt

In [3]: import matplotlib

In [4]: matplotlib.use('agg')

In [5]: fig, ax = plt.subplots(figsize=(8, 6))

In [6]: cmd = ('convert', '-size', '800x600', '-depth', '8', '-delay', '20.0', '-loop', '0', 'rgba:-', '/tmp/temp2.m4v')

In [7]: PIPE = subprocess.PIPE

In [8]: proc = subprocess.Popen(cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE)

In [9]: fig.savefig(proc.stdin, format='rgba')

In [10]: proc.communicate()
Out[10]: 
(b'',
 b"convert: delegate failed `'avconv' -nostdin -v -1 -i '%M%%d.pam' -plays %I '%u.%m' 2> '%u'' @ error/delegate.c/InvokeDelegate/1898.\n")

Can produce this on mac and linux (both py38).

System Configuration

• ImageMagick version: 7.0.10-34
• Environment (Operating system, version and so on): OSX (catalina), linux (arch)
• Additional information: ffmpeg must also be installed

[xordux]

I can produce same error in Windows system as well:

(test_env) C:\PersonalProjects>"C:\Program Files\ImageMagick-7.0.10-Q16-HDRI\convert" -size 800x600 -depth 8 -delay 20.0 -loop 0 tmp.png temp.m4v
convert: delegate failed `"ffmpeg.exe" -nostdin -v -1 -i "%M%%d.pam" -plays %I "%u.%m" 2> "%u"' @ error/delegate.c/InvokeDelegate/1898.

System Configuration:

• ImageMagick version: ImageMagick 7.0.10-34 Q16 x64 2020-10-08
• Environment (Operating system, version and so on): Windows10
• Additional information: ffmpeg is also installed

[urban-warrior]

Thanks for the problem report. We can reproduce it and will have a patch to fix it in the GIT master branch @ https://github.com/ImageMagick/ImageMagick later today. The patch will be available in the beta releases of ImageMagick @ https://www.imagemagick.org/download/beta/ by sometime tomorrow.

[tacaswell]

@urban-warrior Awesome! Thank you for the super fast turn around!