Bug report

Bug summary

Saving an animation with 1000 frames to a mp4 file via the ffmpeg writer fails on matplotlib 2.2. Instead of the desired 1000 frames, only some 300 frames are saved, then the process stops.
The same code works fine on matplotlib 2.1.

Code for reproduction

The following is the example code from basic_example_writer, with the number of frames modified to 1000.

import matplotlib
matplotlib.use("Agg")
print matplotlib.__version__
import matplotlib.pyplot as plt
import matplotlib.animation as animation

def update_line(num, data, line):
    line.set_data(data[..., :num])
    print num
    return line,

# Set up formatting for the movie files
Writer = animation.writers['ffmpeg']
writer = Writer(fps=15, metadata=dict(artist='Me'), bitrate=1800)  # try -1 as well

fig1 = plt.figure()

data = np.random.rand(2, 1000)
l, = plt.plot([], [], 'r-')
plt.xlim(0, 1)
plt.ylim(0, 1)
plt.xlabel('x')
plt.title('test')
line_ani = animation.FuncAnimation(fig1, update_line, 1000, fargs=(data, l),
                                   interval=50, blit=True)
line_ani.save('lines.mp4', writer=writer)

Actual outcome

In matplotlib 2.2 this code prints the numbers up to some endnumber of around 290. Then nothing happens - i.e. the process does not finish, just halts. There is a mp4 file created which shows those first 290 frames correctly (0:20 min long video). This file is created after the running process is manually termined.
Creating an animated gif via the imagemagick writer is perfectly possible though.

Expected outcome

In matplotlib 2.1 the code produces an mp4 file with 1000 frames (i.e. a 1:06 min long video) as expected.

Further details
Some relevant rcParams here:

print plt.rcParams["savefig.bbox"]           # None
print plt.rcParams["animation.writer"]       # ffmpeg
print plt.rcParams["animation.codec"]        # h264
print plt.rcParams["animation.ffmpeg_path"]  # ffmpeg
print plt.rcParams["animation.ffmpeg_args"]  # []

They are the same in both cases.

The actual number of frames produces varies. It is depending on the bitrate. 5 successive runs produce

with bitrate 1800
295, 293, 290, 291, 293  frames

bitrate -1 (default)
311, 311, 311, 311, 305  frames

This issue has been brought up in this SO post. In that case the example uses images and the maximal number of frames is again different from this example here.

Matplotlib version

• Operating system: Windows 8.1
• Matplotlib version: 2.2 (for nonworking code), 2.1 (for working code)
• Matplotlib backend : Agg
• Python version: 2.7.10
• Other libraries: ffmpeg 2.8.4 (built with gcc 5.2)