Encoders are not always fully compatible with all image shapes

[hmaarrfk]

So we ran into this, and I figured I would share back some findings since I did contribute the code in question:

In recent version of imageio-ffmpeg, an attempt is made to find the "best" encoder.

imageio-ffmpeg/imageio_ffmpeg/_io.py

Line 16 in 7bfe71d

h264_encoder_preference["libx264"] = 100

However, the choice of encoder also needs to be conditioned, among other things, on the encoder capabilities.

Different things, like the pixel type, but most critically, the image shape, can affect the best choice for the given encoder.
See for example the bug report: https://trac.ffmpeg.org/ticket/9251

I've added a shape parameter to the test to ensure that the choice of encoder matches the shape of the video.

You probably also want to test with the compatibility of the filters. Though for me, this is outside the scope of my immediate needs.

[almarklein]

Thanks for reporting this. From what I understand some encoders may not support videos with a with/height smaller than 145 pixels. Do you know whether the limitations only relate to a minimum size or also e.g. factor of 2 constraints?

[hmaarrfk]

I figured that the cost of the test is small compared to the encoding time.

With users likely to encode under the same settings many times, the test, in conjunction with the shape as a tuple and lru cache, should amortize to 0 over the long run.

There i just test every time.