PyAV plugin always produces 480x640 when filters are specified

[djhoese]

I have some input data that depends on how the user sizes my GUI window so I can't guarantee things required by ffmpeg like frame sizes divisible by 2. To get around that I add a filter used by ffmpeg to scale the frame to the nearest 16 pixels. This is similar to what imageio-ffmpeg does to make frames consistent with the "macro block size".

When a filter is provided it seems that imageio/pyav always produces a video of 480x640 pixels instead of a size based on the input frames. From what I can tell the issue in the pyav plugin is that it provides the filters the video stream before it is full initialized during the frame writing. Is there a way around this?

import imageio.v3 as imageio
import numpy as np

imageio.imwrite("test.mp4", [np.zeros((512, 512, 3), dtype=np.uint8) for i in range(10)], plugin="pyav", codec="libx264")

imageio.imread("test.mp4", plugin="pyav").shape
# (10, 512, 512, 3)


imageio.imwrite("test.mp4", [np.zeros((512, 512, 3), dtype=np.uint8) for i in range(10)], plugin="pyav", codec="libx264", filter_sequence=[("scale", "iw+gt(mod(iw,16), 0)*(16-mod(iw,16)):ih+gt(mod(ih,16), 0)*(16-mod(ih,16))")])

imageio.imread("test.mp4", plugin="pyav").shape
# (10, 480, 640, 3)

[djhoese]

I was able to get this to work by swapping the if blocks here:

imageio/imageio/plugins/pyav.py

Lines 925 to 932 in 41a42a1

	if self._video_filter is not None:
	av_frame = self._video_filter.send(av_frame)
	if av_frame is None:
	return
	if stream.frames == 0:
	stream.width = av_frame.width
	stream.height = av_frame.height

But only in cases where my frame was already divisible by 2 (and possibly only when the filter didn't change the frame size). I think it is because the frame influences the stream size (width/height) but the stream influences how the filter behaves (chicken/egg problem).

[Ai-Himmel]

Seems to be #1003