When displaying a frame count number in the drawtext filter, the varying height of the characters can make the text jitter vertically as they count. Its possible to stop this by applying the ‘ascent' value to the y coordinate.
However when the drawtext filter contains a box, this element also jitters vertically and there doesn’t appear to be a way to apply the same method of using the ‘ascent’ value to stabilise it.
Here is an example command (font is relevant to macOS):
In the above example, including ‘-ascent' in the y coordinate value stops the number characters from being jittery as they count. However you can see the box is still jittery and does not seem to support having the ‘-ascent’ value applied to it.
Is there any way to negate this jitter when using a box? Thanks.