When the screen is cut with long legs, the picture will shake or flicker, which is usually caused by the frame rate inconsistency between the newly inserted material and the original picture when the picture is lengthened.

To solve this problem, you can try the following methods:

1. Make sure that the newly inserted material has the same frame rate as the original picture. If the newly inserted material is slower than the original image, you can try to speed up; If the newly inserted material is faster than the original image, you can try to slow it down.

2. Adjust the duration of the elongated picture to make it consistent with the frame rate of the original picture. For example, if the original image is 5 seconds long and your extended image is 6 seconds long, you can try to adjust the extended image to 5 seconds to keep the frame rate consistent with the original image.

3. Add a transition effect in the silhouette to make the transition between the old and new images smoother. For example, you can try to add a transition effect such as gradient or rotation to reduce the feeling of jitter or flicker.

It should be noted that when adjusting the length of a long picture or adding a transition effect, it needs to be adjusted and modified according to the specific situation to achieve the best effect.