The same resolution as the AVI video — a 1080p AVI produces 1920×1080 JPG frames; a 4K AVI produces 3840×2160 JPG frames. Use the resize utility after extraction if you want smaller thumbnails or social-media-sized crops.
קען איך אױסשטעלן װײַל װיפֿל ראָמען פֿון AVI װי JPG?