Format Options:
-F or --render-format <format>
Set the render format, Valid options are...
    TGA IRIS JPEG MOVIE IRIZ RAWTGA
    AVIRAW AVIJPEG PNG BMP FRAMESERVER
(formats that can be compiled into blender, not available on all systems)
    HDR TIFF EXR MULTILAYER MPEG AVICODEC QUICKTIME CINEON DPX DDS

blender --background /path/to/file.blend --python /path/to/script.py --render-anim

blender -b /path/to/file.blend -P /path/to/script.py -a

for scene in bpy.data.scenes:
    scene.render.resolution_x = 1920
    scene.render.resolution_y = 1080
    scene.render.image_settings.file_format = 'H264'