File formats : 
gif, jpeg, png, HTML5, and 3rd party tags (HTTPs compliant only)

Creative weight:
gif, jpeg, png - 50kb (970x250 is 100k)HTML 5 – 50k mobile, 140k desktop / tablet

Adspecs Skin

Top margin
Start image 50 pixels from top of page for site header.
Left/Right margin
130 pixels
Maximum creative weight
150kb
File format
gif, jpeg or png