We use any server to upload video and it returns a thumbnail file that was made by lavc. Erl_img returns this error when:

{ok, Magic} = erl_img:magic_info(File)

Reason: error:undef, [{video_mpeg,magic,[<<255,216,255,254,0,16,76,97,118,99,53,52,46,57,50,46,49,48,48,0,255,219,0,67,0,8,10,10,11,10,11,13,13,13,13,13,13,16,15,16,16,16,16,16,16,16,16,16,16,16,18,18,18,21,21,21,18,18,18,16,16,18,18,20>>],[]},{erl_img,magic,2,[{file,"src/erl_img.erl"},{line,43}]},{erl_img,read_magic_info,1,[{file,"src/erl_img.erl"},{line,69}]},{erl_img,magic_info,1,[{file,"src/erl_img.erl"},{line,83}]}, ...]