trimming video with FFMPEG, but the output is a black video, with audio

i have a video, and i want to trim it. This is what I am doing:

ffmpeg -i input.mp4 -ss 0 -t 4 -vcodec copy -acodec copy output.mp4

However, output.mp4 only provides me with the correct audio -- the video is just a black screen

I found a similar issue, and someone said to add -pix_fmt yuv420p I added it, but nothing changed (did i add it incorrectly?)

Any thoughts?