ffmpeg limit number of images converted to video

You can use -frames:v:

ffmpeg -i img_%4d.jpg -frames:v 500 output.mp4

The -t option specifies the length of the output in either seconds or hh.mm.ss[.xxx] format (x=milliseconds) Alternatively the -to option sets the stop time, again in seconds or hh.mm.ss[.xxx] format

These are in the output options, rather than the input options btw.

More info at the ffmpeg documentation page, strangely enough.