Use
ffmpeg -i http://my-tv-stream.m3u8 -vf "select='eq(pict_type\,I)+eq(pict_type\,P)'" -vsync vfr -qscale:v 2 thumbnails-%02d.jpeg
Para enviar os tipos de quadros separadamente, use
ffmpeg -i http://my-tv-stream.m3u8 -vf "select='eq(pict_type\,I)" -vsync vfr -qscale:v 2 I-thumbnails-%02d.jpeg
-vf "select='eq(pict_type\,P)" -vsync vfr -qscale:v 2 P-thumbnails-%02d.jpeg