This allows the following usages:
FFMPEG_DATADIR=presets ./ffmpeg -f lavfi -i testsrc=d=5 -vcodec libx264 -vpre ipod640 -f null -
FFMPEG_DATADIR=presets ./ffmpeg -f lavfi -i testsrc=d=5 -vpre libx264-ipod640 -f null -
The second example was broken even if documented.
+vcodec=libvpx
+
g=120
lag-in-frames=16
deadline=good
+vcodec=libvpx
+
g=120
lag-in-frames=25
deadline=good
+vcodec=libvpx
+
g=120
lag-in-frames=16
deadline=good
+vcodec=libvpx
+
g=120
lag-in-frames=16
deadline=good
+vcodec=libvpx
+
g=120
lag-in-frames=25
deadline=good
+vcodec=libx264
+
vprofile=baseline
level=13
maxrate=768000
+vcodec=libx264
+
vprofile=baseline
level=30
maxrate=10000000