diff --git a/dcc/concat.py b/dcc/concat.py
new file mode 100644
index 0000000..46df15a
--- /dev/null
+++ b/dcc/concat.py
@@ -0,0 +1,119 @@
+import av
+import copy
+import dcc.doom_base
+import fractions
+import io
+import logging
+import math
+import numpy as np
+import wand.image
+
+class Concat(dcc.doom_base.Wad):
+	def get_parser(self, prog_name):
+		parser = super().get_parser(prog_name)
+		parser.add_argument("start_map")
+		parser.add_argument("end_map")
+		return parser
+
+	def take_action(self, parsed_args):
+		logging.basicConfig()
+		av.logging.set_level(av.logging.VERBOSE)
+		av.logging.restore_default_callback()
+		videos = self.fabricate.joinpath(parsed_args.wad).glob(f"{parsed_args.wad}_map*.mp4")
+		output = av.open(self.fabricate.joinpath(parsed_args.wad).joinpath(f"{parsed_args.wad}_maps{parsed_args.start_map}to{parsed_args.end_map}.mp4"), "w")
+		offset = 0
+		# We'd like to use the concat filter here and connect everything into a
+		# single filter graph... but it produces a "Resource temporarily
+		# unavailable" error when switching to inputs after the first.  Presumably
+		# fixable, but it's easier to just make one graph per video and mux
+		# everything together at the end.
+		for v in sorted(videos):
+			# TODO: Support UDoom in literally any way.
+			if not (v.name >= f"{parsed_args.wad}_map{parsed_args.start_map}.mp4" and
+				v.name <= f"{parsed_args.wad}_map{parsed_args.end_map}.mp4"):
+				continue
+
+			chunk = av.open(v)
+			ograph = av.filter.Graph()
+			sink = ograph.add("buffersink")
+			asink = ograph.add("abuffersink")
+
+			img = wand.image.Image(height=chunk.streams[0].height,width=chunk.streams[0].width)
+			mapstring = v.name[-6:-4]
+			text = self._config["map_names"][f"map{mapstring}"]
+			dcc.text.draw_text(img, f"MAP{mapstring}: {text}", font_size=120)
+			img.trim(reset_coords=True)
+			img.border("graya(25%, 25%)", 10, 10)
+			img.border(dcc.config.TEXT_STROKE_COLOR, 16, 16)
+			# for this to work... the image needs to have a width that's a multiple
+			# of 8.  dude whyyyyyyy
+			padfactor=8
+			img.border("transparent", padfactor, 0)
+			img.crop(width=img.width-img.width%padfactor, height=img.height)
+			text_frame = av.video.frame.VideoFrame(img.width, img.height, format="rgba")
+
+			if len(output.streams.get()) == 0:
+				# TODO: less hardcoding.
+				output.add_stream("h264", rate=61440)
+				output.streams[0].extradata = copy.deepcopy(chunk.streams[0].extradata)
+				output.streams[0].height=1440
+				output.streams[0].width=2560
+				output.streams[0].profile="High"
+				output.streams[0].qmax = chunk.streams[0].qmax
+				output.streams[0].qmin = chunk.streams[0].qmin
+				output.streams[0].codec_context.gop_size=30
+				output.streams[0].codec_context.max_b_frames=2
+				output.streams[0].codec_context.framerate = fractions.Fraction(60,1)
+				output.streams[0].codec_context.pix_fmt="yuv420p"
+				output.streams[0].codec_context.bit_rate = chunk.streams[0].codec_context.bit_rate
+				output.add_stream("aac", rate=48000)
+				output.streams[1].extradata = copy.deepcopy(output.streams[1].extradata)
+				output.streams[1].rate=48000
+				output.streams[1].bit_rate=chunk.streams[1].bit_rate
+			src = ograph.add_buffer(template=chunk.streams[0], time_base=chunk.streams[0].time_base)
+			asrc = ograph.add_abuffer(template=chunk.streams[1], time_base=chunk.streams[1].time_base)
+			overlay = ograph.add_buffer(width=img.width, height=img.height, format="rgba", time_base=chunk.streams[0].time_base)
+			overlay_fo = ograph.add("fade", args="out:240:60")
+			overlay.link_to(overlay_fo, 0, 0)
+			composite = ograph.add("overlay", args="x=4:y=4")
+			src.link_to(composite, 0, 0)
+			overlay_fo.link_to(composite, 0, 1)
+			ifade = ograph.add("fade", args="in:0:60")
+			iafade = ograph.add("afade", args="in:{}:48000".format(offset*48000/1000000))
+			ofade = ograph.add("fade", args="out:{}:60".format((chunk.duration*60/1000000)-60))
+			oafade = ograph.add("afade", args="out:{}:48000".format(((offset+chunk.duration)*48000/1000000)-48000))
+			composite.link_to(ifade, 0, 0)
+			asrc.link_to(iafade, 0, 0)
+			ifade.link_to(ofade, 0, 0)
+			iafade.link_to(oafade, 0, 0)
+			ofade.link_to(sink, 0, 0)
+			oafade.link_to(asink, 0, 0)
+
+			ograph.configure()
+			for packet in chunk.demux():
+				if packet.dts is None:
+					continue
+				packet.dts += (offset * packet.time_base.denominator) / (packet.time_base.numerator * 1000000)
+				packet.pts += (offset * packet.time_base.denominator) / (packet.time_base.numerator * 1000000)
+				if packet.stream_index == 0:  # TODO: robustness
+					for ifr in packet.decode():
+						text_frame = av.video.frame.VideoFrame(img.width, img.height, format="rgba")
+						text_frame.planes[0].update(img.make_blob(format="rgba"))
+						text_frame.pts = ifr.pts
+						text_frame.dts = ifr.dts
+						text_frame.time_base = ifr.time_base
+						overlay.push(text_frame)
+						src.push(ifr)
+						ofr = sink.pull()
+						for p in output.streams[packet.stream_index].encode(ofr):
+							output.mux(p)
+				else:
+					for ifr in packet.decode():
+						asrc.push(ifr)
+						ofr = asink.pull()
+						for p in output.streams[packet.stream_index].encode(ofr):
+							output.mux(p)
+			offset += chunk.duration
+			chunk.close()
+		output.close()
+