add more details

README.md

@@ -1,5 +1,32 @@
 # milkbucket
 
+## Build
+milkbucket depends on the
+[projectM](https://github.com/projectM-visualizer/projectm) library. To run
+milkbucket, you'll need to install this library either by building it yourself,
+or installing one of the builds from
+[here](https://github.com/projectM-visualizer/projectm/actions). (If you've
+never done this before, you'll want to download one of the "shared" artifacts
+for your system. Then, copy the contents of the artifact's `include` folder to
+`/usr/local/include` and the contents of the `lib` folder to `/usr/local/lib`.)
+
+After installing projectM, build milkbucket with `go build`.
+
+## Usage
+milkbucket reads a PCM stream from standard input to generate visualizations.
+If you have an audio file and a preset in mind, you can use `ffmpeg` to
+generate the PCM stream, then pipe to milkbucket, like so:
+```
+ffmpeg -i $audio -ar 44100 -f s16le - | ./milkbucket -p $preset
+```
+
+Note that neither of these commands will output any audio! If you want to hear the audio at the same time (and assuming your machine uses pipewire), run:
 ```
 ffmpeg -i $audio -ar 44100 -f s16le - | tee >(pw-play --rate=44100 --format=s16 -) | ./milkbucket -p $preset
 ```
+(If you don't use pipewire try using `aplay` instead of `pw-play`, or some other command for playing PCM streams.)
+
+You can also generate a visualization from your system sound. Assuming pipewire again, and that you have audio coming from Firefox, run:
+```
+pw-record --target Firefox - | ./milkbucket -p $preset
+```

cmd/root.go

@@ -17,6 +17,7 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 package cmd
 
 import (
+	"log"
 	"os"
 
 	"github.com/spf13/cobra"
@@ -46,7 +47,16 @@ func handleEvent(event sdl.Event, m *milkDropWindow) bool {
 }
 
 func milkbucket(cmd *cobra.Command, args []string) {
-	err := sdl.Init(sdl.INIT_VIDEO)
+	fi, err := os.Stdin.Stat()
+	if err != nil {
+		panic(err)
+	}
+	size := fi.Size()
+	if size <= 0 {
+		log.Fatal("stdin is empty")
+	}
+
+	err = sdl.Init(sdl.INIT_VIDEO)
 	if err != nil {
 		panic(err)
 	}