arecord, convert: edit pages

pages/common/convert.md

@@ -16,13 +16,13 @@
 
 `convert {{path/to/input_image.png}} -resize 640x480 {{path/to/output_image.png}}`
 
-- Horizontally append images:
+- Scale an image to have a specified file size:
 
-`convert {{path/to/image1.png path/to/image2.png ...}} +append {{path/to/output_image.png}}`
+`convert {{path/to/input_image.png}} -define jpeg:extent=512kb {{path/to/output_image.jpg}}`
 
-- Vertically append images:
+- Vertically/Horizontally append images:
 
-`convert {{path/to/image1.png path/to/image2.png ...}} -append {{path/to/output_image.png}}`
+`convert {{path/to/image1.png path/to/image2.png ...}} {{-append|+append}} {{path/to/output_image.png}}`
 
 - Create a GIF from a series of images with 100ms delay between them:
 

pages/linux/arecord.md

@@ -22,3 +22,7 @@
 - Allow interactive interface (e.g. use space-bar or enter to play or pause):
 
 `arecord --interactive`
+
+- Test your microphone by recording a 5 second sample and playing it back:
+
+`arecord -d 5 test-mic.wav && aplay test-mic.wav && rm test-mic.wav`