Finished explantion comments

src/out.rs

@@ -46,25 +46,27 @@ pub fn print_square(frame: &ffmpeg::frame::Video, lines_format: LinesFormat, vid
     let mut stdout = stdout();
     let mut lock = stdout.lock();
 
-    // Entire frame, as rgb data
-    let buf = frame.data(video_index); 
-
-    // How many bytes per line
-    let step = buf.len() / frame.height() as usize;
-
-    // Explanation?: (12x12 image:)
+    // EXPLANATION: (12x12 image)
     // The full buffer will be 1152 bytes.
+    //
     // 1152/12=96   Buffer length   / Pixels high       = 96 Bytes per line.
     // 96/12=8      Bytes per line  / Pixels per line   = 8 Bytes per pixel.
     //
-    // But RGB24 should only use 3 bytes per pixel.
-    // The other 5 we just discard.
+    // But RGB24 should only use 3 bytes per pixel. The other 5 we just discard.
+    // They might be alpha, or grayscale overlay, I'm not really sure.
     //
+    // 8-5=3        Bytes per pixel - Discarded bytes = Used bytes
+    // 3*12=36      Used bytes      * Pixels per line = Slice length
+    //
+    // This is because all the extra data (the 5 extra bytes) are at the end
+    // of each line. So we just take the first (Pixel width)*3 bytes.
+
+    let buf = frame.data(video_index); 
+    let step = buf.len() / frame.height() as usize;
 
     // (Assuming square) Step thru buffer.
     for i in 0..pixels_wide {
         let j = i*step;
-        // Only take the size*3 of bytes, ignoring alpha(?) values which are stored after.
         // Have to take ownership, by implicilty Cloning the data. (Copying?)
         let mut slice = Vec::from(&buf[j..j+pixels_wide*3]);