adding an ffmpeg.rs and thumbnailing fn

This module adds a bg_from_video function that takes uses the ffmpeg
binary to create thumbnails and adds them to the apps local data directory.

src/rust/ffmpeg.rs

@@ -0,0 +1,56 @@
+use dirs;
+use std::fs;
+use std::io::{self, Write};
+use std::path::{Path, PathBuf};
+use std::process::Command;
+use std::str;
+
+pub fn bg_from_video(video: &Path) -> PathBuf {
+    let video = PathBuf::from(video);
+    println!("{:?}", video);
+    println!("{:?}", video.file_name());
+    let mut data_dir = dirs::data_local_dir().unwrap();
+    data_dir.push("librepresenter");
+    data_dir.push("thumbnails");
+    if !data_dir.exists() {
+        fs::create_dir(&data_dir).expect("Could not create thumbnails dir");
+    }
+    let mut screenshot = data_dir.clone();
+    screenshot.push(video.file_name().unwrap());
+    screenshot.set_extension("png");
+    if !screenshot.exists() {
+        let output_duration = Command::new("ffprobe")
+            .args(&["-i", &video.to_string_lossy()])
+            .output()
+            .expect("failed to execute ffprobe");
+        let mut duration = String::from("");
+        let mut at_second: i32;
+        at_second = 2;
+        let mut log = str::from_utf8(&output_duration.stdout)
+            .expect("Using non UTF-8 characters")
+            .to_string();
+        if let Some(duration_index) = &log.find("Duration") {
+            duration = log.split_off(*duration_index + 10);
+            duration.truncate(11);
+            println!("rust-duration-is: {duration}");
+        }
+        let output = Command::new("ffmpeg")
+            .args(&[
+                "-i",
+                &video.to_string_lossy(),
+                "-ss",
+                &at_second.to_string(),
+                "-vframes",
+                "1",
+                "-y",
+                &screenshot.to_string_lossy(),
+            ])
+            .output()
+            .expect("failed to execute ffmpeg");
+        io::stdout().write_all(&output.stdout).unwrap();
+        io::stderr().write_all(&output.stderr).unwrap();
+    } else {
+        println!("Screenshot already exists");
+    }
+    screenshot
+}