add compress-video script for reducing video size

modules/home/cli/terminal.nix

@@ -59,6 +59,7 @@ in
 
     gnupg
     ffmpeg
+    compress-video
   ];
 
   fonts.fontconfig.enable = true;

packages/compress-video.nix

@@ -0,0 +1,54 @@
+{ writeShellApplication, ffmpeg-full, ... }:
+
+writeShellApplication {
+  name = "compress-video";
+  meta.description = ''
+    Compress a video file for sharing (e.g., Slack's 1GB limit).
+    Usage: compress-video input.mov [target_size_mb]
+    Default target size is 900MB.
+  '';
+  runtimeInputs = [ ffmpeg-full ];
+  text = ''
+    input="$1"
+    target_mb="''${2:-900}"
+
+    if [ -z "$input" ]; then
+      echo "Usage: compress-video <input> [target_size_mb]"
+      exit 1
+    fi
+
+    output="''${input%.*}-compressed.mp4"
+
+    # Get duration in seconds
+    duration=$(ffprobe -v error -show_entries format=duration -of csv=p=0 "$input")
+    duration_int="''${duration%%.*}"
+
+    # Calculate target bitrate (bits/sec) = target_bytes * 8 / duration
+    # Reserve ~128kbps for audio
+    audio_bitrate=128
+    total_bitrate=$(( (target_mb * 8192) / duration_int ))
+    video_bitrate=$(( total_bitrate - audio_bitrate ))
+
+    if [ "$video_bitrate" -lt 500 ]; then
+      echo "Warning: video is too long for target size. Bitrate would be very low."
+      echo "Consider a smaller target or trimming the video."
+      video_bitrate=500
+    fi
+
+    echo "Input:  $input"
+    echo "Output: $output"
+    echo "Duration: ''${duration_int}s"
+    echo "Target: ''${target_mb}MB → video bitrate: ''${video_bitrate}k"
+
+    ffmpeg -i "$input" \
+      -c:v libx264 -b:v "''${video_bitrate}k" \
+      -c:a aac -b:a "''${audio_bitrate}k" \
+      -movflags +faststart \
+      "$output"
+
+    input_size=$(stat --printf="%s" "$input" 2>/dev/null || stat -f "%z" "$input")
+    output_size=$(stat --printf="%s" "$output" 2>/dev/null || stat -f "%z" "$output")
+    echo ""
+    echo "Done: $(( input_size / 1048576 ))MB → $(( output_size / 1048576 ))MB"
+  '';
+}