固定抽帧像素格式并收敛动作帧图像处理重复代码

ffmpeg 抽帧显式指定 -pix_fmt rgb24，消除 to_rgb8 截断 alpha 的隐患
抽出 compute_contain_dimensions 与 image_format_from_mime 供两条帧路径共用
尺寸已匹配时跳过无效的 Triangle 重采样

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server-rs/crates/api-server/src/character_animation_assets.rs

@@ -4287,6 +4287,8 @@ fn extract_video_frame_to_png(
             input_path.to_string_lossy().as_ref(),
             "-frames:v",
             "1",
+            "-pix_fmt",
+            "rgb24",
             "-f",
             "image2",
             output_path.to_string_lossy().as_ref(),
@@ -4386,13 +4388,7 @@ fn prepare_editor_character_animation_bgfilter_input(
     target_width: u32,
     target_height: u32,
 ) -> Result<FinalizedAnimationFrame, AppError> {
-    let image_format = match mime_type {
-        "image/png" => Some(ImageFormat::Png),
-        "image/jpeg" | "image/jpg" => Some(ImageFormat::Jpeg),
-        "image/webp" => Some(ImageFormat::WebP),
-        _ => None,
-    };
-    let image = match image_format {
+    let image = match image_format_from_mime(mime_type) {
         Some(format) => image::load_from_memory_with_format(source, format),
         None => image::load_from_memory(source),
     }
@@ -4404,19 +4400,13 @@ fn prepare_editor_character_animation_bgfilter_input(
     })?
     .to_rgb8();
 
-    let target_width = target_width.max(1);
-    let target_height = target_height.max(1);
-    let source_width = image.width().max(1);
-    let source_height = image.height().max(1);
-    let scale = (target_width as f32 / source_width as f32)
-        .min(target_height as f32 / source_height as f32);
-    let draw_width = ((source_width as f32 * scale).round() as u32)
-        .max(1)
-        .min(target_width);
-    let draw_height = ((source_height as f32 * scale).round() as u32)
-        .max(1)
-        .min(target_height);
-    let resized = image::imageops::resize(&image, draw_width, draw_height, FilterType::Triangle);
+    let (draw_width, draw_height) =
+        compute_contain_dimensions(image.width(), image.height(), target_width, target_height);
+    let resized = if (draw_width, draw_height) == (image.width(), image.height()) {
+        image
+    } else {
+        image::imageops::resize(&image, draw_width, draw_height, FilterType::Triangle)
+    };
 
     let mut encoded = Vec::new();
     let encoder = PngEncoder::new(&mut encoded);
@@ -4448,13 +4438,7 @@ fn finalize_animation_frame_payload(
     frame_height: u32,
     apply_chroma_key: bool,
 ) -> Result<FinalizedAnimationFrame, AppError> {
-    let image_format = match mime_type {
-        "image/png" => Some(ImageFormat::Png),
-        "image/jpeg" | "image/jpg" => Some(ImageFormat::Jpeg),
-        "image/webp" => Some(ImageFormat::WebP),
-        _ => None,
-    };
-    let mut image = match image_format {
+    let mut image = match image_format_from_mime(mime_type) {
         Some(format) => image::load_from_memory_with_format(source, format),
         None => image::load_from_memory(source),
     }
@@ -4501,8 +4485,39 @@ fn finalize_animation_frame_payload(
 
 fn contain_rgba_image(source: &RgbaImage, target_width: u32, target_height: u32) -> RgbaImage {
     let mut canvas = RgbaImage::from_pixel(target_width, target_height, Rgba([0, 0, 0, 0]));
-    let source_width = source.width().max(1);
-    let source_height = source.height().max(1);
+    let (draw_width, draw_height) =
+        compute_contain_dimensions(source.width(), source.height(), target_width, target_height);
+    let offset_x = ((target_width - draw_width) / 2) as i64;
+    let offset_y = ((target_height - draw_height) / 2) as i64;
+    if (draw_width, draw_height) == (source.width(), source.height()) {
+        image::imageops::overlay(&mut canvas, source, offset_x, offset_y);
+    } else {
+        let resized =
+            image::imageops::resize(source, draw_width, draw_height, FilterType::Triangle);
+        image::imageops::overlay(&mut canvas, &resized, offset_x, offset_y);
+    }
+    canvas
+}
+
+fn image_format_from_mime(mime_type: &str) -> Option<ImageFormat> {
+    match mime_type {
+        "image/png" => Some(ImageFormat::Png),
+        "image/jpeg" | "image/jpg" => Some(ImageFormat::Jpeg),
+        "image/webp" => Some(ImageFormat::WebP),
+        _ => None,
+    }
+}
+
+fn compute_contain_dimensions(
+    source_width: u32,
+    source_height: u32,
+    target_width: u32,
+    target_height: u32,
+) -> (u32, u32) {
+    let target_width = target_width.max(1);
+    let target_height = target_height.max(1);
+    let source_width = source_width.max(1);
+    let source_height = source_height.max(1);
     let scale = (target_width as f32 / source_width as f32)
         .min(target_height as f32 / source_height as f32);
     let draw_width = ((source_width as f32 * scale).round() as u32)
@@ -4511,11 +4526,7 @@ fn contain_rgba_image(source: &RgbaImage, target_width: u32, target_height: u32)
     let draw_height = ((source_height as f32 * scale).round() as u32)
         .max(1)
         .min(target_height);
-    let resized = image::imageops::resize(source, draw_width, draw_height, FilterType::Triangle);
-    let offset_x = ((target_width - draw_width) / 2) as i64;
-    let offset_y = ((target_height - draw_height) / 2) as i64;
-    image::imageops::overlay(&mut canvas, &resized, offset_x, offset_y);
-    canvas
+    (draw_width, draw_height)
 }
 
 async fn load_media_source_payload(