diff --git a/mediarepo-api/Cargo.toml b/mediarepo-api/Cargo.toml
index ce2ebd9c..172fe84d 100644
--- a/mediarepo-api/Cargo.toml
+++ b/mediarepo-api/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "mediarepo-api"
-version = "0.29.0"
+version = "0.30.0"
 edition = "2018"
 license = "gpl-3"
 
diff --git a/mediarepo-api/src/client_api/job.rs b/mediarepo-api/src/client_api/job.rs
index f338d420..cfbe8d14 100644
--- a/mediarepo-api/src/client_api/job.rs
+++ b/mediarepo-api/src/client_api/job.rs
@@ -26,17 +26,11 @@ impl JobApi {
 
     /// Runs a job of the given type and returns when it has finished
     #[tracing::instrument(level = "debug", skip(self))]
-    pub async fn run_job(&self, job_type: JobType) -> ApiResult<()> {
-        self.emit(
-            "run_job",
-            RunJobRequest {
-                job_type,
-                sync: true,
-            },
-        )
-        .await_reply()
-        .with_timeout(Duration::from_secs(3600))
-        .await?;
+    pub async fn run_job(&self, job_type: JobType, sync: bool) -> ApiResult<()> {
+        self.emit("run_job", RunJobRequest { job_type, sync })
+            .await_reply()
+            .with_timeout(Duration::from_secs(3600))
+            .await?;
 
         Ok(())
     }
diff --git a/mediarepo-api/src/tauri_plugin/commands/job.rs b/mediarepo-api/src/tauri_plugin/commands/job.rs
index 8866b8b5..313e613a 100644
--- a/mediarepo-api/src/tauri_plugin/commands/job.rs
+++ b/mediarepo-api/src/tauri_plugin/commands/job.rs
@@ -3,9 +3,9 @@ use crate::tauri_plugin::error::PluginResult;
 use crate::types::jobs::JobType;
 
 #[tauri::command]
-pub async fn run_job(api_state: ApiAccess<'_>, job_type: JobType) -> PluginResult<()> {
+pub async fn run_job(api_state: ApiAccess<'_>, job_type: JobType, sync: bool) -> PluginResult<()> {
     let api = api_state.api().await?;
-    api.job.run_job(job_type).await?;
+    api.job.run_job(job_type, sync).await?;
 
     Ok(())
 }
diff --git a/mediarepo-api/src/tauri_plugin/custom_schemes.rs b/mediarepo-api/src/tauri_plugin/custom_schemes.rs
index 436b8f47..41e458de 100644
--- a/mediarepo-api/src/tauri_plugin/custom_schemes.rs
+++ b/mediarepo-api/src/tauri_plugin/custom_schemes.rs
@@ -122,8 +122,8 @@ async fn thumb_scheme<R: Runtime>(app: &AppHandle<R>, request: &Request) -> Resu
             .file
             .get_thumbnail_of_size(
                 FileIdentifier::CD(hash.to_string()),
-                ((height as f32 * 0.8) as u32, (width as f32 * 0.8) as u32),
-                ((height as f32 * 1.2) as u32, (width as f32 * 1.2) as u32),
+                ((height as f32 * 0.5) as u32, (width as f32 * 0.5) as u32),
+                ((height as f32 * 1.5) as u32, (width as f32 * 1.5) as u32),
             )
             .await?;
         tracing::debug!("Received {} content bytes", bytes.len());
diff --git a/mediarepo-api/src/types/jobs.rs b/mediarepo-api/src/types/jobs.rs
index e8b9d3bc..6cbed1a9 100644
--- a/mediarepo-api/src/types/jobs.rs
+++ b/mediarepo-api/src/types/jobs.rs
@@ -10,6 +10,7 @@ pub struct RunJobRequest {
 pub enum JobType {
     MigrateContentDescriptors,
     CalculateSizes,
+    GenerateThumbnails,
     CheckIntegrity,
     Vacuum,
 }
diff --git a/mediarepo-daemon/Cargo.lock b/mediarepo-daemon/Cargo.lock
index 58ccaee3..019f5867 100644
--- a/mediarepo-daemon/Cargo.lock
+++ b/mediarepo-daemon/Cargo.lock
@@ -1361,7 +1361,7 @@ checksum = "a3e378b66a060d48947b590737b30a1be76706c8dd7b8ba0f2fe3989c68a853f"
 
 [[package]]
 name = "mediarepo-api"
-version = "0.29.0"
+version = "0.30.0"
 dependencies = [
  "bromine",
  "chrono",
diff --git a/mediarepo-daemon/mediarepo-logic/src/dao/job/generate_missing_thumbnails.rs b/mediarepo-daemon/mediarepo-logic/src/dao/job/generate_missing_thumbnails.rs
new file mode 100644
index 00000000..edc84d98
--- /dev/null
+++ b/mediarepo-daemon/mediarepo-logic/src/dao/job/generate_missing_thumbnails.rs
@@ -0,0 +1,30 @@
+use crate::dao::job::JobDao;
+use crate::dao::DaoProvider;
+use mediarepo_core::error::RepoResult;
+use mediarepo_core::futures;
+use mediarepo_core::thumbnailer::ThumbnailSize;
+
+impl JobDao {
+    /// Generates thumbnails for files that are still missing some
+    #[tracing::instrument(level = "debug", skip(self))]
+    pub async fn generate_missing_thumbnails(&self) -> RepoResult<()> {
+        let file_dao = self.file();
+        let files = file_dao.all().await?;
+        let mut missing_thumbnails = Vec::new();
+
+        for file in files {
+            if file_dao.thumbnails(file.encoded_cd()).await?.is_empty() {
+                missing_thumbnails.push(file);
+            }
+        }
+
+        futures::future::join_all(missing_thumbnails.into_iter().map(|f| async {
+            file_dao
+                .create_thumbnails(f, vec![ThumbnailSize::Medium])
+                .await
+        }))
+        .await;
+
+        Ok(())
+    }
+}
diff --git a/mediarepo-daemon/mediarepo-logic/src/dao/job/mod.rs b/mediarepo-daemon/mediarepo-logic/src/dao/job/mod.rs
index 16bace31..31ab2907 100644
--- a/mediarepo-daemon/mediarepo-logic/src/dao/job/mod.rs
+++ b/mediarepo-daemon/mediarepo-logic/src/dao/job/mod.rs
@@ -1,5 +1,6 @@
 use crate::dao_provider;
 
+pub mod generate_missing_thumbnails;
 pub mod migrate_content_descriptors;
 pub mod sqlite_operations;
 
diff --git a/mediarepo-daemon/mediarepo-socket/src/namespaces/jobs.rs b/mediarepo-daemon/mediarepo-socket/src/namespaces/jobs.rs
index 3a31cdf0..c912b706 100644
--- a/mediarepo-daemon/mediarepo-socket/src/namespaces/jobs.rs
+++ b/mediarepo-daemon/mediarepo-socket/src/namespaces/jobs.rs
@@ -27,11 +27,17 @@ impl JobsNamespace {
         let run_request = event.payload::<RunJobRequest>()?;
         let job_dao = get_repo_from_context(ctx).await.job();
 
+        if !run_request.sync {
+            // early response to indicate that the job will be run
+            ctx.emit_to(Self::name(), "run_job", ()).await?;
+        }
+
         match run_request.job_type {
             JobType::MigrateContentDescriptors => job_dao.migrate_content_descriptors().await?,
             JobType::CalculateSizes => calculate_all_sizes(ctx).await?,
             JobType::CheckIntegrity => job_dao.check_integrity().await?,
             JobType::Vacuum => job_dao.vacuum().await?,
+            JobType::GenerateThumbnails => job_dao.generate_missing_thumbnails().await?,
         }
 
         Ok(Response::empty())
diff --git a/mediarepo-ui/src-tauri/Cargo.lock b/mediarepo-ui/src-tauri/Cargo.lock
index 1182d6f6..7f087099 100644
--- a/mediarepo-ui/src-tauri/Cargo.lock
+++ b/mediarepo-ui/src-tauri/Cargo.lock
@@ -1500,7 +1500,7 @@ checksum = "a3e378b66a060d48947b590737b30a1be76706c8dd7b8ba0f2fe3989c68a853f"
 
 [[package]]
 name = "mediarepo-api"
-version = "0.29.0"
+version = "0.30.0"
 dependencies = [
  "async-trait",
  "bromine",
diff --git a/mediarepo-ui/src/api/api-types/job.ts b/mediarepo-ui/src/api/api-types/job.ts
index cda973fc..8edff1d3 100644
--- a/mediarepo-ui/src/api/api-types/job.ts
+++ b/mediarepo-ui/src/api/api-types/job.ts
@@ -1,4 +1,5 @@
 export type JobType = "MigrateContentDescriptors"
     | "CalculateSizes"
     | "CheckIntegrity"
-    | "Vacuum";
+    | "Vacuum"
+    | "GenerateThumbnails";
diff --git a/mediarepo-ui/src/api/api-types/requests.ts b/mediarepo-ui/src/api/api-types/requests.ts
index f0bec621..2a813b6e 100644
--- a/mediarepo-ui/src/api/api-types/requests.ts
+++ b/mediarepo-ui/src/api/api-types/requests.ts
@@ -107,6 +107,7 @@ export type SetFrontendStateRequest = {
 
 export type RunJobRequest = {
     jobType: JobType,
+    sync: boolean,
 };
 
 export type AddSortingPresetRequest = {
diff --git a/mediarepo-ui/src/app/components/core/repositories-tab/repositories-tab.component.ts b/mediarepo-ui/src/app/components/core/repositories-tab/repositories-tab.component.ts
index ecb4843b..e045c046 100644
--- a/mediarepo-ui/src/app/components/core/repositories-tab/repositories-tab.component.ts
+++ b/mediarepo-ui/src/app/components/core/repositories-tab/repositories-tab.component.ts
@@ -119,7 +119,9 @@ export class RepositoriesTabComponent implements OnInit, AfterViewInit {
             "Migrating content descriptors to new format...");
         await this.jobService.runJob("MigrateContentDescriptors");
         dialogContext.message.next("Calculating repository sizes...");
-        await this.jobService.runJob("CalculateSizes");
+        await this.jobService.runJob("CalculateSizes", false);
+        dialogContext.message.next("Generating missing thumbnails...");
+        await this.jobService.runJob("GenerateThumbnails");
         dialogContext.message.next("Finished repository startup");
     }
 
diff --git a/mediarepo-ui/src/app/services/file/file.service.ts b/mediarepo-ui/src/app/services/file/file.service.ts
index ab783a92..512f5342 100644
--- a/mediarepo-ui/src/app/services/file/file.service.ts
+++ b/mediarepo-ui/src/app/services/file/file.service.ts
@@ -78,7 +78,7 @@ export class FileService {
      */
     public buildThumbnailUrl(file: File, height: number, width: number): SafeResourceUrl {
         return this.sanitizer.bypassSecurityTrustResourceUrl(
-            `thumb://${file.cd}?width=${250}&height=${250}`);
+            `thumb://${file.cd}?width=${height}&height=${width}`);
     }
 
     /**
diff --git a/mediarepo-ui/src/app/services/job/job.service.ts b/mediarepo-ui/src/app/services/job/job.service.ts
index 404fc08a..44057c36 100644
--- a/mediarepo-ui/src/app/services/job/job.service.ts
+++ b/mediarepo-ui/src/app/services/job/job.service.ts
@@ -10,7 +10,7 @@ export class JobService {
     constructor() {
     }
 
-    public async runJob(jobType: JobType): Promise<void> {
-        return MediarepoApi.runJob({ jobType });
+    public async runJob(jobType: JobType, sync: boolean = true): Promise<void> {
+        return MediarepoApi.runJob({ jobType, sync });
     }
 }