diff --git a/.idea/dictionaries/bt.xml b/.idea/dictionaries/bt.xml
index 43a605c132..1c5d3c0503 100644
--- a/.idea/dictionaries/bt.xml
+++ b/.idea/dictionaries/bt.xml
@@ -44,6 +44,7 @@
       <w>transcodings</w>
       <w>unpermitted</w>
       <w>upserting</w>
+      <w>upserts</w>
       <w>vits</w>
       <w>vocoded</w>
       <w>vocoder</w>
diff --git a/crates/lib/mysql_queries/src/queries/media_files/mod.rs b/crates/lib/mysql_queries/src/queries/media_files/mod.rs
index 16495dd739..1fa6e3f19b 100644
--- a/crates/lib/mysql_queries/src/queries/media_files/mod.rs
+++ b/crates/lib/mysql_queries/src/queries/media_files/mod.rs
@@ -6,3 +6,4 @@ pub mod get_media_file_for_inference;
 pub mod list;
 pub mod rename_media_file;
 pub mod update_media_file;
+pub mod upsert;
diff --git a/crates/lib/mysql_queries/src/queries/media_files/upsert/mod.rs b/crates/lib/mysql_queries/src/queries/media_files/upsert/mod.rs
new file mode 100644
index 0000000000..089985c1bf
--- /dev/null
+++ b/crates/lib/mysql_queries/src/queries/media_files/upsert/mod.rs
@@ -0,0 +1 @@
+pub mod upsert_media_file_from_file_upload;
\ No newline at end of file
diff --git a/crates/lib/mysql_queries/src/queries/media_files/upsert/upsert_media_file_from_file_upload.rs b/crates/lib/mysql_queries/src/queries/media_files/upsert/upsert_media_file_from_file_upload.rs
new file mode 100644
index 0000000000..0c11c04cc6
--- /dev/null
+++ b/crates/lib/mysql_queries/src/queries/media_files/upsert/upsert_media_file_from_file_upload.rs
@@ -0,0 +1,233 @@
+use anyhow::anyhow;
+use sqlx;
+use sqlx::MySqlPool;
+
+use enums::by_table::generic_synthetic_ids::id_category::IdCategory;
+use enums::by_table::media_files::media_file_class::MediaFileClass;
+use enums::by_table::media_files::media_file_origin_category::MediaFileOriginCategory;
+use enums::by_table::media_files::media_file_origin_product_category::MediaFileOriginProductCategory;
+use enums::by_table::media_files::media_file_subtype::MediaFileSubtype;
+use enums::by_table::media_files::media_file_type::MediaFileType;
+use enums::common::visibility::Visibility;
+use errors::AnyhowResult;
+use tokens::tokens::anonymous_visitor_tracking::AnonymousVisitorTrackingToken;
+use tokens::tokens::media_files::MediaFileToken;
+use tokens::tokens::users::UserToken;
+
+use crate::queries::generic_synthetic_ids::transactional_increment_generic_synthetic_id::transactional_increment_generic_synthetic_id;
+
+pub enum UploadType {
+  Filesystem,
+  DeviceCaptureApi,
+  StorytellerEngine,
+}
+
+pub struct UpsertMediaFileFromUploadArgs<'a> {
+  pub pool: &'a MySqlPool,
+
+  /// If the media file token is present, we're upserting an existing media file.
+  pub maybe_media_file_token: Option<&'a MediaFileToken>,
+
+  pub maybe_creator_user_token: Option<&'a UserToken>,
+  pub maybe_creator_anonymous_visitor_token: Option<&'a AnonymousVisitorTrackingToken>,
+  pub creator_ip_address: &'a str,
+  pub creator_set_visibility: Visibility,
+
+  pub upload_type: UploadType,
+
+  pub media_file_type: MediaFileType,
+  pub maybe_media_class: Option<MediaFileClass>,
+  pub maybe_media_subtype: Option<MediaFileSubtype>,
+
+  pub maybe_mime_type: Option<&'a str>,
+  pub file_size_bytes: u64,
+  pub duration_millis: u64,
+  pub sha256_checksum: &'a str,
+
+  // TODO: Media duration.
+  //pub duration_millis: u64,
+
+  pub public_bucket_directory_hash: &'a str,
+  pub maybe_public_bucket_prefix: Option<&'a str>,
+  pub maybe_public_bucket_extension: Option<&'a str>,
+}
+
+pub async fn upsert_media_file_from_file_upload(
+  args: UpsertMediaFileFromUploadArgs<'_>
+) -> AnyhowResult<(MediaFileToken, u64)>
+{
+  let token = args.maybe_media_file_token
+      .map(|token| token.clone())
+      .unwrap_or_else(|| MediaFileToken::generate());
+
+  let origin_category = match args.upload_type {
+    UploadType::Filesystem => MediaFileOriginCategory::Upload,
+    UploadType::DeviceCaptureApi => MediaFileOriginCategory::DeviceApi,
+    UploadType::StorytellerEngine => MediaFileOriginCategory::StoryEngine,
+  };
+
+  let mut maybe_creator_file_synthetic_id : Option<u64> = None;
+  let mut maybe_creator_category_synthetic_id : Option<u64> = None;
+
+  let mut transaction = args.pool.begin().await?;
+
+  if let Some(user_token) = args.maybe_creator_user_token.as_deref() {
+
+    let next_media_file_id = transactional_increment_generic_synthetic_id(
+      &user_token,
+      IdCategory::MediaFile,
+      &mut transaction
+    ).await?;
+
+    let next_voice_conversion_id = transactional_increment_generic_synthetic_id(
+      &user_token,
+      IdCategory::FileUpload,
+      &mut transaction
+    ).await?;
+
+    maybe_creator_file_synthetic_id = Some(next_media_file_id);
+    maybe_creator_category_synthetic_id = Some(next_voice_conversion_id);
+  }
+
+  const ORIGIN_PRODUCT_CATEGORY : MediaFileOriginProductCategory = MediaFileOriginProductCategory::Unknown;
+
+  let media_class = args.maybe_media_class.unwrap_or(MediaFileClass::Unknown);
+
+  let record_id = {
+    let query_result = sqlx::query!(
+        r#"
+INSERT INTO media_files
+SET
+  token = ?,
+
+  origin_category = ?,
+  origin_product_category = ?,
+
+  maybe_origin_model_type = NULL,
+  maybe_origin_model_token = NULL,
+
+  media_type = ?,
+  media_class = ?,
+  maybe_media_subtype = ?,
+  maybe_mime_type = ?,
+  file_size_bytes = ?,
+
+  checksum_sha2 = ?,
+
+  public_bucket_directory_hash = ?,
+  maybe_public_bucket_prefix = ?,
+  maybe_public_bucket_extension = ?,
+
+  maybe_creator_user_token = ?,
+  maybe_creator_anonymous_visitor_token = ?,
+  creator_ip_address = ?,
+
+  creator_set_visibility = ?,
+
+  maybe_creator_file_synthetic_id = ?,
+  maybe_creator_category_synthetic_id = ?
+
+ON DUPLICATE KEY UPDATE
+
+  origin_category = ?,
+  origin_product_category = ?,
+
+  maybe_origin_model_type = NULL,
+  maybe_origin_model_token = NULL,
+
+  media_type = ?,
+  media_class = ?,
+  maybe_media_subtype = ?,
+  maybe_mime_type = ?,
+  file_size_bytes = ?,
+
+  checksum_sha2 = ?,
+
+  public_bucket_directory_hash = ?,
+  maybe_public_bucket_prefix = ?,
+  maybe_public_bucket_extension = ?,
+
+  maybe_creator_user_token = ?,
+  maybe_creator_anonymous_visitor_token = ?,
+  creator_ip_address = ?,
+
+  creator_set_visibility = ?,
+
+  maybe_creator_file_synthetic_id = ?,
+  maybe_creator_category_synthetic_id = ?
+        "#,
+      token.as_str(),
+
+      origin_category.to_str(),
+      ORIGIN_PRODUCT_CATEGORY.to_str(),
+
+      args.media_file_type.to_str(),
+      media_class.to_str(),
+      args.maybe_media_subtype.map(|s| s.to_str()),
+      
+      args.maybe_mime_type,
+      args.file_size_bytes,
+
+      args.sha256_checksum,
+
+      args.public_bucket_directory_hash,
+      args.maybe_public_bucket_prefix,
+      args.maybe_public_bucket_extension,
+
+      args.maybe_creator_user_token,
+      args.maybe_creator_anonymous_visitor_token,
+      args.creator_ip_address,
+
+      args.creator_set_visibility.to_str(),
+
+      maybe_creator_file_synthetic_id,
+      maybe_creator_category_synthetic_id,
+
+      // Duplicate key
+
+      origin_category.to_str(),
+      ORIGIN_PRODUCT_CATEGORY.to_str(),
+
+      args.media_file_type.to_str(),
+      media_class.to_str(),
+      args.maybe_media_subtype.map(|s| s.to_str()),
+
+      args.maybe_mime_type,
+      args.file_size_bytes,
+
+      args.sha256_checksum,
+
+      args.public_bucket_directory_hash,
+      args.maybe_public_bucket_prefix,
+      args.maybe_public_bucket_extension,
+
+      args.maybe_creator_user_token,
+      args.maybe_creator_anonymous_visitor_token,
+      args.creator_ip_address,
+
+      args.creator_set_visibility.to_str(),
+
+      maybe_creator_file_synthetic_id,
+      maybe_creator_category_synthetic_id,
+    )
+        .execute(&mut *transaction)
+        .await;
+
+    let record_id = match query_result {
+      Ok(res) => {
+        res.last_insert_id()
+      },
+      Err(err) => {
+        // TODO: handle better
+        //transaction.rollback().await?;
+        return Err(anyhow!("Mysql error: {:?}", err));
+      }
+    };
+
+    record_id
+  };
+
+  transaction.commit().await?;
+
+  Ok((token, record_id))
+}
diff --git a/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/mod.rs b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/mod.rs
index 488fce973c..292f240db2 100644
--- a/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/mod.rs
+++ b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/mod.rs
@@ -5,4 +5,5 @@ pub mod get_media_file;
 pub mod list;
 pub mod rename_media_file_handler;
 pub mod update_media_file;
-pub mod upload;
\ No newline at end of file
+pub mod upload;
+pub mod upsert_write;
\ No newline at end of file
diff --git a/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/mod.rs b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/mod.rs
new file mode 100644
index 0000000000..1432d3bf0d
--- /dev/null
+++ b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/mod.rs
@@ -0,0 +1,2 @@
+pub mod write_engine_asset;
+pub mod write_error;
\ No newline at end of file
diff --git a/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_engine_asset/drain_multipart_request.rs b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_engine_asset/drain_multipart_request.rs
new file mode 100644
index 0000000000..872ed9c64e
--- /dev/null
+++ b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_engine_asset/drain_multipart_request.rs
@@ -0,0 +1,106 @@
+use actix_multipart::Multipart;
+use actix_web::web::BytesMut;
+use anyhow::anyhow;
+use futures::TryStreamExt;
+use log::warn;
+use enums::by_table::media_files::media_file_class::MediaFileClass;
+use enums::by_table::media_files::media_file_subtype::MediaFileSubtype;
+
+use errors::AnyhowResult;
+use tokens::tokens::media_files::MediaFileToken;
+use tokens::tokens::zs_voice_datasets::ZsVoiceDatasetToken;
+
+use crate::http_server::web_utils::read_multipart_field_bytes::{checked_read_multipart_bytes, read_multipart_field_as_text};
+
+pub struct MediaFileUploadData {
+  pub uuid_idempotency_token: Option<String>,
+  pub file_name: Option<String>,
+  pub file_bytes: Option<BytesMut>,
+  pub media_file_token: Option<MediaFileToken>,
+  pub media_file_subtype: Option<MediaFileSubtype>,
+  pub media_file_class: Option<MediaFileClass>,
+}
+
+/// Pull common parts out of multipart media HTTP requests, typically for handling file uploads.
+pub async fn drain_multipart_request(mut multipart_payload: Multipart) -> AnyhowResult<MediaFileUploadData> {
+  let mut uuid_idempotency_token = None;
+  let mut file_bytes = None;
+  let mut file_name = None;
+  let mut media_file_token = None;
+  let mut media_file_class = None;
+  let mut media_file_subtype = None;
+
+  while let Ok(Some(mut field)) = multipart_payload.try_next().await {
+    let mut field_name = None;
+    let mut field_filename = None;
+
+    if let content_disposition = field.content_disposition() {
+      field_name = content_disposition.get_name()
+          .map(|s| s.to_string());
+      field_filename = content_disposition.get_filename() // NB: Only used for the file bytes.
+          .map(|s| s.to_string());
+    }
+
+    match field_name.as_deref() {
+      Some("uuid_idempotency_token") => {
+        uuid_idempotency_token = read_multipart_field_as_text(&mut field).await
+            .map_err(|err| {
+              warn!("Error reading idempotency token: {:?}", &err);
+              err
+            })?;
+      },
+      Some("file") => {
+        file_name = field_filename.clone();
+        file_bytes = checked_read_multipart_bytes(&mut field).await
+            .map_err(|err| {
+              warn!("Error reading audio upload: {:?}", &err);
+              err
+            })?;
+      },
+      Some("media_file_token") => {
+        media_file_token = read_multipart_field_as_text(&mut field).await
+            .map_err(|err| {
+              warn!("Error reading source: {:?}", &err);
+              err
+            })?
+            .map(|field| MediaFileToken::new_from_str(&field));
+      },
+      Some("media_file_subtype") => {
+        media_file_subtype = read_multipart_field_as_text(&mut field).await
+            .map_err(|err| {
+              warn!("Error reading source: {:?}", &err);
+              err
+            })?
+            .map(|field| MediaFileSubtype::from_str(&field))
+            .transpose()
+            .map_err(|err| {
+              warn!("Wrong MediaFileSubtype: {:?}", &err);
+              anyhow!("Wrong MediaFileSubtype: {:?}", &err)
+            })?;
+      },
+      Some("media_file_class") => {
+        media_file_class = read_multipart_field_as_text(&mut field).await
+            .map_err(|err| {
+              warn!("Error reading source: {:?}", &err);
+              err
+            })?
+            .map(|field| MediaFileClass::from_str(&field))
+            .transpose()
+            .map_err(|err| {
+              warn!("Wrong MediaFileClass: {:?}", &err);
+              anyhow!("Wrong MediaFileClass: {:?}", &err)
+            })?;
+      },
+      _ => continue,
+    }
+  }
+
+  Ok(MediaFileUploadData {
+    uuid_idempotency_token,
+    file_name,
+    file_bytes,
+    media_file_token,
+    media_file_class,
+    media_file_subtype,
+  })
+}
diff --git a/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_engine_asset/mod.rs b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_engine_asset/mod.rs
new file mode 100644
index 0000000000..02474bf2c5
--- /dev/null
+++ b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_engine_asset/mod.rs
@@ -0,0 +1,2 @@
+pub mod drain_multipart_request;
+pub mod write_engine_asset_media_file_handler;
diff --git a/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_engine_asset/write_engine_asset_media_file_handler.rs b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_engine_asset/write_engine_asset_media_file_handler.rs
new file mode 100644
index 0000000000..272782564d
--- /dev/null
+++ b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_engine_asset/write_engine_asset_media_file_handler.rs
@@ -0,0 +1,239 @@
+use std::collections::HashSet;
+use std::io::{BufReader, Cursor};
+use std::path::PathBuf;
+use std::sync::Arc;
+
+use actix_multipart::Multipart;
+use actix_web::{HttpRequest, HttpResponse, web};
+use log::{error, info, warn};
+use once_cell::sync::Lazy;
+use utoipa::ToSchema;
+
+use buckets::public::media_files::bucket_file_path::MediaFileBucketPath;
+use enums::by_table::media_files::media_file_type::MediaFileType;
+use enums::common::visibility::Visibility;
+use hashing::sha256::sha256_hash_bytes::sha256_hash_bytes;
+use http_server_common::request::get_request_ip::get_request_ip;
+use mimetypes::mimetype_for_bytes::get_mimetype_for_bytes;
+use mimetypes::mimetype_to_extension::mimetype_to_extension;
+use mysql_queries::queries::idepotency_tokens::insert_idempotency_token::insert_idempotency_token;
+use mysql_queries::queries::media_files::upsert::upsert_media_file_from_file_upload::{upsert_media_file_from_file_upload, UpsertMediaFileFromUploadArgs, UploadType};
+use tokens::tokens::media_files::MediaFileToken;
+use videos::get_mp4_info::{get_mp4_info, get_mp4_info_for_bytes, get_mp4_info_for_bytes_and_len};
+
+use crate::http_server::endpoints::media_files::upsert_write::write_engine_asset::drain_multipart_request::drain_multipart_request;
+use crate::http_server::endpoints::media_files::upsert_write::write_error::MediaFileWriteError;
+use crate::server_state::ServerState;
+use crate::validations::validate_idempotency_token_format::validate_idempotency_token_format;
+
+// Unlike the "upload" endpoints, which are pure inserts, these endpoints are *upserts*.
+#[derive(Serialize, ToSchema)]
+pub struct WriteEngineAssetMediaSuccessResponse {
+  pub success: bool,
+  pub media_file_token: MediaFileToken,
+}
+
+#[utoipa::path(
+  post,
+  path = "/v1/media_files/write/engine_asset",
+  responses(
+    (status = 200, description = "Success Update", body = WriteEngineAssetMediaSuccessResponse),
+    (status = 400, description = "Bad input", body = MediaFileWriteError),
+    (status = 401, description = "Not authorized", body = MediaFileWriteError),
+    (status = 429, description = "Too many requests", body = MediaFileWriteError),
+    (status = 500, description = "Server error", body = MediaFileWriteError),
+  ),
+  params(
+    ("request" = (), description = "Ask Brandon. This is form-multipart."),
+  )
+)]
+pub async fn write_engine_asset_media_file_handler(
+  http_request: HttpRequest,
+  server_state: web::Data<Arc<ServerState>>,
+  mut multipart_payload: Multipart,
+) -> Result<HttpResponse, MediaFileWriteError> {
+
+  let mut mysql_connection = server_state.mysql_pool
+      .acquire()
+      .await
+      .map_err(|err| {
+        error!("MySql pool error: {:?}", err);
+        MediaFileWriteError::ServerError
+      })?;
+
+  // ==================== READ SESSION ==================== //
+
+  let maybe_user_session = server_state
+      .session_checker
+      .maybe_get_user_session_from_connection(&http_request, &mut mysql_connection)
+      .await
+      .map_err(|e| {
+        error!("Session checker error: {:?}", e);
+        MediaFileWriteError::ServerError
+      })?;
+
+  let maybe_avt_token = server_state
+      .avt_cookie_manager
+      .get_avt_token_from_request(&http_request);
+
+  // ==================== BANNED USERS ==================== //
+
+  if let Some(ref user) = maybe_user_session {
+    if user.is_banned {
+      return Err(MediaFileWriteError::NotAuthorized);
+    }
+  }
+
+  // ==================== RATE LIMIT ==================== //
+
+  let rate_limiter = match maybe_user_session {
+    None => &server_state.redis_rate_limiters.file_upload_logged_out,
+    Some(ref _session) => &server_state.redis_rate_limiters.file_upload_logged_in,
+  };
+
+  if let Err(_err) = rate_limiter.rate_limit_request(&http_request) {
+    return Err(MediaFileWriteError::RateLimited);
+  }
+
+  // ==================== READ MULTIPART REQUEST ==================== //
+
+  let upload_media_request = drain_multipart_request(multipart_payload)
+      .await
+      .map_err(|e| {
+        // TODO: Error handling could be nicer.
+        MediaFileWriteError::BadInput("bad request".to_string())
+      })?;
+
+  // TODO(bt, 2024-02-26): This should be a transaction.
+  let uuid_idempotency_token = upload_media_request.uuid_idempotency_token
+      .ok_or(MediaFileWriteError::BadInput("no uuid".to_string()))?;
+
+  // ==================== HANDLE IDEMPOTENCY ==================== //
+
+  if let Err(reason) = validate_idempotency_token_format(&uuid_idempotency_token) {
+    return Err(MediaFileWriteError::BadInput(reason));
+  }
+
+  insert_idempotency_token(&uuid_idempotency_token, &mut *mysql_connection)
+      .await
+      .map_err(|err| {
+        error!("Error inserting idempotency token: {:?}", err);
+        MediaFileWriteError::BadInput("invalid idempotency token".to_string())
+      })?;
+
+  // ==================== UPLOAD METADATA ==================== //
+
+  let creator_set_visibility = maybe_user_session
+      .as_ref()
+      .map(|user_session| user_session.preferred_tts_result_visibility) // TODO: We need a new type of visibility control.
+      .unwrap_or(Visibility::default());
+
+  // ==================== USER DATA ==================== //
+
+  let ip_address = get_request_ip(&http_request);
+
+  let maybe_user_token = maybe_user_session
+      .map(|session| session.get_strongly_typed_user_token());
+
+  // ==================== FILE DATA ==================== //
+
+  let file_bytes = match upload_media_request.file_bytes {
+    None => return Err(MediaFileWriteError::BadInput("missing file contents".to_string())),
+    Some(bytes) => bytes,
+  };
+
+  let maybe_filename = upload_media_request.file_name
+      .as_deref()
+      .map(|filename| PathBuf::from(filename));
+
+  let maybe_file_extension = maybe_filename
+      .as_ref()
+      .and_then(|filename| filename.extension())
+      .and_then(|ext| ext.to_str());
+
+  let (suffix, media_file_type, mimetype) = match maybe_file_extension {
+    None => {
+      return Err(MediaFileWriteError::BadInput("no file extension".to_string()));
+    }
+    Some("bvh") => (".bvh", MediaFileType::Bvh, "application/octet-stream"),
+    Some("fbx") => (".fbx", MediaFileType::Fbx, "application/octet-stream"),
+    Some("glb") => (".glb", MediaFileType::Glb, "application/octet-stream"),
+    Some("gltf") => (".gltf", MediaFileType::Gltf, "application/octet-stream"),
+    Some("ron") => (".scn.ron", MediaFileType::SceneRon, "application/octet-stream"),
+    _ => {
+      return Err(MediaFileWriteError::BadInput(
+        "unsupported file extension. Must be bvh, glb, gltf, or fbx.".to_string()));
+    }
+  };
+
+  let file_size_bytes = file_bytes.len();
+
+  let hash = sha256_hash_bytes(&file_bytes)
+      .map_err(|io_error| {
+        error!("Problem hashing bytes: {:?}", io_error);
+        MediaFileWriteError::ServerError
+      })?;
+
+  // ==================== UPLOAD AND SAVE ==================== //
+
+  // TODO(bt,2024-03-26): At first I thought we should map these to the existing file paths on upsert,
+  //  but now I'm thinking we can just lead cruft in the bucket and clean it later. We don't have the
+  //  benefit of restoring old versions (if we mapped to existing paths but had a versioning scheme),
+  //  but we can move fast.
+
+  const PREFIX : Option<&str> = Some("upload_");
+
+  let public_upload_path = MediaFileBucketPath::generate_new(PREFIX, Some(suffix));
+
+  info!("Uploading media to bucket path: {}", public_upload_path.get_full_object_path_str());
+
+  server_state.public_bucket_client.upload_file_with_content_type(
+    public_upload_path.get_full_object_path_str(),
+    file_bytes.as_ref(),
+    mimetype)
+      .await
+      .map_err(|e| {
+        warn!("Upload media bytes to bucket error: {:?}", e);
+        MediaFileWriteError::ServerError
+      })?;
+
+  // TODO(bt, 2024-02-22): This should be a transaction.
+  let (token, record_id) = upsert_media_file_from_file_upload(UpsertMediaFileFromUploadArgs {
+    maybe_media_file_token: upload_media_request.media_file_token.as_ref(),
+    maybe_creator_user_token: maybe_user_token.as_ref(),
+    maybe_creator_anonymous_visitor_token: maybe_avt_token.as_ref(),
+    creator_ip_address: &ip_address,
+    creator_set_visibility,
+    upload_type: UploadType::Filesystem,
+    media_file_type,
+    maybe_media_class: upload_media_request.media_file_class,
+    maybe_media_subtype: upload_media_request.media_file_subtype,
+    maybe_mime_type: Some(mimetype),
+    file_size_bytes: file_size_bytes as u64,
+    duration_millis: 0,
+    sha256_checksum: &hash,
+    public_bucket_directory_hash: public_upload_path.get_object_hash(),
+    maybe_public_bucket_prefix: PREFIX,
+    maybe_public_bucket_extension: Some(suffix),
+    pool: &server_state.mysql_pool,
+  })
+      .await
+      .map_err(|err| {
+        warn!("New file creation DB error: {:?}", err);
+        MediaFileWriteError::ServerError
+      })?;
+
+  info!("new media file id: {} token: {:?}", record_id, &token);
+
+  let response = WriteEngineAssetMediaSuccessResponse {
+    success: true,
+    media_file_token: token,
+  };
+
+  let body = serde_json::to_string(&response)
+      .map_err(|e| MediaFileWriteError::ServerError)?;
+
+  return Ok(HttpResponse::Ok()
+      .content_type("application/json")
+      .body(body));
+}
diff --git a/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_error.rs b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_error.rs
new file mode 100644
index 0000000000..fd47feaaf2
--- /dev/null
+++ b/crates/service/web/storyteller_web/src/http_server/endpoints/media_files/upsert_write/write_error.rs
@@ -0,0 +1,37 @@
+use actix_web::error::ResponseError;
+use actix_web::http::StatusCode;
+use actix_web::HttpResponse;
+use utoipa::ToSchema;
+
+use http_server_common::response::serialize_as_json_error::serialize_as_json_error;
+
+#[derive(Debug, Serialize, ToSchema)]
+pub enum MediaFileWriteError {
+  BadInput(String),
+  NotAuthorized,
+  MustBeLoggedIn,
+  ServerError,
+  RateLimited,
+}
+
+impl ResponseError for MediaFileWriteError {
+  fn status_code(&self) -> StatusCode {
+    match *self {
+      MediaFileWriteError::BadInput(_) => StatusCode::BAD_REQUEST,
+      MediaFileWriteError::NotAuthorized => StatusCode::UNAUTHORIZED,
+      MediaFileWriteError::MustBeLoggedIn => StatusCode::UNAUTHORIZED,
+      MediaFileWriteError::ServerError => StatusCode::INTERNAL_SERVER_ERROR,
+      MediaFileWriteError::RateLimited => StatusCode::TOO_MANY_REQUESTS,
+    }
+  }
+
+  fn error_response(&self) -> HttpResponse {
+    serialize_as_json_error(self)
+  }
+}
+
+impl std::fmt::Display for MediaFileWriteError {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    write!(f, "{:?}", self)
+  }
+}
diff --git a/crates/service/web/storyteller_web/src/routes/media_files_routes.rs b/crates/service/web/storyteller_web/src/routes/media_files_routes.rs
index d3c17e3251..4a62a51f52 100644
--- a/crates/service/web/storyteller_web/src/routes/media_files_routes.rs
+++ b/crates/service/web/storyteller_web/src/routes/media_files_routes.rs
@@ -16,6 +16,7 @@ use crate::http_server::endpoints::media_files::update_media_file::update_media_
 use crate::http_server::endpoints::media_files::upload::upload_generic::upload_media_file_handler::upload_media_file_handler;
 use crate::http_server::endpoints::media_files::upload::upload_engine_asset::upload_engine_asset_media_file_handler::upload_engine_asset_media_file_handler;
 use crate::http_server::endpoints::media_files::upload::upload_video::upload_video_media_file_handler::upload_video_media_file_handler;
+use crate::http_server::endpoints::media_files::upsert_write::write_engine_asset::write_engine_asset_media_file_handler::write_engine_asset_media_file_handler;
 
 pub fn add_media_file_routes<T, B> (app: App<T>) -> App<T>
   where
@@ -75,13 +76,13 @@ pub fn add_media_file_routes<T, B> (app: App<T>) -> App<T>
           .route(web::post().to(upload_engine_asset_media_file_handler))
           .route(web::head().to(|| HttpResponse::Ok()))
       )
-//      .service(web::resource("/write/engine_asset")
-//          .route(web::post().to(/* todo */))
-//          .route(web::head().to(|| HttpResponse::Ok()))
-//      )
-//      .service(web::resource("/write/scene_file")
-//          .route(web::post().to(/* todo */))
-//          .route(web::head().to(|| HttpResponse::Ok()))
-//      )
+      .service(web::resource("/write/engine_asset")
+          .route(web::post().to(write_engine_asset_media_file_handler))
+          .route(web::head().to(|| HttpResponse::Ok()))
+      )
+      //.service(web::resource("/write/scene_file")
+      //    .route(web::post().to(/* todo */))
+      //    .route(web::head().to(|| HttpResponse::Ok()))
+      //)
   )
 }