diff --git a/Jellyfin.Api/Controllers/ImageController.cs b/Jellyfin.Api/Controllers/ImageController.cs
index 3c5f18af5..7b10ea170 100644
--- a/Jellyfin.Api/Controllers/ImageController.cs
+++ b/Jellyfin.Api/Controllers/ImageController.cs
@@ -7,6 +7,7 @@ using System.Globalization;
 using System.IO;
 using System.Linq;
 using System.Net.Mime;
+using System.Security.Cryptography;
 using System.Threading;
 using System.Threading.Tasks;
 using Jellyfin.Api.Attributes;
@@ -78,6 +79,9 @@ public class ImageController : BaseJellyfinApiController
         _appPaths = appPaths;
     }
 
+    private static Stream GetFromBase64Stream(Stream inputStream)
+        => new CryptoStream(inputStream, new FromBase64Transform(), CryptoStreamMode.Read);
+
     /// <summary>
     /// Sets the user image.
     /// </summary>
@@ -116,8 +120,8 @@ public class ImageController : BaseJellyfinApiController
             return BadRequest("Incorrect ContentType.");
         }
 
-        var memoryStream = await GetMemoryStream(Request.Body).ConfigureAwait(false);
-        await using (memoryStream.ConfigureAwait(false))
+        var stream = GetFromBase64Stream(Request.Body);
+        await using (stream.ConfigureAwait(false))
         {
             // Handle image/png; charset=utf-8
             var mimeType = Request.ContentType?.Split(';').FirstOrDefault();
@@ -130,7 +134,7 @@ public class ImageController : BaseJellyfinApiController
             user.ProfileImage = new Data.Entities.ImageInfo(Path.Combine(userDataPath, "profile" + extension));
 
             await _providerManager
-                .SaveImage(memoryStream, mimeType, user.ProfileImage.Path)
+                .SaveImage(stream, mimeType, user.ProfileImage.Path)
                 .ConfigureAwait(false);
             await _userManager.UpdateUserAsync(user).ConfigureAwait(false);
 
@@ -176,8 +180,8 @@ public class ImageController : BaseJellyfinApiController
             return BadRequest("Incorrect ContentType.");
         }
 
-        var memoryStream = await GetMemoryStream(Request.Body).ConfigureAwait(false);
-        await using (memoryStream.ConfigureAwait(false))
+        var stream = GetFromBase64Stream(Request.Body);
+        await using (stream.ConfigureAwait(false))
         {
             // Handle image/png; charset=utf-8
             var mimeType = Request.ContentType?.Split(';').FirstOrDefault();
@@ -190,7 +194,7 @@ public class ImageController : BaseJellyfinApiController
             user.ProfileImage = new Data.Entities.ImageInfo(Path.Combine(userDataPath, "profile" + extension));
 
             await _providerManager
-                .SaveImage(memoryStream, mimeType, user.ProfileImage.Path)
+                .SaveImage(stream, mimeType, user.ProfileImage.Path)
                 .ConfigureAwait(false);
             await _userManager.UpdateUserAsync(user).ConfigureAwait(false);
 
@@ -372,12 +376,12 @@ public class ImageController : BaseJellyfinApiController
             return BadRequest("Incorrect ContentType.");
         }
 
-        var memoryStream = await GetMemoryStream(Request.Body).ConfigureAwait(false);
-        await using (memoryStream.ConfigureAwait(false))
+        var stream = GetFromBase64Stream(Request.Body);
+        await using (stream.ConfigureAwait(false))
         {
             // Handle image/png; charset=utf-8
             var mimeType = Request.ContentType?.Split(';').FirstOrDefault();
-            await _providerManager.SaveImage(item, memoryStream, mimeType, imageType, null, CancellationToken.None).ConfigureAwait(false);
+            await _providerManager.SaveImage(item, stream, mimeType, imageType, null, CancellationToken.None).ConfigureAwait(false);
             await item.UpdateToRepositoryAsync(ItemUpdateType.ImageUpdate, CancellationToken.None).ConfigureAwait(false);
 
             return NoContent();
@@ -416,12 +420,12 @@ public class ImageController : BaseJellyfinApiController
             return BadRequest("Incorrect ContentType.");
         }
 
-        var memoryStream = await GetMemoryStream(Request.Body).ConfigureAwait(false);
-        await using (memoryStream.ConfigureAwait(false))
+        var stream = GetFromBase64Stream(Request.Body);
+        await using (stream.ConfigureAwait(false))
         {
             // Handle image/png; charset=utf-8
             var mimeType = Request.ContentType?.Split(';').FirstOrDefault();
-            await _providerManager.SaveImage(item, memoryStream, mimeType, imageType, null, CancellationToken.None).ConfigureAwait(false);
+            await _providerManager.SaveImage(item, stream, mimeType, imageType, null, CancellationToken.None).ConfigureAwait(false);
             await item.UpdateToRepositoryAsync(ItemUpdateType.ImageUpdate, CancellationToken.None).ConfigureAwait(false);
 
             return NoContent();
@@ -1792,8 +1796,8 @@ public class ImageController : BaseJellyfinApiController
             return BadRequest("Incorrect ContentType.");
         }
 
-        var memoryStream = await GetMemoryStream(Request.Body).ConfigureAwait(false);
-        await using (memoryStream.ConfigureAwait(false))
+        var stream = GetFromBase64Stream(Request.Body);
+        await using (stream.ConfigureAwait(false))
         {
             var filePath = Path.Combine(_appPaths.DataPath, "splashscreen-upload" + extension);
             var brandingOptions = _serverConfigurationManager.GetConfiguration<BrandingOptions>("branding");
@@ -1803,7 +1807,7 @@ public class ImageController : BaseJellyfinApiController
             var fs = new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.None, IODefaults.FileStreamBufferSize, FileOptions.Asynchronous);
             await using (fs.ConfigureAwait(false))
             {
-                await memoryStream.CopyToAsync(fs, CancellationToken.None).ConfigureAwait(false);
+                await stream.CopyToAsync(fs, CancellationToken.None).ConfigureAwait(false);
             }
 
             return NoContent();
@@ -1833,15 +1837,6 @@ public class ImageController : BaseJellyfinApiController
         return NoContent();
     }
 
-    private static async Task<MemoryStream> GetMemoryStream(Stream inputStream)
-    {
-        using var reader = new StreamReader(inputStream);
-        var text = await reader.ReadToEndAsync().ConfigureAwait(false);
-
-        var bytes = Convert.FromBase64String(text);
-        return new MemoryStream(bytes, 0, bytes.Length, false, true);
-    }
-
     private ImageInfo? GetImageInfo(BaseItem item, ItemImageInfo info, int? imageIndex)
     {
         int? width = null;
diff --git a/Jellyfin.Api/Controllers/SubtitleController.cs b/Jellyfin.Api/Controllers/SubtitleController.cs
index 7d02550b6..fb89e9610 100644
--- a/Jellyfin.Api/Controllers/SubtitleController.cs
+++ b/Jellyfin.Api/Controllers/SubtitleController.cs
@@ -6,6 +6,7 @@ using System.Globalization;
 using System.IO;
 using System.Linq;
 using System.Net.Mime;
+using System.Security.Cryptography;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -405,9 +406,8 @@ public class SubtitleController : BaseJellyfinApiController
         [FromBody, Required] UploadSubtitleDto body)
     {
         var video = (Video)_libraryManager.GetItemById(itemId);
-        var data = Convert.FromBase64String(body.Data);
-        var memoryStream = new MemoryStream(data, 0, data.Length, false, true);
-        await using (memoryStream.ConfigureAwait(false))
+        var stream = new CryptoStream(Request.Body, new FromBase64Transform(), CryptoStreamMode.Read);
+        await using (stream.ConfigureAwait(false))
         {
             await _subtitleManager.UploadSubtitle(
                 video,
@@ -417,7 +417,7 @@ public class SubtitleController : BaseJellyfinApiController
                     Language = body.Language,
                     IsForced = body.IsForced,
                     IsHearingImpaired = body.IsHearingImpaired,
-                    Stream = memoryStream
+                    Stream = stream
                 }).ConfigureAwait(false);
             _providerManager.QueueRefresh(video.Id, new MetadataRefreshOptions(new DirectoryService(_fileSystem)), RefreshPriority.High);
 
diff --git a/MediaBrowser.Providers/Manager/ImageSaver.cs b/MediaBrowser.Providers/Manager/ImageSaver.cs
index e7c2cd255..d82716831 100644
--- a/MediaBrowser.Providers/Manager/ImageSaver.cs
+++ b/MediaBrowser.Providers/Manager/ImageSaver.cs
@@ -263,7 +263,11 @@ namespace MediaBrowser.Providers.Manager
 
                 var fileStreamOptions = AsyncFile.WriteOptions;
                 fileStreamOptions.Mode = FileMode.Create;
-                fileStreamOptions.PreallocationSize = source.Length;
+                if (source.CanSeek)
+                {
+                    fileStreamOptions.PreallocationSize = source.Length;
+                }
+
                 var fs = new FileStream(path, fileStreamOptions);
                 await using (fs.ConfigureAwait(false))
                 {