When serializing md5+ext, the name should reflect that. Deserializing translates this name back to what vm and other components currently expect.

src/serialization/sb2.js

@@ -224,9 +224,16 @@ const parseScratchObject = function (object, runtime, extensions, topLevel) {
                 bitmapResolution: costumeSource.bitmapResolution || 1,
                 rotationCenterX: costumeSource.rotationCenterX,
                 rotationCenterY: costumeSource.rotationCenterY,
+                // TODO we eventually want this next property to be called
+                // md5ext to reflect what it actually contains, however this
+                // will be a very extensive change across many repositories
+                // and should be done carefully and altogether
+                md5: costumeSource.baseLayerMD5,
                 skinId: null
             };
-            costumePromises.push(loadCostume(costumeSource.baseLayerMD5, costume, runtime));
+            // TODO need to add deserializeCostume here so that assets from
+            // actual .sb2s get loaded in
+            costumePromises.push(loadCostume(costume.md5, costume, runtime));
         }
     }
     // Sounds from JSON
@@ -240,9 +247,17 @@ const parseScratchObject = function (object, runtime, extensions, topLevel) {
                 rate: soundSource.rate,
                 sampleCount: soundSource.sampleCount,
                 soundID: soundSource.soundID,
+                // TODO we eventually want this next property to be called
+                // md5ext to reflect what it actually contains, however this
+                // will be a very extensive change across many repositories
+                // and should be done carefully and altogether
+                // (for example, the audio engine currently relies on this
+                // property to be named 'md5')
                 md5: soundSource.md5,
                 data: null
             };
+            // TODO need to add deserializeSound here so that assets from
+            // actual .sb2s get loaded in
             soundPromises.push(loadSound(sound, runtime));
         }
     }

src/serialization/sb3.js

@@ -62,6 +62,12 @@ const serializeCostume = function (costume) {
     obj.assetId = costume.assetId;
     obj.name = costume.name;
     obj.bitmapResolution = costume.bitmapResolution;
+    // serialize this property with the name 'md5ext' because that's
+    // what it's actually referring to. TODO runtime objects need to be
+    // updated to actually refer to this as 'md5ext' instead of 'md5'
+    // but that change should be made carefully since it is very
+    // pervasive
+    obj.md5ext = costume.md5;
     obj.dataFormat = costume.dataFormat;
     obj.rotationCenterX = costume.rotationCenterX;
     obj.rotationCenterY = costume.rotationCenterY;
@@ -76,8 +82,12 @@ const serializeSound = function (sound) {
     obj.format = sound.format;
     obj.rate = sound.rate;
     obj.sampleCount = sound.sampleCount;
-    // TODO eventually want to get rid of this
+    // serialize this property with the name 'md5ext' because that's
-    obj.md5 = sound.md5;
+    // what it's actually referring to. TODO runtime objects need to be
+    // updated to actually refer to this as 'md5ext' instead of 'md5'
+    // but that change should be made carefully since it is very
+    // pervasive
+    obj.md5ext = sound.md5;
     // TODO do we need this soundID
     // (not to be confused with soundId which is a uid for sounds)
     // obj.soundID = sound.soundID;
@@ -176,6 +186,7 @@ const parseScratchObject = function (object, runtime, extensions, zip) {
     const costumePromises = (object.costumes || []).map(costumeSource => {
         // @todo: Make sure all the relevant metadata is being pulled out.
         const costume = {
+            assetId: costumeSource.assetId,
             skinId: null,
             name: costumeSource.name,
             bitmapResolution: costumeSource.bitmapResolution,
@@ -186,24 +197,41 @@ const parseScratchObject = function (object, runtime, extensions, zip) {
             costumeSource.dataFormat ||
             (costumeSource.assetType && costumeSource.assetType.runtimeFormat) || // older format
             'png'; // if all else fails, guess that it might be a PNG
-        const costumeMd5 = `${costumeSource.assetId}.${dataFormat}`;
+        const costumeMd5Ext = costumeSource.hasOwnProperty('md5ext') ?
-        costume.md5 = costumeMd5;
+            costumeSource.md5ext : `${costumeSource.assetId}.${dataFormat}`;
-        return deserializeCostume(costumeSource, runtime, zip)
+        costume.md5 = costumeMd5Ext;
-            .then(() => loadCostume(costumeMd5, costume, runtime));
+        costume.dataFormat = dataFormat;
+        // deserializeCostume should be called on the costume object we're
+        // creating above instead of the source costume object, because this way
+        // we're always loading the 'sb3' representation of the costume
+        // any translation that needs to happen will happen in the process
+        // of building up the costume object into an sb3 format
+        return deserializeCostume(costume, runtime, zip)
+            .then(() => loadCostume(costumeMd5Ext, costume, runtime));
         // Only attempt to load the costume after the deserialization
         // process has been completed
     });
     // Sounds from JSON
     const soundPromises = (object.sounds || []).map(soundSource => {
         const sound = {
+            assetId: soundSource.assetId,
             format: soundSource.format,
             rate: soundSource.rate,
             sampleCount: soundSource.sampleCount,
             name: soundSource.name,
-            md5: soundSource.md5,
+            // TODO we eventually want this property to be called md5ext,
+            // but there are many things relying on this particular name at the
+            // moment, so this translation is very important
+            md5: soundSource.md5ext,
+            dataFormat: soundSource.dataFormat,
             data: null
         };
-        return deserializeSound(soundSource, runtime, zip)
+        // deserializeSound should be called on the sound object we're
+        // creating above instead of the source sound object, because this way
+        // we're always loading the 'sb3' representation of the costume
+        // any translation that needs to happen will happen in the process
+        // of building up the costume object into an sb3 format
+        return deserializeSound(sound, runtime, zip)
             .then(() => loadSound(sound, runtime));
         // Only attempt to load the sound after the deserialization
         // process has been completed.

src/serialization/serialize-assets.js

@@ -19,8 +19,7 @@ const serializeAssets = function (runtime, assetType) {
             const storage = runtime.storage;
             const storedAsset = storage.get(assetId);
             assetDescs.push({
-                fileName: currAsset.md5 ?
+                fileName: `${assetId}.${storedAsset.dataFormat}`,
-                    currAsset.md5 : `${assetId}.${storedAsset.dataFormat}`,
                 fileContent: storedAsset.data});
         }
     }