handle ken-burns case with no zoom

src/main/java/jvc/operation/exec/KenBurnsExec.java

@@ -30,11 +30,13 @@ public class KenBurnsExec extends ExecBase<KenBurnsOperation> {
             = "{{{ffmpeg}}} -i {{{source.path}}} -filter_complex \""
             + "scale={{expr width '*' upscale}}x{{expr height '*' upscale}}, "
             + "zoompan="
-            + "z='{{#exists startFrame}}"
-              + "if(between(in,{{startFrame}},{{endFrame}}),min(zoom+{{zoomIncrementFactor}},{{zoom}}),{{zoom}})"
-            + "{{else}}"
-              + "z='min(zoom+{{zoomIncrementFactor}},{{zoom}})':"
-            + "{{/exists}}':"
+            + "{{#if hasZoom}}"
+              + "z='{{#exists startFrame}}"
+                + "if(between(in,{{startFrame}},{{endFrame}}),min(zoom+{{zoomIncrementFactor}},{{zoom}}),{{zoom}})"
+              + "{{else}}"
+                + "z='min(zoom+{{zoomIncrementFactor}},{{zoom}})':"
+              + "{{/exists}}':"
+            + "{{/if}}"
             + "d={{totalFrames}}:"
             + "fps={{fps}}:"
             + "x='if(gte(zoom,{{zoom}}),x,x{{deltaXSign}}{{deltaX}}/a)':"
@@ -75,12 +77,13 @@ public class KenBurnsExec extends ExecBase<KenBurnsOperation> {
 
         final BigDecimal zoom = op.getZoom(ctx, js);
         final BigDecimal totalFrames = duration.multiply(fps);
-        final BigDecimal zoomIncrementFactor = divideBig(zoom.subtract(ONE), totalFrames);
+        final BigDecimal zoomIncrementFactor = zoom.equals(ONE) ? ZERO : divideBig(zoom.subtract(ONE), totalFrames);
 
         ctx.put("zoom", zoom);
         ctx.put("fps", fps.intValue());
         ctx.put("totalFrames", totalFrames.intValue());
         ctx.put("zoomIncrementFactor", zoomIncrementFactor);
+        ctx.put("hasZoom", !zoomIncrementFactor.equals(ZERO));
 
         final BigDecimal midX = divideBig(source.getWidth(), TWO);
         final BigDecimal midY = divideBig(source.getHeight(), TWO);

src/test/resources/tests/test_ken_burns.jvc

@@ -9,6 +9,7 @@
   ],
   "operations": [
     {
+      "comment": "full example - all operation params are specified",
       "operation": "ken-burns",        // name of the operation
       "creates": "ken1",               // asset it creates
       "source": "javelin.jpg",         // source image
@@ -27,6 +28,17 @@
         "comment": "expect output resolution of 1024x768",
         "test": "output.width === 1024 && output.height === 768"
       }]
+    },
+    {
+      "comment": "minimal example - only duration is specified",
+      "operation": "ken-burns",
+      "creates": "ken2",
+      "source": "javelin.jpg",
+      "duration": "5",
+      "validate": [{
+        "comment": "expect output to be about 5 seconds long, give or take 0.1 seconds",
+        "test": "is_within(output.duration, 5, 0.1)"
+      }]
     }
   ]
 }