Use log filename as suggested video export filename

app/js/flightlog_video_renderer.js

@@ -276,14 +276,22 @@ function FlightLogVideoRenderer(flightLog, logParameters, videoOptions) {
             prepareRender = Promise.resolve();
         }
 
-	    prepareRender
-            .then(function() {
-	            renderChunk();
-            })
-            .catch(function(error) {
-                console.error(error);
-                notifyCompletion(false);
-            });
+        /* Ensure caller can have a chance to update the DOM before we start trying to render (so they can throw up
+         * a "video rendering..." message)
+         */
+        setTimeout(
+            function() {
+                prepareRender
+		            .then(function() {
+			            renderChunk();
+		            })
+		            .catch(function(error) {
+			            console.error(error);
+			            notifyCompletion(false);
+		            })
+            },
+            0
+        );
     };
 
     /**

app/js/main.js

@@ -5,7 +5,7 @@ const
 
 	fs = require('fs'),
 
-    {formatTime} = require("./misc.js"),
+    {formatTime, setFileExtension} = require("./misc.js"),
 	FlightLogVideoRenderer = require("./flightlog_video_renderer.js"),
     FlightLogFieldPresenter = require("./flightlog_fields_presenter.js"),
     VideoExportDialog = require("./video_export_dialog.js"),
@@ -67,6 +67,8 @@ function BlackboxLogViewer() {
         graphLegend = null,
         fieldPresenter = FlightLogFieldPresenter,
 
+        logFilename = null,
+
         hasVideo = false, hasLog = false,
         video = $(".log-graph video")[0],
         canvas = $("#graphCanvas")[0],
@@ -501,6 +503,7 @@ function BlackboxLogViewer() {
                 return;
             }
 
+            logFilename = file.path;
             renderLogFileInfo(file);
 
             hasLog = true;
@@ -582,30 +585,35 @@ function BlackboxLogViewer() {
 	    prefs.set('videoConfig', videoConfig);
 
         if (videoConfig.format == "webm") {
-	        pickFilename = pickOutputFile("video.webm", {
+	        pickFilename = pickOutputFile(setFileExtension(logFilename, ".webm"), {
 		        name: "WebM video",
 		        extensions: ["webm"]
 	        });
         } else {
-	        pickFilename = pickOutputFile("video.png", {
+	        pickFilename = pickOutputFile(setFileExtension(logFilename, ".png"), {
 		        name: "PNG frames",
 		        extensions: ["png"]
 	        });
         }
 
 	    pickFilename
+            .catch(function() {
+                videoExportDialog.close();
+
+                return Promise.reject();
+            })
             .then(function(filename) {
                 videoConfig.filename = filename;
             })
             .then(function() {
                 var
                     videoRenderer = new FlightLogVideoRenderer(flightLog, logParameters, videoConfig);
-            
-                videoRenderer.start();
-            
-                videoExportDialog.onRenderingBegin(videoRenderer);
+	
+	            videoRenderer.start();
+	
+	            videoExportDialog.onRenderingBegin(videoRenderer);
 
-                videoExportDialog.once("cancel", function() {
+	            videoExportDialog.once("cancel", function() {
                     videoRenderer.cancel();
                 });
             });

app/js/misc.js

@@ -1,3 +1,6 @@
+const
+	path = require("path");
+
 function leftPad(string, pad, minLength) {
 	// Coerce value to string:
 	string = "" + string;
@@ -28,4 +31,28 @@ function formatTime(msec, displayMsec) {
 		+ (displayMsec ? "." + leftPad(msec, "0", 3) : "");
 }
 
-module.exports = {leftPad, formatTime};
+/**
+ * Change the extension of the given filename.
+ *
+ * @param {String} filename - A valid path and filename
+ * @param {String} extension - Should include the dot, e.g. ".jpg"
+ * @returns {string}
+ */
+function setFileExtension(filename, extension) {
+	var
+		directory = path.dirname(filename),
+		name = path.basename(filename);
+
+	if (name.length == 0) {
+		throw new Error("Empty filename not allowed");
+	}
+
+	// Remove existing file extension if present
+	if (name.lastIndexOf(".") > -1) {
+		name = name.substring(0, name.lastIndexOf("."));
+	}
+
+	return path.join(directory, name + extension);
+}
+
+module.exports = {leftPad, formatTime, setFileExtension};

app/js/video_export_dialog.js

@@ -160,7 +160,18 @@ function VideoExportDialog(dialog) {
         populateConfig(videoConfig);
     };
 
+    this.close = function() {
+		dialog.modal("hide");
+    };
+
     this.onRenderingBegin = function(videoRenderer) {
+	    progressBar.prop('value', 0);
+	    progressRenderedFrames.text('');
+	    progressRemaining.text('');
+	    progressSize.text('Calculating...');
+
+	    setDialogMode(DIALOG_MODE_IN_PROGRESS);
+
 	    renderStartTime = Date.now();
 	    lastEstimatedTimeMsec = false;
 
@@ -173,7 +184,7 @@ function VideoExportDialog(dialog) {
 			    $(".video-export-result").text("Rendered " + frameCount + " frames in " + formatTime(Date.now() - renderStartTime, false));
 			    setDialogMode(DIALOG_MODE_COMPLETE);
 		    } else {
-			    dialog.modal('hide');
+			    that.close();
 		    }
 	    });
     };
@@ -182,13 +193,6 @@ function VideoExportDialog(dialog) {
 	    e.preventDefault();
 
 	    that.emit("optionsChosen", that.logParameters, convertUIToVideoConfig());
-
-	    progressBar.prop('value', 0);
-	    progressRenderedFrames.text('');
-	    progressRemaining.text('');
-	    progressSize.text('Calculating...');
-
-	    setDialogMode(DIALOG_MODE_IN_PROGRESS);
     });
 
     $(".video-export-dialog-cancel").click(function(e) {