src/: fail --load-tape-create-video if video encoding fails.

Also fail video encoding if output file already exists.

src/Aircraft/replay-internal.cxx

@@ -1783,13 +1783,15 @@ bool loadTapeContinuous(
     {
         continuous->m_replay_fixed_dt_prev = -1;
     }
-    if (continuous->m_replay_create_video)
+    
+    bool ok = true;
+    if (ok && continuous->m_replay_create_video)
     {
         SG_LOG(SG_GENERAL, SG_ALERT, "Replaying with create-video");
         auto view_mgr = globals->get_subsystem<FGViewMgr>();
         if (view_mgr)
         {
-            view_mgr->video_start(
+            ok = view_mgr->video_start(
                     "" /*name*/,
                     "" /*codec*/,
                     -1 /*quality*/,
@@ -1797,9 +1799,14 @@ bool loadTapeContinuous(
                     0 /*bitrate*/
                     );
         }
+        else
+        {
+            SG_LOG(SG_GENERAL, SG_ALERT, "Cannot handle create_video=true because FGViewMgr not available");
+            ok = false;
         }
-    replay_internal.start(true /*new_tape*/);
+    }
-    return true;
+    if (ok) ok = replay_internal.start(true /*new_tape*/);
+    return ok;
 }
 
 /** Read a flight recorder tape with given filename from disk.

src/Viewer/viewmgr.cxx

@@ -366,7 +366,7 @@ FGViewMgr::add_view( flightgear::View * v )
   v->init();
 }
 
-void FGViewMgr::video_start(
+bool FGViewMgr::video_start(
         const std::string& name_in,
         const std::string& codec_in,
         double quality,
@@ -413,6 +413,11 @@ void FGViewMgr::video_start(
     SGPath  path = SGPath(fgGetString("/sim/video/directory"));
     SGPath  path_link = path;
     path.append(name);
+    if (path.exists())
+    {
+        videoEncodingError("Video encoding failure, output file already exists: " + path.str());
+        return false;
+    }
     path_link.append(name_link);
     path_link.remove();
     bool ok = path_link.makeLink(path.file());
@@ -464,7 +469,9 @@ void FGViewMgr::video_start(
     catch (std::exception& e)
     {
         videoEncodingError(e.what());
+        return false;
     }
+    return true;
 }
 
 void FGViewMgr::video_stop()

src/Viewer/viewmgr.hxx

@@ -94,25 +94,38 @@ public:
 
     void add_view( flightgear::View * v );
 
-    // Start video encoding to <path>.
+    // Start video encoding of main window.
     //
-    // If <name> is "" we generate a name containing current date and time.
+    //  name
-    //
+    //      Name of output file or "" to generate a name containing current
-    // If <codec> is "" we use /sim/video/codec.
+    //      date and time and /sim/video/container. List of supported
-    //
+    //      containers can be found with 'ffmpeg -formats'.
-    // If quality is -1 we use /sim/video/quality; similarly for speed. If
+    //  codec_name
-    // bitrate is 0 we use /sim/video/bitrate.
+    //      Name of codec or "" to use /sim/video/codec. Passed to
+    //      avcodec_find_encoder_by_name(). List of supported codecs can be
+    //      found with 'ffmpeg -codecs'.
+    //  quality
+    //      Encoding quality in range 0..1 or -1 to use /sim/video/quality.
+    //  speed:
+    //      Encoding speed in range 0..1 or -1 to use /sim/video/speed.
+    //    bitrate
+    //      Target bitratae in bits/sec or -1 to use /sim/video/bitrate.
     //
     // We show popup warning if values are out of range - quality and speed
     // must be -1 or 0-1, bitrate must be >= 0.
     //
-    void video_start(
+    // Returns false if we fail to start video encoding.
-            const std::string& name,
+    //
-            const std::string& codec,
+    bool video_start(
-            double quality,
+            const std::string& name="",
-            double speed,
+            const std::string& codec="",
-            int bitrate
+            double quality=-1,
+            double speed=-1,
+            int bitrate=0
             );
+    
+    // Stop video encoding of main window.
+    //
     void video_stop();
 
 private: