VSE: Python API, allow creation of VSE Movie strips with missing file

It was already possible to create Sound and Image strips that reference
non-existing files. Now it's also possible to create Movie strips
referencing missing files via the Python API call
`Sequences.new_movie()`. In this case, the duration of the strip will be
set to 1 frame.

Note that this commit does not change anything in the user interface.

The Python API of the `MovieStrip` class is extended with a function
`reload_if_needed()`. This function only performs disk I/O if the movie
strip cannot produce frames, that is either when its filepath points to
a non-existing file, or when the video sequence editor has not been
shown yet (for example because it is in an inactive workspace).

This allows for the following:

```
import bpy

scene = bpy.context.scene
vse = scene.sequence_editor_create()

filepath = bpy.path.abspath('//demo.mkv')
strip = vse.sequences.new_movie("movie", filepath,
    channel=2,
    frame_start=47,
    file_must_exist=False)
strip.frame_final_end = 327
```

This will create a new movie strip, even when `demo.mkv` does not exist.

Once `demo.mkv` has appeared at the expected location, either
`strip.reload_if_needed()` or `strip.filepath = strip.filepath` will
load it.

Differential Revision: https://developer.blender.org/D8257

Reviewed By: Sergey, ISS

1 files changed, 26 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_sequencer.c b/source/blender/makesrna/intern/rna_sequencer.c
index 7342879e9e6..de225e3c685 100644
--- a/source/blender/makesrna/intern/rna_sequencer.c
+++ b/source/blender/makesrna/intern/rna_sequencer.c
@@ -749,6 +749,25 @@ static IDProperty *rna_Sequence_idprops(PointerRNA *ptr, bool create)
   return seq->prop;
 }
 
+static bool rna_MovieSequence_reload_if_needed(ID *scene_id, Sequence *seq, Main *bmain)
+{
+  Scene *scene = (Scene *)scene_id;
+  bool has_reloaded;
+  bool can_produce_frames;
+
+  BKE_sequence_movie_reload_if_needed(bmain, scene, seq, &has_reloaded, &can_produce_frames);
+
+  if (has_reloaded && can_produce_frames) {
+    BKE_sequence_calc(scene, seq);
+    BKE_sequence_invalidate_cache_raw(scene, seq);
+
+    DEG_id_tag_update(&scene->id, ID_RECALC_SEQUENCER_STRIPS);
+    WM_main_add_notifier(NC_SCENE | ND_SEQUENCER, scene);
+  }
+
+  return can_produce_frames;
+}
+
 static PointerRNA rna_MovieSequence_metadata_get(Sequence *seq)
 {
   if (seq == NULL || seq->anims.first == NULL) {
@@ -2385,6 +2404,13 @@ static void rna_def_movie(BlenderRNA *brna)
                                 "rna_Sequence_filepath_set");
   RNA_def_property_update(prop, NC_SCENE | ND_SEQUENCER, "rna_Sequence_filepath_update");
 
+  func = RNA_def_function(srna, "reload_if_needed", "rna_MovieSequence_reload_if_needed");
+  RNA_def_function_flag(func, FUNC_USE_SELF_ID | FUNC_USE_MAIN);
+  /* return type */
+  parm = RNA_def_boolean(
+      func, "can_produce_frames", 0, "True if the strip can produce frames, False otherwise", "");
+  RNA_def_function_return(func, parm);
+
   /* metadata */
   func = RNA_def_function(srna, "metadata", "rna_MovieSequence_metadata_get");
   RNA_def_function_ui_description(func, "Retrieve metadata of the movie file");