Translate OPEN_EXR DNA image format enum to EXR for CLI

Blender's `--render-format` CLI parameter generally takes the same names
as the `bpy.context.scene.render.image_settings.file_format` DNA parameter,
except when it comes to OpenEXR.

See https://developer.blender.org/D4502 for a proposal to make this
consistent.

flamenco_worker/commands.py

@@ -805,6 +805,20 @@ class AbstractBlenderCommand(AbstractSubprocessCommand):
 
         self._last_activity_time = 0.0
 
+    def _format_dna_to_cli(self, format_for_dna: str) -> str:
+        """Converts the DNA image format enum to a CLI -F argument for Blender.
+
+        The DNA enum value is generally the same as what would be passed on the
+        command line, except the EXR formats.
+        """
+
+        # See https://developer.blender.org/D4502
+        dna_to_cli = {
+            'OPEN_EXR': 'EXR',
+            'OPEN_EXR_MULTILAYER': 'MULTILAYER',
+        }
+        return dna_to_cli.get(format_for_dna, format_for_dna)
+
     def validate(self, settings: Settings):
         blender_cmd, err = self._setting(settings, 'blender_cmd', True)
         if err:
@@ -979,7 +993,7 @@ class BlenderRenderCommand(AbstractBlenderCommand):
         if settings.get('render_output'):
             cmd.extend(['--render-output', settings['render_output']])
         if settings.get('format'):
-            cmd.extend(['--render-format', settings['format']])
+            cmd.extend(['--render-format', self._format_dna_to_cli(settings['format'])])
         if settings.get('frames'):
             cmd.extend(['--render-frame', settings['frames']])
         return cmd

tests/test_commands_blender_render.py

@@ -108,6 +108,40 @@ class BlenderRenderTest(AbstractCommandTest):
                 stderr=subprocess.STDOUT,
             )
 
+    def test_cli_openexr(self):
+        from tests.mock_responses import CoroMock
+
+        filepath = Path(__file__).parent.as_posix()
+        settings = {
+            # Point blender_cmd to this file so that we're sure it exists.
+            'blender_cmd': f'{self.thisfile!r} --with --cli="args for CLI"',
+            'chunk_size': 100,
+            'frames': '1..2',
+            'format': 'OPEN_EXR',
+            'filepath': filepath,
+        }
+
+        cse = CoroMock(...)
+        cse.coro.return_value.wait = CoroMock(return_value=0)
+        cse.coro.return_value.pid = 47
+        with patch('asyncio.create_subprocess_exec', new=cse) as mock_cse:
+            self.loop.run_until_complete(self.cmd.run(settings))
+
+            mock_cse.assert_called_once_with(
+                self.thisfile,
+                '--with',
+                '--cli=args for CLI',
+                '--enable-autoexec',
+                '-noaudio',
+                '--background',
+                filepath,
+                '--render-format', 'EXR',  # see https://developer.blender.org/D4502
+                '--render-frame', '1..2',
+                stdin=subprocess.DEVNULL,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.STDOUT,
+            )
+
     def test_python_expr(self):
         from tests.mock_responses import CoroMock