Workaround for FFmpeg not supporting '-pattern_type glob' on Windows

Globbing is the only way in which we can convert arbitrary frame sequences
to a video; the other input options all assume that the frame numbers are
sequential, and stop at the first gap. Globbing just skips gaps and
actually uses all available frames.

The workaround consist of doing the globbing in Python and creating an
index file that lists all the input files.

flamenco_worker/commands.py

@@ -6,6 +6,7 @@ import asyncio.subprocess
 import datetime
 import logging
 import pathlib
+import platform
 import re
 import shlex
 import shutil
@@ -1026,6 +1027,7 @@ class BlenderRenderAudioCommand(BlenderRenderCommand):
 
 
 class AbstractFFmpegCommand(AbstractSubprocessCommand, abc.ABC):
+    index_file: typing.Optional[pathlib.Path] = None
 
     def validate(self, settings: Settings) -> typing.Optional[str]:
         # Check that FFmpeg can be found and shlex-split the string.
@@ -1045,6 +1047,14 @@ class AbstractFFmpegCommand(AbstractSubprocessCommand, abc.ABC):
         cmd = self._build_ffmpeg_command(settings)
         await self.subprocess(cmd)
 
+        if self.index_file is not None and self.index_file.exists():
+            try:
+                self.index_file.unlink()
+            except IOError:
+                msg = f'unable to unlink file {self.index_file}, ignoring'
+                await self.worker.register_log(msg)
+                self._log.warning(msg)
+
     def _build_ffmpeg_command(self, settings: Settings) -> typing.List[str]:
         assert isinstance(settings['ffmpeg_cmd'], list), \
             'run validate() before _build_ffmpeg_command'
@@ -1063,6 +1073,30 @@ class AbstractFFmpegCommand(AbstractSubprocessCommand, abc.ABC):
         """
         pass
 
+    def create_index_file(self, input_files: pathlib.Path) -> pathlib.Path:
+        """Construct a list of filenames for ffmpeg to process.
+
+        The filenames are stored in a file 'ffmpeg-input.txt' that sits in the
+        same directory as the input files.
+
+        It is assumed that 'input_files' contains a glob pattern in the file
+        name, and not in any directory parts.
+
+        The index file will be deleted after successful execution of the ffmpeg
+        command.
+        """
+
+        # The index file needs to sit next to the input files, as
+        # ffmpeg checks for 'unsafe paths'.
+        self.index_file = input_files.absolute().with_name('ffmpeg-input.txt')
+
+        with self.index_file.open('w') as outfile:
+            for file_path in sorted(input_files.parent.glob(input_files.name)):
+                escaped = str(file_path.name).replace("'", "\\'")
+                print("file '%s'" % escaped, file=outfile)
+
+        return self.index_file
+
 
 @command_executor('create_video')
 class CreateVideoCommand(AbstractFFmpegCommand):
@@ -1100,10 +1134,27 @@ class CreateVideoCommand(AbstractFFmpegCommand):
         return None
 
     def ffmpeg_args(self, settings: Settings) -> typing.List[str]:
+        input_files = Path(settings['input_files'])
+
         args = [
-            '-pattern_type', 'glob',
             '-r', str(settings['fps']),
-            '-i', settings['input_files'],
+        ]
+
+        if platform.system() == 'Windows':
+            # FFMpeg on Windows doesn't support globbing, so we have to do
+            # that in Python instead.
+            index_file = self.create_index_file(input_files)
+            args += [
+                '-f', 'concat',
+                '-i', index_file.as_posix(),
+            ]
+        else:
+            args += [
+                '-pattern_type', 'glob',
+                '-i', input_files.as_posix(),
+            ]
+
+        args += [
             '-c:v', self.codec_video,
             '-crf', str(self.constant_rate_factor),
             '-g', str(self.keyframe_interval),
@@ -1124,8 +1175,6 @@ class ConcatenateVideosCommand(AbstractFFmpegCommand):
     Requires FFmpeg to be installed and available with the 'ffmpeg' command.
     """
 
-    index_file: typing.Optional[Path] = None
-
     def validate(self, settings: Settings) -> typing.Optional[str]:
         err = super().validate(settings)
         if err:
@@ -1143,35 +1192,15 @@ class ConcatenateVideosCommand(AbstractFFmpegCommand):
 
         return None
 
-    async def execute(self, settings: Settings) -> None:
-        await super().execute(settings)
-
-        if self.index_file is not None and self.index_file.exists():
-            try:
-                self.index_file.unlink()
-            except IOError:
-                msg = f'unable to unlink file {self.index_file}, ignoring'
-                await self.worker.register_log(msg)
-                self._log.warning(msg)
-
     def ffmpeg_args(self, settings: Settings) -> typing.List[str]:
-        input_files = Path(settings['input_files']).absolute()
-        self.index_file = input_files.with_name('ffmpeg-input.txt')
-
-        # Construct the list of filenames for ffmpeg to process.
-        # The index file needs to sit next to the input files, as
-        # ffmpeg checks for 'unsafe paths'.
-        with self.index_file.open('w') as outfile:
-            for video_path in sorted(input_files.parent.glob(input_files.name)):
-                escaped = str(video_path.name).replace("'", "\\'")
-                print("file '%s'" % escaped, file=outfile)
+        index_file = self.create_index_file(Path(settings['input_files']))
 
         output_file = Path(settings['output_file'])
         self._log.debug('Output file: %s', output_file)
 
         args = [
             '-f', 'concat',
-            '-i', self.index_file.as_posix(),
+            '-i', index_file.as_posix(),
             '-c', 'copy',
             '-y',
             output_file.as_posix(),

tests/test_commands_create_video.py

@@ -2,6 +2,7 @@ import logging
 import shutil
 import typing
 from pathlib import Path
+import platform
 import shlex
 import subprocess
 import sys
@@ -48,11 +49,21 @@ class CreateVideoTest(AbstractCommandTest):
         self.cmd.validate(self.settings)
         cliargs = self.cmd._build_ffmpeg_command(self.settings)
 
+        if platform.system() == 'Windows':
+            input_args = [
+                '-f', 'concat',
+                '-i', Path(self.settings['input_files']).absolute().with_name('ffmpeg-input.txt').as_posix(),
+            ]
+        else:
+            input_args = [
+                '-pattern_type', 'glob',
+                '-i', '/tmp/*.png',
+            ]
+
         self.assertEqual([
             Path(sys.executable).absolute().as_posix(), '-hide_banner',
-            '-pattern_type', 'glob',
             '-r', '24',
-            '-i', '/tmp/*.png',
+            *input_args,
             '-c:v', 'h264',
             '-crf', '23',
             '-g', '18',