chore(deps): remove subprocess calls to FFMPEG with av

Linked to the progess made in ManimCommunity/manim#3501.

The following PR aims at reducing subprocess calls for security and speed reasons. Also, with ManimCommunity/manim#3501 is merged, FFMPEG should not be needed anymore as it is part of `PyAv`.

manim_slides/logger.py

@@ -40,6 +40,7 @@ def make_logger() -> logging.Logger:
     logger = logging.getLogger("manim-slides")
     logger.setLevel(logging.getLogger("manim").level)
     logger.addHandler(rich_handler)
+    logging.getLogger("libav").addHandler(rich_handler)
 
     return logger
 

manim_slides/utils.py

@@ -1,45 +1,37 @@
 import hashlib
-import subprocess
 import tempfile
 from pathlib import Path
 from typing import List
 
+import av
+
 from .logger import logger
 
 
-def concatenate_video_files(ffmpeg_bin: Path, files: List[Path], dest: Path) -> None:
+def concatenate_video_files(_: Path, files: List[Path], dest: Path) -> None:
     """Concatenate multiple video files into one."""
     f = tempfile.NamedTemporaryFile(mode="w", delete=False)
     f.writelines(f"file '{path.absolute()}'\n" for path in files)
     f.close()
 
-    command: List[str] = [
-        str(ffmpeg_bin),
-        "-f",
-        "concat",
-        "-safe",
-        "0",
-        "-i",
-        f.name,
-        "-c",
-        "copy",
-        str(dest),
-        "-y",
-    ]
-    logger.debug(" ".join(command))
-    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-    output, error = process.communicate()
-
-    if output:
-        logger.debug(output.decode())
-
-    if error:
-        logger.debug(error.decode())
-
-    if not dest.exists():
-        raise ValueError(
-            "could not properly concatenate files, use `-v DEBUG` for more details"
-        )
+    input_ = av.open(f.name, options={"safe": "0"}, format="concat")
+    input_stream = input_.streams.video[0]
+    output = av.open(str(dest), mode="w")
+    output_stream = output.add_stream(
+        template=input_stream,
+    )
+
+    for packet in input_.demux(input_stream):
+        # We need to skip the "flushing" packets that `demux` generates.
+        if packet.dts is None:
+            continue
+
+        # We need to assign the packet to the new stream.
+        packet.stream = output_stream
+        output.mux(packet)
+
+    input_.close()
+    output.close()
 
 
 def merge_basenames(files: List[Path]) -> Path:
@@ -63,15 +55,48 @@ def merge_basenames(files: List[Path]) -> Path:
     return dirname.joinpath(basename + ext)
 
 
-def reverse_video_file(ffmpeg_bin: Path, src: Path, dst: Path) -> None:
-    """Reverses a video file, writting the result to `dst`."""
-    command = [str(ffmpeg_bin), "-y", "-i", str(src), "-vf", "reverse", str(dst)]
-    logger.debug(" ".join(command))
-    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
-    output, error = process.communicate()
-
-    if output:
-        logger.debug(output.decode())
-
-    if error:
-        logger.debug(error.decode())
+def link_nodes(*nodes: av.filter.context.FilterContext) -> None:
+    """Code from https://github.com/PyAV-Org/PyAV/issues/239."""
+    for c, n in zip(nodes, nodes[1:]):
+        c.link_to(n)
+
+
+def reverse_video_file(_: Path, src: Path, dest: Path) -> None:
+    """Reverses a video file, writting the result to `dest`."""
+    input_ = av.open(str(src))
+    input_stream = input_.streams.video[0]
+    output = av.open(str(dest), mode="w")
+    output_stream = output.add_stream(
+        codec_name=input_stream.codec_context.name,
+        rate=input_stream.base_rate
+    )
+    output_stream.width = input_stream.width
+    output_stream.height = input_stream.height
+    output_stream.pix_fmt = input_stream.pix_fmt
+
+    graph = av.filter.Graph()
+    link_nodes(
+            graph.add_buffer(template=input_stream),
+            graph.add("reverse"),
+            graph.add("buffersink"),
+    )
+    graph.configure()
+
+    frames_count = 0
+    for packet in input_.demux(input_stream):
+        for frame in packet.decode():
+            graph.push(frame)
+            frames_count += 1
+
+    graph.push(None)
+
+    for i in range(frames_count):
+        frame = graph.pull()
+        for packet in output_stream.encode(frame):
+            output.mux(packet)
+
+    for packet in output_stream.encode():
+        output.mux(packet)
+
+    input_.close()
+    output.close()