Enable interrupt/resume of MP4 streams

- skipping the processing of an existing target output file
- skipping the download of an existing target stream file
- resume the download of an existing target stream temporary file
  using a HTTP range request

src/delarte/__init__.py

@@ -132,6 +132,11 @@ def download_targets(targets, http_session, on_progress):
     from .muxing import mux_target
 
     for target in targets:
+        output_path = f"{target.output}.mkv"
+
+        if os.path.isfile(output_path):
+            print(f"Skipping {output_path!r}")
+            continue
 
         video_path = target.output + ".video.mp4"
         audio_path = target.output + ".audio.mp4"

src/delarte/download.py

@@ -19,10 +19,14 @@ def download_mp4_media(url, file_name, http_session, on_progress):
 
     temp_file = f"{file_name}.tmp"
 
-    with open(temp_file, "w+b") as f:
-        r = http_session.get(url, timeout=5, stream=True)
+    with open(temp_file, "ab") as f:
+        r = http_session.get(
+            url, timeout=5, stream=True, headers={"Range": f"bytes={f.tell()}-"}
+        )
         r.raise_for_status()
-        total = int(r.headers["content-length"])
+
+        _, total = r.headers["content-range"].split("/")
+        total = int(total)
 
         for content in r.iter_content(_CHUNK):
             f.write(content)