mirror-yt: Handle returncode 1

We switch from `subprocess.run` to manually handling a `Popen` object so
we can decide whether a returncode of 1 is fine or now depending on the
output we see. Since we want live output during the download, we cannot
just capture all the output. Instead, we have to regularly print
whatever we captured. Therefore, we need a `Popen` object and need to
call `communicate()` with a timeout on it.

mirror-yt.py

@@ -60,7 +60,28 @@ def download(allow_unknown, base_dir, channel_file):
             '--write-thumbnail',
             url
         ]
-        subprocess.run(cmd, check=True, cwd=target_dir) 
+        p = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, cwd=target_dir)
+        prev_output = ''
+        while p.poll() is None:
+            try:
+                stdout_data, stderr_data = p.communicate(timeout=0.5)
+            except subprocess.TimeoutExpired as e:
+                if e.output:
+                    print(e.output[len(prev_output):].decode('utf-8'), end='')
+                prev_output = e.output or ''
+            else:
+                print(stdout_data[len(prev_output):].decode('utf-8'))
+
+        stdout_lines = stdout_data.decode('utf-8').splitlines()
+        if p.returncode == 0:
+            return
+        if p.returncode == 101:
+            pass
+        elif p.returncode == 1 and stdout_lines[-1] and 'Finished downloading playlist' in stdout_lines[-1]:
+            pass
+        else:
+            breakpoint()
+            raise subprocess.CalledProcessError(returncode=p.returncode, cmd=cmd)
 
         sleep_seconds = 5
         print(f"Sleeping {sleep_seconds}s")