Add option `--throttled-rate` below which video data is re-extracted

Currently only for HTTP downloads

Closes #430, workaround for https://github.com/ytdl-org/youtube-dl/issues/29326

2 files changed, 18 insertions, 2 deletions

diff --git a/yt_dlp/downloader/common.py b/yt_dlp/downloader/common.py
index 66e9677ed..65751bb3b 100644
--- a/yt_dlp/downloader/common.py
+++ b/yt_dlp/downloader/common.py
@@ -14,6 +14,7 @@ from ..utils import (
     format_bytes,
     shell_quote,
     timeconvert,
+    ThrottledDownload,
 )
 
 
@@ -32,6 +33,7 @@ class FileDownloader(object):
     verbose:            Print additional info to stdout.
     quiet:              Do not print messages to stdout.
     ratelimit:          Download speed limit, in bytes/sec.
+    throttledratelimit: Assume the download is being throttled below this speed (bytes/sec)
     retries:            Number of times to retry for HTTP error 5xx
     buffersize:         Size of download buffer in bytes.
     noresizebuffer:     Do not automatically resize the download buffer.
@@ -170,7 +172,7 @@ class FileDownloader(object):
     def slow_down(self, start_time, now, byte_counter):
         """Sleep if the download speed is over the rate limit."""
         rate_limit = self.params.get('ratelimit')
-        if rate_limit is None or byte_counter == 0:
+        if byte_counter == 0:
             return
         if now is None:
             now = time.time()
@@ -178,7 +180,7 @@ class FileDownloader(object):
         if elapsed <= 0.0:
             return
         speed = float(byte_counter) / elapsed
-        if speed > rate_limit:
+        if rate_limit is not None and speed > rate_limit:
             sleep_time = float(byte_counter) / rate_limit - elapsed
             if sleep_time > 0:
                 time.sleep(sleep_time)
diff --git a/yt_dlp/downloader/http.py b/yt_dlp/downloader/http.py
index bf77f4427..15eb54aab 100644
--- a/yt_dlp/downloader/http.py
+++ b/yt_dlp/downloader/http.py
@@ -18,6 +18,7 @@ from ..utils import (
     int_or_none,
     sanitize_open,
     sanitized_Request,
+    ThrottledDownload,
     write_xattr,
     XAttrMetadataError,
     XAttrUnavailableError,
@@ -223,6 +224,7 @@ class HttpFD(FileDownloader):
             # measure time over whole while-loop, so slow_down() and best_block_size() work together properly
             now = None  # needed for slow_down() in the first loop run
             before = start  # start measuring
+            throttle_start = None
 
             def retry(e):
                 to_stdout = ctx.tmpfilename == '-'
@@ -313,6 +315,18 @@ class HttpFD(FileDownloader):
                 if data_len is not None and byte_counter == data_len:
                     break
 
+                if speed and speed < (self.params.get('throttledratelimit') or 0):
+                    # The speed must stay below the limit for 3 seconds
+                    # This prevents raising error when the speed temporarily goes down
+                    if throttle_start is None:
+                        throttle_start = now
+                    elif now - throttle_start > 3:
+                        if ctx.stream is not None and ctx.tmpfilename != '-':
+                            ctx.stream.close()
+                        raise ThrottledDownload()
+                else:
+                    throttle_start = None
+
             if not is_test and ctx.chunk_size and ctx.data_len is not None and byte_counter < ctx.data_len:
                 ctx.resume_len = byte_counter
                 # ctx.block_size = block_size