[fragment,hls,f4m,dash,ism] improve fragment downloading

- resume immediately
- no need to concatenate segments and decrypt them on every resume
- no need to save temp files for segments

and for hls downloader:
- no need to download keys for segments that already downloaded

1 files changed, 11 insertions, 32 deletions

diff --git a/youtube_dl/downloader/dash.py b/youtube_dl/downloader/dash.py
index e2ddc369e..94a13a543 100644
--- a/youtube_dl/downloader/dash.py
+++ b/youtube_dl/downloader/dash.py
@@ -1,13 +1,7 @@
 from __future__ import unicode_literals
 
-import os
-
 from .fragment import FragmentFD
 from ..compat import compat_urllib_error
-from ..utils import (
-    sanitize_open,
-    encodeFilename,
-)
 
 
 class DashSegmentsFD(FragmentFD):
@@ -28,31 +22,24 @@ class DashSegmentsFD(FragmentFD):
 
         self._prepare_and_start_frag_download(ctx)
 
-        segments_filenames = []
-
         fragment_retries = self.params.get('fragment_retries', 0)
         skip_unavailable_fragments = self.params.get('skip_unavailable_fragments', True)
 
-        def process_segment(segment, tmp_filename, num):
-            segment_url = segment['url']
-            segment_name = 'Frag%d' % num
-            target_filename = '%s-%s' % (tmp_filename, segment_name)
+        frag_index = 0
+        for i, segment in enumerate(segments):
+            frag_index += 1
+            if frag_index <= ctx['frag_index']:
+                continue
             # In DASH, the first segment contains necessary headers to
             # generate a valid MP4 file, so always abort for the first segment
-            fatal = num == 0 or not skip_unavailable_fragments
+            fatal = i == 0 or not skip_unavailable_fragments
             count = 0
             while count <= fragment_retries:
                 try:
-                    success = ctx['dl'].download(target_filename, {
-                        'url': segment_url,
-                        'http_headers': info_dict.get('http_headers'),
-                    })
+                    success, frag_content = self._download_fragment(ctx, segment['url'], info_dict)
                     if not success:
                         return False
-                    down, target_sanitized = sanitize_open(target_filename, 'rb')
-                    ctx['dest_stream'].write(down.read())
-                    down.close()
-                    segments_filenames.append(target_sanitized)
+                    self._append_fragment(ctx, frag_content)
                     break
                 except compat_urllib_error.HTTPError as err:
                     # YouTube may often return 404 HTTP error for a fragment causing the
@@ -63,22 +50,14 @@ class DashSegmentsFD(FragmentFD):
                     # HTTP error.
                     count += 1
                     if count <= fragment_retries:
-                        self.report_retry_fragment(err, segment_name, count, fragment_retries)
+                        self.report_retry_fragment(err, frag_index, count, fragment_retries)
             if count > fragment_retries:
                 if not fatal:
-                    self.report_skip_fragment(segment_name)
-                    return True
+                    self.report_skip_fragment(frag_index)
+                    continue
                 self.report_error('giving up after %s fragment retries' % fragment_retries)
                 return False
-            return True
-
-        for i, segment in enumerate(segments):
-            if not process_segment(segment, ctx['tmpfilename'], i):
-                return False
 
         self._finish_frag_download(ctx)
 
-        for segment_file in segments_filenames:
-            os.remove(encodeFilename(segment_file))
-
         return True