set mtime to video publish date

[codl]

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Description of your issue, suggested solution and other information

this is a followup to #18383 in which I found out that the mtime is only set according to the Last-Modified HTTP headers, and doesn't work for videos downloaded with DASH. I find this counter-intuitive: having downloaded videos and seen that the mtime was set to — as far as I could tell — the upload date, I expected this to happen all the time until it randomly didn't work for some videos.

I think that, whenever the upload time is available, it should be used for the final file's mtime in place of Last-Modified.

[dotysan]

I just tested and it appears that all DASH segments indeed had the same/proper mtime when fetched via http.py. However when the segments are stitched together, the mtime is lost.

[dotysan]

Not a pull request yet, because I'm new to the code in this project and haven't run the unit tests. But this seems to do the job!

diff --git a/youtube_dl/downloader/fragment.py b/youtube_dl/downloader/fragment.py
index 917f6dc01..37edcc900 100644
--- a/youtube_dl/downloader/fragment.py
+++ b/youtube_dl/downloader/fragment.py
@@ -116,6 +116,10 @@ class FragmentFD(FileDownloader):
         finally:
             if self.__do_ytdl_file(ctx):
                 self._write_ytdl_file(ctx)
+            try:
+                os.utime(ctx['tmpfilename'], (time.time(), os.stat(ctx['fragment_filename_sanitized']).st_mtime))
+            except Exception:
+                pass
             if not self.params.get('keep_fragments', False):
                 os.remove(encodeFilename(ctx['fragment_filename_sanitized']))
             del ctx['fragment_filename_sanitized']

In summary, it leverages the fact that every fragment/segment already has an mtime set from the last-modified header. So it just re-sets the mtime of the working/temp file from the fragment file. Which in turn, seems to be preserved in the finalized file of all fragments.

Feedback?

[reallyuniquename]

Has this been addressed? I'm running latest version and it seems mtime has no effect on fragmented Twitch VODs.