mtime is today's date on muxed video files

[ivan]

The mtime on the video file is correct when not muxing, but is today's date when muxing:

# PYTHONPATH=. python -m youtube_dl -f best "VuSNIbhzuAU"
[youtube] Confirming age
[youtube] VuSNIbhzuAU: Downloading webpage
[youtube] VuSNIbhzuAU: Downloading video info webpage
[youtube] VuSNIbhzuAU: Extracting video information
[youtube] VuSNIbhzuAU: Downloading DASH manifest
[download] Destination: Flood on Regent Street-VuSNIbhzuAU.mp4
[download] 100% of 17.90MiB in 00:16

# ls -l Flood\ on\ Regent\ Street-VuSNIbhzuAU.mp4        
-rw-rw-r-- 1 at at 18,773,958 2014-02-16 18:55 Flood on Regent Street-VuSNIbhzuAU.mp4

# rm Flood\ on\ Regent\ Street-VuSNIbhzuAU.mp4 

# PYTHONPATH=. python -m youtube_dl -f bestvideo+bestaudio "VuSNIbhzuAU"       
[youtube] Confirming age
[youtube] VuSNIbhzuAU: Downloading webpage
[youtube] VuSNIbhzuAU: Downloading video info webpage
[youtube] VuSNIbhzuAU: Extracting video information
[youtube] VuSNIbhzuAU: Downloading DASH manifest
[download] Destination: Flood on Regent Street-VuSNIbhzuAU.f137.mp4
[download] 100% of 23.13MiB in 00:28
[download] Destination: Flood on Regent Street-VuSNIbhzuAU.f141.m4a
[download] 100% of 1.43MiB in 00:02
[ffmpeg] Merging formats into "Flood on Regent Street-VuSNIbhzuAU.mp4"

# ls -l Flood\ on\ Regent\ Street-VuSNIbhzuAU.mp4 
-rw-rw-r-- 1 at at 25,754,469 2014-11-20 04:33 Flood on Regent Street-VuSNIbhzuAU.mp4

Expected 2014-02-16, but got today's date 2014-11-20 instead.

# avconv 
avconv version 9.16-6:9.16-0ubuntu0.14.04.1, Copyright (c) 2000-2014 the Libav developers
  built on Aug 10 2014 18:16:02 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
Hyper fast Audio and Video encoder
usage: avconv [options] [[infile options] -i infile]... {[outfile options] outfile}...

Use -h to get full help or, even better, run 'man avconv'