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Re: [Bug-wget] wget Tutorial


From: Tim Rühsen
Subject: Re: [Bug-wget] wget Tutorial
Date: Wed, 2 Aug 2017 12:55:30 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

Hi Frederick,

please always write to the mailing list, private mail only if it is
about private things ;-)

I read a bit the ISO/IEC 23009-1:2014 spec (Information technology --
Dynamic adaptive streaming over HTTP (DASH) -- Part 1: Media
presentation description and segment formats).


In short: The worst way of streaming data I have ever seen (totally
blown up) !

Anyways, it's all about (real) timing. The file names can be
'calculated' by some very obscure formula using some details from the
client_manifest.mpd and the current time. If any of those values in the
mpd file ever change, the file names will be totally different.

On *nix you can use the following script to download/record the stream:

########################
#!/bin/bash

outfile="bbc2017-07-30.mp4"

rm -f $outfile
wget -q -O-
http://vs-dash-ww-rd-live.bbcfmt.hs.llnwd.net:80/al/lossless/A1/IS.mp4
>$outfile

lastseq=$(expr $(date +%s) '*' 100 / 384 - 32)
seq=$lastseq

while true; do
  # wait for seq to change - then we have 3.84s to download it
  while test $seq = $lastseq; do
    sleep 0.5
    seq=$(expr $(date +%s) '*' 100 / 384 - 32)
  done
  lastseq=$seq
  wget -q -O-
http://vs-dash-ww-rd-live.bbcfmt.hs.llnwd.net:80/al/lossless/A1/${seq}.m4s
>>$outfile
  ls -la $outfile
done
########################


This won't work if you have a clock skew or a slow bandwidth.

Have fun with it !

With Best Regards, Tim



On 08/02/2017 02:52 AM, Frederick George Wilson wrote:
> Dear Tim,
> 
> I wrote a tutorial on listening to the BBC Proms 2017 via wget:
> https://archive.org/download/70075/2017-07-31-updated-tutorial-BBC-MPEG-DASH-FLAC.txt
> which is listed on the Internet Archive item details page:
> http://archive.org/details/70075 .
> 
> The -w 3 and --random-wait command line elements work most of the time --
> however, during particularly slow or quiet stretches of music or spoken
> word, the 404 Not Found errors pile up as wget runs ahead of the stream, or
> conversely, dense stretches of music cause wget to lag behind.  I've tried
> with -w 2 and -w 4, but neither of those ever captures more than a few
> minutes.
> 
> Any suggestions?
> 
> 
> Many Thanks,
> FW
> 

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