Archive for April 8th, 2011

Convert WAV to MP3 in command line with LAME on Linux

Friday, April 8th, 2011

I needed to convert a bunch of files from WAV to MP3 format on my Linux desktop.

I’ve placed all my wav files to the directory /home/hipo/wav

And then I issued the small one liner script to convert the .wav files to .mp3 using the niftly lame linux mp3 convertor.

Here is how I did it:

linux-desktop:~$ cd wav
linux-desktop:/home/hipo/wav$ for i in *.wav; do
new_name=$(echo $i |sed -e 's#wav#mp3#g');
lame -V0 -h -b 160 --vbr-new "$i" "$new_name";
done

After executing the little script you might go and have a coffee, if you have thousands of files, each file convertion takes about 10-15 seconds of time (speed depends on your CPU).

Here is some output from a lame convertion to mp3 taking place:

Encoding as 8 kHz single-ch MPEG-2.5 Layer III VBR(q=0)
Frame | CPU time/estim | REAL time/estim | play/CPU | ETA
27237/27237 (100%)| 0:12/ 0:12| 0:12/ 0:12| 155.89x| 0:00
64 [27237] ***************************************************************
----------------------------------------------
kbps mono % long switch short %
64.0 100.0 84.1 8.9 7.0
If you want to save my convertion quickly for a later, download my Convert WAV to mp3 from a directory with lame shell script here

Actually there are plenty of other ways to convert wav to mp3 on Linux through mplayer, ffmpeg even with mpg123.

There are also some GUI programs that could do the convertion like winff , however for some weird reason after installing WinFF on my debian it was not able to complete convertion to mp3?!
But it doesn’t matter, the good news is I did what I wanted to via the simple lame program and the above script, hope it helps somebody out there.

How to enable output compression (gzipfile content compression) in nginx webserver

Friday, April 8th, 2011

I have recently installed and configured a Debian Linux server with nginx
. Since then I’ve been testing around different ways to optimize the nginx performance.

In my nginx quest, one of the most crucial settings which dramatically improved the end client performance was enabling the so called output compression which in Apache based servers is also known as content gzip compression .
In Apache webservers the content gzip compression is provided by a server module called mod_deflate .

The output compression nginx settings saves a lot of bandwidth and though it adds up a bit more load to the server, the plain text files like html, xml, js and css’s download time reduces drasticly as they’re streamed to the browser in gzip compressed format.
This little improvement in download speed also does impact the overall end user browser experience and therefore improves the browsing speed experience with websites.

If you have already had experience nginx you already know it is a bit fastidious and you have to be very careful with it’s configuration, however thanksfully enabling the gzip compression was actually rather easier than I thought.

Here is what I added in my nginx config to enable output compression:

## Compression
gzip on;
gzip_buffers 16 8k;
gzip_comp_level 9;
gzip_http_version 1.1;
gzip_min_length 0;
gzip_vary on;

Important note here is that need to add this code in the nginx configuration block starting with:

http {
....
## Compression
gzip on;
gzip_buffers 16 8k;
gzip_comp_level 9;
gzip_http_version 1.1;
gzip_min_length 0;
gzip_vary on;

In order to load the gzip output compression as a next step you need to restart the nginx server, either by it’s init script if you use one or by killing the old nginx server instances and starting up the nginx server binary again:
I personally use an init script, so restarting nginx for me is done via the cmd:

debian:~# /etc/init.d/nginx restart
Restarting nginx: nginx.

Now to test if the output gzip compression is enabled for nginx, you can simply use telnet

hipo@linux:~$ telnet your-nginx-webserver-domain.com 80
Escape character is '^]'.

After the Escape character is set ‘^]’ appears on your screen type in the blank space:

HEAD / HTTP/1.0

and press enter twice.
The output which should follow should look like:


HTTP/1.1 200 OK
Server: nginx
Date: Fri, 08 Apr 2011 12:04:43 GMT
Content-Type: text/html
Content-Length: 13
Last-Modified: Tue, 22 Mar 2011 15:04:26 GMT
Connection: close
Vary: Accept-Encoding
Expires: Fri, 15 Apr 2011 12:04:43 GMT
Cache-Control: max-age=604800
Accept-Ranges: bytes

The whole transaction with telnet command issued and the nginx webserver output should look like so:

hipo@linux:~$ telnet your-nginx-webserver-domain.com 80
Trying xxx.xxx.xxx.xxx...
Connected to your-nginx-webserver-domain.com
.Escape character is '^]'.
HEAD / HTTP/1.0

HTTP/1.1 200 OK
Server: nginx
Date: Fri, 08 Apr 2011 12:04:43 GMT
Content-Type: text/html
Content-Length: 13
Last-Modified: Tue, 22 Mar 2011 15:04:26 GMT
Connection: close
Vary: Accept-Encoding
Expires: Fri, 15 Apr 2011 12:04:43 GMT
Cache-Control: max-age=604800
Accept-Ranges: bytes

The important message in the returned output which confirms your nginx output compression is properly configured is:

Vary: Accept-Encoding

If this message is returned by your nginx server, this means your nginx now will distribute it’s content to it’s clients in compressed format and apart from the browsing boost a lot of server and client bandwitdth will be saved.

Getting around “Secure Connection Failed Peer’s, Certificate has been revoked., (Error code: sec_error_revoked_certificate)

Friday, April 8th, 2011

Certificate has been revoked, sec_error_revoked_certificate screenshot

One of the SSL secured websites (https://) which I have recently accessed couldn’t be opened with an error message showing up:

Secure Connection Failed

An error occurred during a connection to www.domain.com.

Peer’s Certificate has been revoked.

(Error code: sec_error_revoked_certificate)

* The page you are trying to view can not be shown because the authenticity of the received data could not be verified.
* Please contact the web site owners to inform them of this problem. Alternatively, use the command found in the help menu to report this broken site.

That error catched my attention so I digged further in what the message means. Here is what I found as an explanation to what is certificate revocation online

What is a SSL Certificate revocation

Revocation of a certificate means that the Certificate Authority (CA) that issuer of the certificate for a website have decided that the certificate is no longer valid, even if it has not expired.

The information about revocation can be distributed in two ways: Certificate Revocation Lists (CRLs), or by using the Online Certificate Status Protocol (OCSP).

CRLs are (usually) large files that contain a list with information about all the currentely active (unexpired) certificates that are no longer valid. This file has to be downloaded from the CA by the client at regular intervals (usually at least a week apart), and may be quite large.

OCSP, on the other hand, means that the client asks the CA “Is this particular certificate still valid?”, and the server responds “Yes” or “No”. This method can usually be fairly well up to date, meaning the information is at most a few days old, as opposed to at least a week for CRLs.

All the major browsers support OCSP, but some (like Opera) does not currently support CRLs.

By this time most of the modern browsers (Firefox, Chrome, Opera and Internet explorer does support revocation lists and all of the aforementioned hsa enabled at least OCSP by default.

Why SSL revocation error might occur:

A CA can revoke a certificate due to a number of reasons:

– A new certificate has been issued to the website, meaning the old one is not going to be used anymore.
– The website with the certificate is being used for purposes that are not accepted by the CA.
– The certificate was issued based on incorrect information.
– The owner is no longer able to use the private key associated with the certificate, for example the password is lost, the key storage was destroyed somehow, etc.
– The private key has been compromised or stolen, which means traffic to the site is no longer secure.
– The certificate and key have been stolen and is actually being used for fraud while posing as a legitimate website …

Now after all above being said the error:

Secure Connection Failed Peer's, Certificate has been revoked., (Error code: sec_error_revoked_certificate)

is a sure indicator that the website which had the certificate problem as a one you could not trust to make money transactions or do any operation that has a direct relation to your personal private date.

However as there are still websites which use an SSL encryption and are entertainment websites or just a news websites, sometimes getting around the ssl revocation issue to check this website is a necessity.

Therefore to enable your Firefox 3.5 / Iceweasel browser with a website which has ssl certificate revocation issue you need to do the following:

Edit -> Preferences -> Advanced -> Encryption -> Validation

After you see the Certificate Validation screen remove the tick set on:

Use the Online Certificate Status Protocol (OCSP) to confirm the current validity of certificates

Now refresh the website and you will skip the certificate revocation issue error and the webpage will open up.
Note that even though this will work, it’s not recommended to use this work around!