Tag Archives: Computing

An FFMPEG Question – Why PHP’s exec() Doesn’t Return the Command Output

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string exec (…)

Here’s the tricky part. As we know from the exec() man page this function executes the given command. As described there, the exact declaration of this method is:

string exec  ( string $command  [, array &$output  [, int &$return_var  ]] )

So far so good. Normally exec() will return the output of the command.

FFmpeg version SVN-r21880, Copyright (c) 2000-2010 Fabrice Bellard, et al.
  built on Feb 18 2010 15:53:28 with gcc 4.3.2
  configuration: --enable-gpl --enable-nonfree --enable-shared --enable-postproc --enable-avfilter --enable-avfilter-lavf --enable-pthreads --enable-x11grab --enable-bzlib --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-version3 --enable-libdc1394 --enable-libfaac --enable-libfaad --enable-libfaadbin --enable-libgsm --enable-libmp3lame --enable-libschroedinger --enable-libtheora --enable-libvorbis --enable-libx264 --enable-libxvid --enable-zlib --prefix=/usr/local
  libavutil     50. 9. 0 / 50. 9. 0
  libavcodec    52.54. 0 / 52.54. 0
  libavformat   52.52. 0 / 52.52. 0
  libavdevice   52. 2. 0 / 52. 2. 0
  libavfilter    1.17. 0 /  1.17. 0
  libswscale     0.10. 0 /  0.10. 0
  libpostproc   51. 2. 0 / 51. 2. 0
...

However sometimes that is not so true. Let’s see an example with the popular FFMPEG program. In one hand when you try to start a video converting program with PHP you can simply call exec with the FFMPEG command as the first parameter. The output is OK and you can dump it as in the example here.

echo exec('/usr/local/bin/ffmpeg -i input.mp4 -acodec libfaac -ab 128k -ac 2 -vcodec libx264 -vpre normal -threads 0 output.mp4', $output);	
var_dump($output);

In some cases you can call FFMPEG only with the -i option to get some info about the input file. Such info can be the size of the image, the bitrate of the source file or the length of the movie. Executing this command:

echo exec('/usr/local/bin/ffmpeg -i input.mp4', $output);	
var_dump($output);

in the terminal you’ll see the output you wish. However if you trying to execute the command via exec() the output remains empty?

Why the Output Parameter is Empty?

Looking at the terminal screen you can’t see the difference, but actually in the second case, when you execute FFMPEG only with the -i option, the output is redirected to the standard error output. That’s why you can’t see it in the exec() second parameter. However there is a solution.

Sometimes PHP's exec() doesn't return the command output. You've to be sure that the command output is not redirected to the standard error stream.
Sometimes PHP's exec() doesn't return the command output. You've to be sure that the command output is not redirected to the standard error stream.

Solution and Conclusion

The solution is quite simple. You’ve to redirect the output of the FFMPEG command to the standard output.

/usr/local/bin/ffmpeg -i /var/www/android/test.mp4 2>&1

Now you can call this line with exec().

echo exec('/usr/local/bin/ffmpeg -i input.mp4 2>&1', $output);	
var_dump($output);

This showcase with the FFMPEG is important not only because now you can call FFMPEG’s command without problems, but because you now know that exec() can’t read the standard error output. Thus you’ve to be careful and always redirect to the standard output.

Use fopen() to Check File Availability?

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Zend Framework and Zend_Http_Client

PHP's fopen() can be used to check remote file existence
PHP's fopen() can be used to check remote file existence

I’ve posted about Zend_Http_Client. Simply there you can ‘make’ your own http client and you can request a remote file. Just to check what’s going on with this file.

// new HTTP request to a file
$httpClient = new Zend_Http_Client('http://www.example.com/myfile.mp4');
 
// get the HEAD of the response and match agains the
// Content-Length. That's because using the Content-Type is slower
$response = $httpClient->request(Zend_Http_Client::HEAD);
 
// if the Content-Length is 0 the file doesn't exists
if (0 === (int)$response->getHeader('Content-Length')) {
	echo 'the file doesn\'t exits';
}

However is there any other way to answer the same question?

fopen()

Yes and no? Perhaps yes, but you should be careful. I’m still not sure it can be used in any case. However here’s the snippet.

if (FALSE === @fopen('http://www.example.com/myfile.mp4', 'r')) {
	echo 'the file doesn\'t exists';
}

fopen() will return FALSE whenever the file doesn’t exists.

In both cases I request a remote file – an MPEG-4 file. Note that fopen()’s first parameter can be a HTTP resource.

jQuery.unbind()

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Binding Problems

jQuery JavaScript Library
jQuery JavaScript Library

Typically in jQuery when you bind an HTML element with some event this event is fired every time the user (client) triggers it. Thus when you’ve a click event attached on a button you can click it as many times as you want. In some rare cases this can be tricky. Let’s imagine the following scenario.

  1. The user clicks on a “vote” button.
  2. Some AJAX calls are performed.
  3. After a successful AJAX call you setup a cookie to deny further votes from this machine.

This seems to be pretty well known scenario, but as the click event is attached to the button there is enough time to click several times on the “vote” button and to vote several times. In this case before the cookie is set the user can vote more than once. Continue reading jQuery.unbind() →

How to Collect the Images and Meta Tags from a Webpage with PHP

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Meta Tags and the Facebook Example

You’ve definitely seen the “share a link” screen in Facebook. When you paste a link into the box (fig. 1) and press the “Attach” button you’ll get the prompted cite parsed with a title, description and possibly thumb (fig. 2). This functionality is well known in Facebook, but it appears to be well known also in various social services. In fact Linkedin, Reddit, Dzone‘s bookmarklet use it.

Facebook Attach a Link Prompt Screen
fig. 1 - Facebook Attach a Link Prompt Screen

Fist thing to notice is that this information, prompted by Facebook, is the same as the meta tag information. However there is a slight difference.

Facebook Attached Link Screen
fig. 2 - Facebook Attached Link Screen

Facebook prefers for the thumb the image set into the <meta property=”og:image” … />. In the case above this tag appears to be:

<meta property="og:image" content="http://b.vimeocdn.com/ts/572/975/57297584_200.jpg" />

And the image pointed in the SRC attribute is exactly the same as the one prompted by Facebook (fig. 3).

Vimeo Thumb
fig. 3 - Vimeo Thumb

First thing to note is that the real thumb is bigger than the thumb shown in Facebook, so Facebook resizes it and the second thing to note is that there are more meta tags of the og:… format. Continue reading How to Collect the Images and Meta Tags from a Webpage with PHP →

Adding a Custom Button to TinyMCE – REVISED

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Driven by the comment of Afraithe I have to apologize about the yesterday’s post. Here’s a much much simpler, cleaner way do add a custom button to TinyMCE.

<script type="text/javascript" src="<your installation path>/tiny_mce/tiny_mce.js"></script>
<script type="text/javascript">
tinyMCE.init({
    mode : "textareas",
    theme : "advanced",
    theme_advanced_buttons1 : "mybutton,bold,italic,underline,separator,strikethrough,justifyleft,justifycenter,justifyright, justifyfull,bullist,numlist,undo,redo,link,unlink",
    theme_advanced_buttons2 : "",
    theme_advanced_buttons3 : "",
    theme_advanced_toolbar_location : "top",
    theme_advanced_toolbar_align : "left",
    theme_advanced_statusbar_location : "bottom",
    plugins : 'inlinepopups',
    setup : function(ed) {
        // Add a custom button
        ed.addButton('mybutton', {
            title : 'My button',
            image : 'img/example.gif',
            onclick : function() {
                // Add you own code to execute something on click
                ed.focus();
                ed.selection.setContent('Hello world!');
            }
        });
    }
});
</script>
 
<form method="post" action="somepage">
        <textarea name="content" style="width:100%">
        </textarea>
</form>

The Problem

There is only one problem – I still cannot find easily the section of the site in TinyMCE. So I’m supposed to click on the comment’s link. This is a pity and perhaps that’s why I couldn’t find it before. Moxiecode should make this section more accessible!