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Posts Tagged ‘convert’

convert mp4 to webm and ogv

November 5, 2016 Leave a comment

Problem
I wanted to share an .mp4 file on my webserver but Firefox didn’t play it. It turned out Firefox prefers the .webm and .ogv formats, while Chrome can play .mp4.

Solution

Convert mp4 then:

.mp4 to .webm

ffmpeg -i input.mp4 -vcodec libvpx -acodec libvorbis -b:v 600k -cpu-used 4 -threads 8 output.webm

To change the quality, play with the “600k” value (bitrate).

.mp4 to .ogv

ffmpeg -i final.mp4 -vcodec libtheora -acodec libvorbis -b:v 600k -cpu-used 4 -threads 8 final.ogv

Here the difference is the codec (libtheora instead of libvpx).

Maybe I missed something, but the .webm file seemed to me to have better quality than .ogv. So I think it’s enough to support two formats only: .mp4 for Chrome and .webm for Firefox. By the way, in my test the input file (.mp4) had the best quality and smallest filesize, but again, I may miss something.

And here is an HTML5 code that can play your video:

<video controls preload="metadata" width="1024" height="768" poster="images/front.jpg">
    <source src="video.mp4" type="video/mp4">
    <source src="video.webm" type="video/webm">
    <p>Please use a modern browser to view this video.</p>
</video>
Categories: firefox Tags: , , , , , ,

convert a LibreOffice Calc/Excel stylesheet to .csv in command-line

November 21, 2015 Leave a comment

Problem
I have a stylesheet made with LibreOffice Calc / Excel. The extension of the file is .ods or .xls / .xlsx. How to convert it to .csv? From the command line, of course.

Solution
Convert an .ods file:

libreoffice --headless --convert-to csv file.ods

Convert an Excel file:

libreoffice --headless --convert-to csv file.xlsx

Tip from here.

If you use --convert-to html, then you get an HTML output.

Categories: bash Tags: , , ,

taking a screenshot about a webpage

July 11, 2015 Leave a comment

Problem

You know the URL of a webpage and you want to take a screenshot of it. For instance you want a thumbnail about the webpage.

Solution

It can be done very nicely with PhantomJS.

What is PhantomJS?
PhantomJS is a headless WebKit scriptable with a JavaScript API. It has fast and native support for various web standards: DOM handling, CSS selector, JSON, Canvas, and SVG.” (source)

How to install PhantomJS?
Follow the instructions here. Under Ubuntu I compiled it from source to get the latest version. Note that it takes a lot of time (about 30 minutes). Under Manjaro I could install it via yaourt and it took 1 minute (and got the newest version). The good news is that installation is not a problem.

How to take a screenshot?
If you download the source, you get a lot of example scripts. One of them is called rasterize.js, and this is exactly what we need.

$ phantomjs rasterize.js 
Usage: rasterize.js URL filename [paperwidth*paperheight|paperformat] [zoom]
  paper (pdf output) examples: "5in*7.5in", "10cm*20cm", "A4", "Letter"
  image (png/jpg output) examples: "1920px" entire page, window width 1920px
                                   "800px*600px" window, clipped to 800x600

Example #1:

phantomjs rasterize.js http://raphaeljs.com/polar-clock.html clock.png


Example #2:

phantomjs rasterize.js https://www.reddit.com/ red.png

It produced an image with dimension 600×3304. It’s too narrow, let’s fix that.

Example #3:

phantomjs rasterize.js https://www.reddit.com/ red.png 1024px

Its dimension is 1024×2432. Looks much better.

Example #4:
The previous image was too high. Let’s take a photo of that part that would be visible on our screen. For this we need to clip a window.

phantomjs rasterize.js https://www.reddit.com/ red.png "1024px*768px"

Great. Now scale it down to get a thumbnail.

Scaling down an image to thumbnail size

$ phantomjs rasterize.js https://www.reddit.com/ screenshot.png "1024px*768px"
$ convert -resize 250 screenshot.png thumb.jpg

The command convert comes from the ImageMagick package. Here we resize the image to width 250px. Convert will keep the image ratio, i.e. it figures out the height value.

Links

convert .wmv to .mp4

ffmpeg -i input.wmv -c:v libx264 -crf 23 -profile:v high -r 30 -c:a libfaac -q:a 100 -ar 48000 output.mp4

More info here.

Categories: bash Tags: , , , ,

resize an image to a given width by keeping the aspect ratio

Problem
You want to resize an image to a given width but you want to keep the width/height ratio of the image.

Solution

convert -resize 200 big.jpg small.jpg

Here the new width will be 200 pixels.

Categories: bash Tags: , ,

convert .txt to .pdf

December 15, 2014 Leave a comment
pandoc input.txt -o output.pdf

By the way, pandoc can convert from / to lots of file formats.

Categories: bash Tags: , ,

animated GIFs

September 3, 2013 Leave a comment

Extract images from a GIF:

convert animated.gif frames%03d.png 

More info here.

Merge images into an animated GIF:

convert -delay 20 -loop 0 *.png result.gif

More info here.

Categories: bash Tags: , ,