I had some video footage at 4:3 aspect which I wanted to scale and crop to fit a 16:9 wide-screen PAL format. My first attempt was to scale the video to 720×540 (maintaining the 4:3 aspect ratio) and then crop to 720×405 (a 16:9 ratio)
mplayer -vf scale=720:540,crop=720:405 movie.mpg
However PAL has a resolution of 720×576 so I then had to scale the video again
mplayer -vf scale=720:540,crop=720:405,scale=720:576 -aspect 16/9 movie.mpg
What I wanted was to do this in a more simple manner. I realised that I mearly need to scale it to be larger in the first operation, But how much larger? Well since I wanted to crop the same proportion of the image I simply needed to calculate the aspect of the cropped proportion. Which was 540/405 or 4/3 So I actually want my video to be 4/3 taller than its final height. So we want the movie to be 576 × 4/3 = 768
mplayer -vf scale=720:768,crop=720:576 -aspect 16/9 movie.mpg
Here is how one can crudely stream video over the network.
On the server run:
nc -l -p 5500 < video.mpg
And on the client run:
nc 192.168.55.8 5500 | mplayer -cache 8192 -
Human: Ed is a duck.
Computer: Ok ed is a duck.
Human: Ducks can fly.
Computer: Ok ducks can fly.
Human: Can Ed fly?
Human: But Ed is dead.
Computer: Ok Ed is dead.
Human: Can Ed Fly?
Human: Dead things cannot fly.
Computer: Ok dead things cannot fly.
Human: Can Ed fly?
Computers are stupid, they do not have any common sense. You or I would know that ed cannot fly as soon as we were told that ed is dead, but a computer lives in a closed world and as such cannot make any assumptions. This is a good thing because the world would be a very different place if computers did make assumptions. However to make a computer give intelligable answers to questions you need a rules engine.
A Rules engine could consist of a set of processes, i.e a process for each rule that you want to assert to be true. The process could consist of reading some information from a system and then making decisions based on the information. In other words procedural programming.
However, this approach is rather tedious. What you might rather do is describe the set of constraints that must hold true, and have a set of processes generated automatically.
Well that sounds nice, but is it even possible? Well actually yes, and that is what Rules Engines, Constraint based programming 5GL’s are all about.
I wanted to view youtube videos on my phone, but unfortunately the mobile youtube site seems to have less content than the full site. So I decided to make my own mobile phone compatible video files and upload it to my phone. First things first I needed to get the flash video file from the youtube URL, which can be done with this handy site. Next i needed to convert the flash video into a .3gp file that is compatible with my mobile phone. This can be done using ffmpeg (I used a windows version of ffmpeg)
I converted the flash video using the following command.
ffmpeg -i movie.flv -s qcif -r 12 -b 30k
-ar 8000 -ac 1 -ab 12.2k movie.3gp
Finally I copied the files into the video folder on my phone using standard USB Storage Media drivers in windows, which simply present my phone to me as if it were a Hard Drive.
I recently decided to try to transcode an .mp4 (quicktime) movie to burn on to a dvd. Using a windows version of MPlayer and following these instructions I started the transcoding process.
mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd:tsaf
-vf scale=720:432,expand=720:576,harddup -srate 48000 -af
lavcresample=48000 -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:
abitrate=192:aspect=16/9 -ofps 25 -o movie.mpg movie.mp4
This was not the end of the story however. The next step was to convert the output MPG file info a DVD filesystem. This was done using DVDAuthour fortunately version 0.6.9 comes in precompiled windows binaries. The documentation for DVDAuthour was a little flakey however the easiest way was to create the XML file
<video format="pal" aspect="16:9" resolution="720x576"/>
<vob file="movie.mpg" />
And then build the dvd filesystem using
dvdauthor -o ./dvd -x dvdauthour.xml
Finally I have to burn the files to disk using the windows version of growisofs (which requires mkisofs) Using the command
growisofs -dvd-compat -Z e: -dvd-video -V "VIDEO_DVD" ./dvd
I decided to install wordpress. It was surprisingly easy once I had checked that my server supported the requirements, (which was the hardest part) and that I could overlay the WordPress database tables into the wiki database. It was a doddle.
Oh wouldn’t it be nice if propellerheads had more modes for its ECF-42 Filter module.