Posted by admin on November 11, 2009 under Tech Tips | 
If you have a video vile that you wish to convert and burn to DVD, you can do so from a Linux command line very easily. We will use FFmpeg for the video conversion, DVDAuthor to create the DVD file system structure, and Growisofs to burn the DVD.
Using FFmpeg, simply specify your input file, the target format, resolution and an output file name. While the following is an over simplified example, it will more than likely work very nicely in most scenarios. The source video file is movie.avi, the target will be formatted for NTSC, and a standard DVD resolution of 720×480 will be used to create a new video file called movie.mpg. There are many additional options that FFMpeg can use to increase quality, so be sure to check out the documentation.
ffmpeg -i movie.avi -target ntsc-video -s 720x480 movie.mpg
Next, you will need to take your new movie.mpg file, and create a DVD file structure that you will burn to disc. Just create a folder that will serve as the parent directory of your DVD. I Like to name it after the title of the movie. Then you will use dvdauthor to create a title set and table of contents and no DVD menus. The movie will just play. 
mkdir MOVIE_TITLE
dvdauthor -o MOVIE_TITLE/ -t movie.mpg
dvdauthor -o MOVIE_TITLE/ -T
The dvdauthor -t option creates a title track in the VIDEO_TS directory. If you list the contents after running the first command, you’ll see the corresponding VTS_01_0.BUP, VTS_01_0.IFO, and VTS_01_X.VOB files. The -T option creates a table of contents for all title sets in the file system, which are listed as VIDEO_TS.BUP and VIDEO_TS.IFO.
You are now ready to burn the DVD. In the following command, we will use the -Z option to burn an initial session to the disc, the -dvd-video option to generate a DVD-Video compliant UDF file system, and the -V option to give the disc a Volume ID. This Volume ID is read by your computer to and displays as a nice human readable title typically underneath the icon representing the disc. The -dvd-video and -V options are actually part of the mkisofs (genisoimage) command sets, so they do not show up in the growisofs man pages.
growisofs -Z /dev/dvdrw -dvd-video -V MOVIE_TITLE MOVIE_TITLE/
Notice, you do not need to generate an ISO file to burn the DVD. This would only waste space if your intention is not to distribute or store the video as a disc image. To create the image however, that’s as easy as the following.
genisoimage -o MOVIE_TITLE.iso -dvd-video MOVIE_TITLE/
Posted by admin on November 4, 2009 under Tech Tips |
If you ever want to quickly protect a file by encrypting it with a simple password, you can use GnuPG and symmetric key encryption for the job. Using this method, you can use industry strength encryption like AES256 and not have to worry about public and private keys. Just remember your password and use PGP compatible software to decrypt the files when needed.
For example, this is how you can encrypt a zip file called backup.zip and output the result to a new file called backup.zip.gpg.
gpg --symmetric --cipher-algo aes256 -o backup.zip.gpg backup.zip
Enter passphrase: *******
Repeat passphrase: *******
To decrypt the file, the following will work.
gpg -d -o backup.zip backup.zip.gpg
gpg: AES256 encrypted data
Enter passphrase: *******
gpg: encrypted with 1 passphrase
For fun, here’s how to create a Gzip Tar archive (tar.gz) and encrypt it on the fly.
tar czvpf - SomeFiles/ | gpg --symmetric --cipher-algo aes256 -o backup.tar.gz.gpg
Enter passphrase: *******
Repeat passphrase: *******
To decrypt and extract in a single command, the following also works.
gpg -d backup.tar.gz.gpg | tar xzvf -
gpg: AES256 encrypted data
Enter passphrase: *******
gpg: encrypted with 1 passphrase
If you’re curious to know what other ciphers are available to you, simple use the gpg --versioncommand.
gpg --version | grep Cipher
Cipher: 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH
Posted by admin on November 3, 2009 under Tech Tips |
If you want to gain quick insight into the basic properties of a video file from the Linux command line, there’s a few really easy methods. The information you might be interested in are audio and video codecs, resolution, frame rates, bitrates, etc.
Using mplayer, you can see some basic information about a video file. For example, the following video is using the WMV3 video codec at the resolution of 1280×720 (720p), the bitrate of 3000 kbps, etc.
mplayer video.wmv -vo null -ao null -frames 0 2>&1 /dev/null | egrep "(VIDEO|AUDIO)"
VIDEO: [WMV3] 1280x720 24bpp 1000.000 fps 3000.0 kbps (366.2 kbyte/s)
AUDIO: 44100 Hz, 2 ch, s16le, 96.0 kbit/6.80% (ratio: 12003->176400)
The audio rate is shown to be 44100 Hz using 2-Channel stereo, but the codec is not listed. You can get additional information with the -identify option.
mplayer video.wmv -identify -vo null -ao null -frames 0 2>&1 /dev/null | egrep "(^ID|VIDEO|AUDIO)"
ID_AUDIO_ID=1
ID_VIDEO_ID=2
VIDEO: [WMV3] 1280x720 24bpp 1000.000 fps 3000.0 kbps (366.2 kbyte/s)
ID_CLIP_INFO_NAME0=name
ID_CLIP_INFO_VALUE0=
ID_CLIP_INFO_NAME1=author
ID_CLIP_INFO_VALUE1=
ID_CLIP_INFO_NAME2=copyright
ID_CLIP_INFO_VALUE2=
ID_CLIP_INFO_NAME3=comments
ID_CLIP_INFO_VALUE3=
ID_CLIP_INFO_N=4
ID_FILENAME=video.wmv
ID_DEMUXER=asf
ID_VIDEO_FORMAT=WMV3
ID_VIDEO_BITRATE=3000000
ID_VIDEO_WIDTH=1280
ID_VIDEO_HEIGHT=720
ID_VIDEO_FPS=1000.000
ID_VIDEO_ASPECT=1.7778
ID_AUDIO_FORMAT=353
ID_AUDIO_BITRATE=0
ID_AUDIO_RATE=0
ID_AUDIO_NCH=0
ID_LENGTH=2116.00
ID_VIDEO_ASPECT=1.7778
ID_VIDEO_CODEC=wmv9dmo
AUDIO: 44100 Hz, 2 ch, s16le, 96.0 kbit/6.80% (ratio: 12003->176400)
ID_AUDIO_BITRATE=96024
ID_AUDIO_RATE=44100
ID_AUDIO_NCH=2
ID_AUDIO_CODEC=ffwmav2
Another great tool for identifying video attributes is idvid. idvid comes with the tovid package, so be sure to install it from your repository. It is a bit slow, but the output is very clean and easy to interpret.
idvid video.wmv
--------------------------------
idvid
Video identification script
Part of the tovid suite, version 0.31
http://www.tovid.org
--------------------------------
Analyzing file: 'video.wmv'. This may take several minutes...
=========================================================
File: video.wmv
Width: 1280 pixels
Height: 720 pixels
Aspect ratio: 1.77:1
Frames: 63352
Duration: 00:35:13 hours/mins/secs
Framerate: 1000.000 frames per second
Video format: WMV3
Video bitrate: 3000000 bits per second
---------------------------
Audio track 1 (Stream 0.0, AID 0):
---------------------------
Codec: wmav2
Bitrate: 0000 bits per second
Sampling rate: 44100 Hz
=========================================================
Audio is compliant with the following formats:
Not compliant with (S)VCD or DVD
Video is compliant with the following formats:
Not compliant with (S)VCD or DVD
This video does not seem to be compliant with (S)VCD or DVD
standards. If you burn it to a video disc, it may not work.
=========================================================
Finally, another tool that works very well is exiftool. It’s available in the libimage-exiftool-perl package. The output is also very straight forward, and easy to interpret. It’s also a lot faster than idvid because the tool only displays metadata, which in some cases can be misleading.Mplayer and tovid actually probe the video, providing very accurate information at the cost of speed.
exiftool video.wmv
ExifTool Version Number : 7.30
File Name : video.wmv
Directory : .
File Modification Date/Time : 2009:04:20 09:21:58
File Type : WMV
MIME Type : video/x-ms-wmv
File ID : 12341234-1234-1234-1234-123412341234
File Size : 823200182
Creation Date : 2009:03:31 02:52:55Z
Data Packets : 102833
Play Duration : 35:16
Send Duration : 35:13
Preroll : 3000
Flags : 2
Min Packet Size : 8000
Max Packet Size : 8000
Max Bitrate : 3122812
Is VBR : False
Audio Codec Name : Windows Media Audio 9.2
Audio Codec Description : 96 kbps, 44 kHz, stereo 1-pass CBR
Video Codec Name : Windows Media Video 9
Video Codec Description : Professional
Audio Codec ID : Windows Media Audio V2 V7 V8 V9 / DivX audio (WMA) / Alex AC3 Audio
Audio Channels : 2
Audio Sample Rate : 44100
Stream Type : Video
Error Correction Type : No Error Correction
Time Offset : 0 s
Stream Number : 2
Image Width : 1280
Image Height : 720
Title :
Author :
Copyright :
Description :
Rating :
Image Size : 1280x720
As always, comments and additional tips are welcome!
