Posted by gmendoza on December 1, 2009 under Tech Tips | 
When adding third party software repositories to your APT sources list, you can easily download a referenced PGP key to your APT keyring using the advanced options of the apt-key utility.
For example, if you are adding a third party repository that references the PGP key ID of 6E80C6B7, the following will work as long as the key has been uploaded to a keyserver.
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6E80C6B7
gpg: requesting key 6E80C6B7 from hkp server keyserver.ubuntu.com
gpg: key 6E80C6B7: public key "Launchpad PPA for Banshee Team" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
Typically, instructions on adding repositories give readers a two or three step process that involves apt-key reading a key from a text file or piped from a wget command. The above just cuts all that nonsense out.
The apt-key man page is a bit bare, but there are a few other options you might find interesting that are only mentioned in the commands help output.
apt-key
Usage: apt-key [command] [arguments]
Manage apt's list of trusted keys
apt-key add - add the key contained in ('-' for stdin)
apt-key del - remove the key
apt-key export - output the key
apt-key exportall - output all trusted keys
apt-key update - update keys using the keyring package
apt-key net-update - update keys using the network
apt-key list - list keys
apt-key finger - list fingerprints
apt-key adv - pass advanced options to gpg (download key)
Posted by gmendoza 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!
Posted by gmendoza on September 26, 2009 under Tech Tips |
If you have Matroska Video (MKV) files encoded with AC3 Dolby Digital 5.1 or DTS audio tracks, you may want to simply extract the audio, convert it to a 2-channel stereo format like WAV, MP3 OGG, etc, and then add it back into the MKV as a separate audio track. This is useful when your media player (e.g. Western Digital Media Player WDAVN00) will not downscale the audio from a digital format like AC3 or DTS to stereo when you don’t have a receiver or TV with a built in Dolby Digital decoder. Now you’ll have the choice of either audio format depending on your technical requirements.
The great thing about the Matroska multimedia container is that you can easily manipulate these files without having to re-encode, saving lots of time. I’ll be using mkvextract to extract the AC3 audio, ffmpeg to convert ac3 to mp3, and finally mkvmerge to add and remux the new audio track to the MKV container. All of these are available to a number of platforms, but in my examples, I’m using Linux. Check out the MKVToolnix and FFMpeg websites for more info on the software.
If using Ubuntu Linux, install the relevant mkvtoolnix, mkvtoolnix-gui and ffmpeg packages.
sudo apt-get install mkvtoolnix mkvtoolnix-gui ffmpeg libavcodec-unstripped-52
To view the existing tracks of the MKV, use the mkvmerge -i option. In the following example, you see my “Cool.Video.mkv” file has an MPEG4 video in track 1, an AC3 Dolby Digital audio file in track 2, and subtitles in track 3.
mkvmerge -i Cool.Movie.mkv
File 'Cool.Movie.mkv': container: Matroska
Track ID 1: video (V_MPEG4/ISO/AVC)
Track ID 2: audio (A_AC3)
Track ID 3: subtitles (S_TEXT/UTF8)
Using mkvextract, extract the AC3 Dolby Digital audio from track 2, saving it to a file called audio.ac3.
mkvextract tracks Cool.Movie.mkv 2:audio.ac3
Extracting track 2 with the CodecID 'A_AC3' to the file 'audio.ac3'. Container format: Dolby Digital (AC3)
Progress: 100%
ls -lh audio.ac3
-rw-r--r-- 1 gmendoza gmendoza 432M 2009-09-26 11:58 audio.ac3
Convert the 6-channel ac3 file to a 2-channel stereo MP3 using ffmpeg. If you prefer a higher audio bitrate, adjust the -ab value as desired. e.g. 256, 384, etc, and adjust the audio rate to your liking as well.
ffmpeg -i audio.ac3 -acodec libmp3lame -ab 160k -ac 2 audio.mp3
[output omitted for brevity]
ls -lh audio.*
-rw-r--r-- 1 gmendoza gmendoza 432M 2009-09-26 11:58 audio.ac3
-rw-r--r-- 1 gmendoza gmendoza 87M 2009-09-26 12:08 audio.mp3
To simplify things, you could actually skip the digital format extraction process by running ffmpeg against the MKV file directly.
ffmpeg -i Cool.Movie.mkv -acodec libmp3lame -ab 160k -ac 2 audio.mp3
If you prefer encoding with more advanced options, you could extract the audio as a 2-channel WAV file instead, and then process it with LAME, Oggenc, or some other encoder of your choosing. The following shows the extraction to WAV, and then conversion to various formats for fun, e.g. MP3, OGG, and FLAC.
ffmpeg -i Cool.Movie.mkv -acodec pcm_s16le -ac 2 audio.wav
lame -V0 -q0 --vbr-new audio.wav audio.mp3
oggenc -q6 audio.wav
flac audio.wav
Use mkvmerge to combine the original MKV with the MP3 audio track to create a new file called Cool.Movie.New.mkv. Make sure you have enough disk space for both the original and new MKV file.
mkvmerge -o Cool.Movie.New.mkv Cool.Movie.mkv audio.mp3
mkvmerge v2.4.1 ('Use Me') built on Dec 13 2008 21:03:46
'Cool.Movie.mkv': Using the Matroska demultiplexer.
'audio.mp3': Using the MP2/MP3 demultiplexer.
Warning: 'audio.mp3': Skipping 32 bytes at the beginning (no valid MP3 header found).
'Cool.Movie.mkv' track 1: Using the MPEG-4 part 10 (AVC) video output module.
'Cool.Movie.mkv' track 2: Using the AC3 output module.
'Cool.Movie.mkv' track 3: Using the text subtitle output module.
'audio.mp3' track 0: Using the MPEG audio output module.
The file 'Cool.Movie.New.mkv' has been opened for writing.
Progress: 100%
The cue entries (the index) are being written...
Muxing took 270 seconds.
Verify that the audio track has been added. You can see Track ID 4 has been successfully added.
mkvmerge -i New.Cool.Movie.mkv
File 'New.Cool.Movie.mkv': container: Matroska
Track ID 1: video (V_MPEG4/ISO/AVC)
Track ID 2: audio (A_AC3)
Track ID 3: subtitles (S_TEXT/UTF8)
Track ID 4: audio (A_MPEG/L3)
That’s really all there is to it. There are quite a few options available when editing MKV container files. For example, I wanted nice descriptions for my tracks since various media players will read and display them for you during menu navigation. I recommend using the mkvmerge gui application as shown in this screenshot.
It’s really just a front-end application to mkvmerge, and the following text shows the commands that were used to specify the language for each tag, re-order the audio tracks, disable subtitles by default, and give useful descriptions to each Track ID.
mkvmerge -o "Cool.Movie.New.mkv" \
--language 1:eng \
--track-name "1:Cool Movie (MPEG4)" \
--default-track 1:yes \
--display-dimensions 1:40x17 \
--language 2:eng \
--track-name "2:Dolby Digital 5.1 (AC3)" \
--default-track 2:yes \
--language 3:eng \
--track-name "3:English Subtitles" \
--default-track 3:no \
-a 2 -d 1 -s 3 Cool.Movie.mkv \
--language 0:eng \
--track-name "0:2-Channel Stereo (MP3)" \
--default-track 0:no \
-a 0 -D -S audio.mp3 \
--track-order 0:1,0:2,1:0,0:3
mkvmerge -i Cool.Movie.New.mkv
File 'Cool.Movie.New.mkv': container: Matroska
Track ID 1: video (V_MPEG4/ISO/AVC)
Track ID 2: audio (A_AC3)
Track ID 3: audio (A_MPEG/L3)
Track ID 4: subtitles (S_TEXT/UTF8)
Tags: AC3, Audio, Dolby Digital, FFMpeg, LAME, Linux, Matroska, MKV, mplayer, Multimedia, Video
