We made a point-to-point SIP high definition video conference over a local area network. Another test used H.323 protocol. We also included my SIP-enabled Nokia E61i in the conference over the office WiFi network in a direct multipoint call simply calling my phone’s IP address. Crystal clear sound.

The equipment statistics showed the following:
Video

• 1280×720 resolution (720p HD) at 30 frames per second
• H.264 compression
• aprox. 1780 kilobits per second for the compressed video stream

Audio

• AAC-LC compression
• aprox. 70 kilobits per second for the compressed audio stream

Total of aprox. 1850 kbps for excellent and smooth audio and video quality.

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Choosing the file format: .AVI, .OGG, .MP4 or .MKV ?

The ripped video file format is a decision you must make. Currently my format of choice is .MKV or Matroska. I’ll explain why.

It is quite idiotic to say that an .MP4 movie has better quality than a .AVI or vice-verse (or any other combination of comparisons). OGG, MP4 (MPEG-4 Part 14), MKV (Matroska), AVI, WMV (or ASF) are just containers, envelopes. Video quality depends on what goes inside it.

“Multimedia” has this name because you have multiple types of media: video in multiple angles, multiple audio options including different languages and channels (stereo, 5.1, 6 channels etc), subtitles in several languages, chapter information, menu etc. Think about a DVD. So this is a graphical view of how things are organized inside a 900MB movie file in a modern format as MKV or MP4:

A digital multimedia file format must be capable to contain all this different medias and multiplex them in parallel so you won’t have the video in the first 500MB of the file and the audio on the following 500MB (this can’t work for streaming). And this is exactly what modern file formats as MP4 and MKV do: they carry all your movie-related data together.

This is a comparison of all these file formats based on my personal experience with them (a more formal comparison can be found in Wikipedia):

Personally I believe MP4 is the multimedia file format for the future because since it is getting popular, all these unstandardized features will get stabilized. MP4 is an ISO standard and the increasing industry support can be felt on iPods and portable devices, and most notable on home DVD players capable of playing the 700MB MP4 video file burned in a CD.

By the way, remember this:

• MP4 is not an evolution of MP3. AAC (MPEG-4 Part 3) is.
• MP5 and MP6 (used to classify portable media players) are things that simply doesn’t exist in the multimedia scene.
• .M4A, .M4V, .MOV and .3GP files can safely be renamed to .MP4. MP4 is the generic standard name.

Meanwhile, MKV wins everything but on the Industry Support category. But this doesn’t really matter, and I’ll explain why. Since MKV is just a container, the large video, audio etc streams can be extracted and repackaged into MP4 and vice-versa in seconds. No transcoding (decoding followed by an encoding into another format) is needed.

So today I store my videos in the most feature rich and well supported by players format: MKV.

OGG or OGM (the container file format) is practically dead in my opinion. They were created as part of the Xiph initiative for a complete open source patent-free multimedia framework, but seems nobody uses it anymore for video. From the same family, Vorbis (the audio codec compared to MP3, a.k.a. .OGG) is very good but also very not popular. Theora (the video codec) is frequently comparable to old MPEG-1 in terms of quality and compression ration so currently, if you want quality and are not concerned about patents, MPEG-4 AVC is the best choice. FLAC, Xiph’s lossless audio codec, is the winner of the family: very popular, massively used, and recommended.

Encoding the DVD

I use HandBrake, the most practical Open Source (and overall) movie encoder. It runs on Linux, Mac and Windows and uses the same Open Source libraries as ffmpeg, mplayer/mencoder, xine, etc. While these programs are generic video handlers (with thousands of confusing configuration parameters to sustain this generalistic status) HandBrake is optimized only for ripping so it is very easy to use, yet extremely powerful.

#!/bin/bash

##
## This is the script I use to make hifi DVD rips including chapter markers and
## subtitles. It uses Handbrake.
## Contains what I found to be the best quality ripping parameters and
## also let me set simple parameters I need.
##
## Avi Alkalay <avi at unix dot sh>
## http://avi.alkalay.net/2008/03/mpeg4-dvd-rip.html
##
## $Id$
##

#set -vx

HANDBRAKE=${HANDBRAKE:=~/bin/HandBrakeCLI}
#HANDBRAKE=${HANDBRAKE:="/cygdrive/c/Program Files/Handbrake/HandBrakeCLI.exe"}
## Where is the Handrake encoder executable.
## Handbrake is the most practical free, OSS, DVD riper available.
## Download HandBrake for Linux, Mac or Windows at http://HandBrake.fr

INPUT=${INPUT:=/dev/dvd}
## What to process. Can also be a mounted DVD image or simply '/dev/dvd'

TITLE=${TITLE:=L}
## The title number to rip, or empty or "L" to get the longest title

#CHAPTERS=${CHAPTERS:=7}
## Example: 0 or undefined (all chapters), 7 (only chapter 7), 3-6 (chapters 3 to 6)

#VERBOSE=${VERBOSE:="yes"}
## Wether to be verbose while processing.

SIZE=${SIZE:=1200}
## Target file size in MB. The biggest the file size, the best the quality.
## I use to use from 1000MB to 1400MB for astonishing high quality H.264 rips.

OUTPUT=${OUTPUT:="/tmp/output.mkv"}
## Output file. This will also define the file format.
## MKV (Matroska) is currently the best but MP4 is also good.

AUDIO=${AUDIO:="-E ac3 -6 dpl2 -D 1"} # For AC3 passthru (copy).
#AUDIO=${AUDIO:="-E lame -B 160"} # For MP3 reencoding. Good when input is DTS.
## Audio parameters. If input is AC3, use it without transcoding.
## If is DTS, reencode to MP3.

MATRIX=${MATRIX:=`dirname $0`/eqm_avc_hr.cfg}
## x264 matrix to use. The matrix file may increase encoding speed and quality.
## This one is Sharktooth's as found
## at http://forum.doom9.org/showthread.php?t=96298

######### Do not change anything below this line ##############

## Make some calculations regarding title and chapters based on parameters.
SEGMENT=""
if [[ "$TITLE" == "L" || -z "$TITLE" ]]; then
	SEGMENT="-L"
else
	SEGMENT="-t $TITLE"
fi

[[ -n "$CHAPTERS" && "$CHAPTERS" -ne 0 ]] && SEGMENT+=" -c $CHAPTERS"

[[ "$VERBOSE" != "no" ]] && VERB="-v"

# Define args for the x264 encoder. These are some values I found on the net
# which give excelent results.
X264ARGS="ref=3:mixed-refs:bframes=6:b-pyramid=1:bime=1:b-rdo=1:weightb=1"
X264ARGS+=":analyse=all:8x8dct=1:subme=6:me=umh:merange=24:filter=-2,-2"
X264ARGS+=":ref=6:mixed-refs=1:trellis=1:no-fast-pskip=1"
X264ARGS+=":no-dct-decimate=1:direct=auto"
[[ -n "$MATRIX" ]] && X264ARGS+=":cqm=$MATRIX"

# Encode...
"$HANDBRAKE" $VERB -i "$INPUT" -o "$OUTPUT" \
	-S $SIZE \
	-m $SEGMENT \
	$AUDIO \
	-e x264 -2 -T -p \
	-x $X264ARGS

# Repackage to optimize file size, to include seek and to include this
# this script as a way to document the rip...
echo $OUTPUT | grep -qi ".mkv"
if [[ $? && -x `which mkvmerge` && -f $OUTPUT ]]; then
	mv $OUTPUT $OUTPUT.mkv
	mkvmerge -o $OUTPUT $OUTPUT.mkv \
		--attachment-name "The ripping script" \
		--attachment-description "How this movie was created from original DVD" \
		--attachment-mime-type application/x-sh \
		--attach-file $0

	[[ -f $OUTPUT ]] && rm $OUTPUT.mkv
fi

The script seems long because it is fully documented but it actually only collects some parameters and simply runs the HandBrake encoder like this (passed parameters are in red):

~/bin/HandBrakeCLI -v -i /dev/dvd -o /tmp/output.mkv \
    -S 1200 \
    -m -L \
    -E lame -B 160 \
    -e x264 -2 -T -p \
    -x ref=3:mixed-refs:bframes=6:b-pyramid=1:bime=1:b-rdo=1:weightb=1:analyse=all:8x8dct=1:subme=6:me=umh:merange=24:filter=-2,-2:ref=6:mixed-refs=1:trellis=1:no-fast-pskip=1:no-dct-decimate=1:direct=auto:cqm=~/src/randomscripts/videotools/eqm_avc_hr.cfg

All the rest is what I found to be the best encoding parameters.

The resulting video file (/tmp/output.mkv in this case) will contain correctly cropped video and audio quality as good as the DVD (it is almost lossless), and chapter breaks at the same positions read from the DVD.

In a Core Duo machine as my laptop running Fedora 8 or Windows XP, a 2 pass H.264 encoding (2 pass improves quality and H.264 is newer standard MPEG-4 technology better than DivX/Xvid) takes about 4 to 5 hours for a regular 2 hours movie, so leave it encoding while you go to sleep. A Pentium 4 machine running Ubuntu takes about 17 hours for the same rip.

I use to rip one chapter from the movie first (use your preferred video player or lsdvd command to find the shortest chapter), check quality, compare to DVD, fine tune, try again and then shoot full DVD ripping.

After encoding I use to repackage the audio/video stream with Matroska’s mkvmerge (or mmg, its GUI version available on any Linux distribution as “mkvtoolnix” package, and installable for Windows or Mac OS from Matroska’s website) to optimize seeks and to include soft subtitles (that can be turned on and off as on regular DVDs), but I’ll explain that in another HOWTO.

Give Your Ripped Movie a Descriptive File Name

I use to organize my media library in a standard way I invented for myself and which I suggest you to use too.

My movie file names shows everything that the file includes. Some examples:

• Indiana_Jones_and_The_Raiders_of_the_Lost_Ark_IMDB{tt0082971}-Xvid{720×304_23.98fps}+MP3{ENG,POB_VBR}+Sub{ENG,SPA,POB}+Covers.mkv
  
  This is the Indiana Jone’s Raiders of the Lost Ark movie, whose IMDB index is tt0082971 (IMDB{tt0082971}). It was ripped with the old Xvid codec and contains 720×304 pixels frame size at a rate of 23.98 frames per second (Xvid{720×304_23.98fps}). It also contains selectable audio tracks in English and Brazilian Portuguese encoded in variable bit rate MP3 (MP3{ENG,POB_VBR}). In addition, there is also selectable subtitles in English, Spanish and Brazilian Portuguese (Sub{ENG,SPA,POB}). The file also contains the cover images as attachments.
• Harold_and_Maude_IMDB{tt0067185}-H264{672×368_3Pass_25fps}+HEAAC{EN}+Sub{POR,EN,FRE}+Chapters+Covers.mkv
  
  The old Harold and Maude movie whose IMDB index is tt0067185 (IMDB{tt0067185}). It is encoded with H.264 in 3 passes and has 672×368 pixels frame size at a rate of 25 frames per second (H264{672×368_3Pass_25fps}). There is only one English audio track encoded in modern HE-AAC (HEAAC{EN}). Subtitles in Portuguese, English and French (Sub{POR,EN,FRE}), chapter information and attached cover images. This is very complete high quality DVD backup.
• I_Am_Legend_IMDB{tt0480249}-H264{704×304_23.98fps}+AC3{ENG_5.1}+Sub{POR}.mkv
  
  The I Am Legend movie whose IMDB index is tt0480249 (IMDB{tt0480249}), video encoded in H.264 with 704×304 pixels frame size (H264{704×304_23.98fps}), original 5.1 channels AC3 audio in English (AC3{ENG_5.1}) and subtitles in Portuguese (Sub{POR}).

The advantages of this scheme are:

• It is web safe with no spaces in filenames. All underlines. It is also DOS safe.
• To have the IMDB index let me know exactly which movie this file contains. This is particularly good to avoid ambiguity for movies that have remakes as Ben Hur, or movies that have an official name but are well known by other names or have international titles.
• To know the encoding method, subtitles included and chapters info give me the overall quality of the movie right away.
• Special attention to audio and subtitle languages. Having them on the filename let me know I will understand its content without having to play. Sometimes I can’t play the file because I logged in my home computer remotely.

Playing the Ripped File

To play this advanced Matroska media file that contains such a rich set of metainformation and highly compressed digital content you will need an advanced player too. And happens that the best players are the Open Source ones. So use these players:

• On Windows: the k-lite codec pack with the Media Player Classic (which is better than Microsoft’s Windows Media Player)
• On Linux: use MPlayer or Xine (or variants as Kaffeine, GMPlayer, KPlayer, KMPlayer) available from your Linux distribution’s package repositories. For example, see the instructions to get them on a Fedora installation.
• On Mac: use VLC Media Player.

These are Media Player Classic screenshots demonstrating how to activate the advanced content inside a Matroska file. Players on other platforms have similar capabilities and menus.

Activating embedded subtitles and languages
The player lets you choose the audio language and subtitles. On MPC for example, this is how you turn on and off and choose the language for subtitles.

As you can see, the player found subtitles embedded in the MKV file in English, Hebrew and Portuguese.

If the MKV file contains many audio tracks (as different languages, director’s comments etc) this is how to select it:

And to jump directly to a specific chapter on the movie, if the MKV file contains this kind of information:

Improving audio volume
If you ripped the movie without reencoding the audio, the final file will contain DVD’s original AC3 audio tracks in 6 channels (5+1). This may sound with a lower volume when played in a 2-speaker system as your laptop, iPod, etc because 4 channels are simply not being played. To remediate this the player will have to downsample the audio. In other words, it will remix the 6 channels into 2 stereo channels while playing. The Media Player Classic options should look like this:

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Adobe’s press release says it all: lab version of o Flash Player 9.0 supports latest and best multimedia technologies.

Thanks to YouTube and other online video services, the Adobe Flash Player browser plug in is probably the most popular video player in the world. But before this version, only the proprietary and now inefficient FLV format was supported.

Tinic Uro, a multimedia software engineer at Adobe explains that the Player now supports:

• H.264/MPEG-4 AVC
  The best, most sofisticated and advanced video codec, capable of high quality, low bitrate video performances. H.264 is the standard for HD-TV, HD-DVD and BluRay. H.264 is better than MPEG-4 ASP/Xvid/DivX.
• AAC and HE-AAC (a.k.a AAC SBR)
  The ISO successor of MP3, for audio. MP3 is already very good, extremely popular, and still supported by the MPEG-4 ISO standard and Flash Player. There is no practical advantage on AAC over MP3 for the music you load in your portable player, but HE-AAC achieves much better quality on very low bit rates (desired for streaming) than MP3.
• MP4 file format
  The MP4 container was designed for many types of usages, including streaming over the Internet. An MP4 file can carry many video, audio, subtitle, scripting, VRML, XML and other metadata multiplexed and in parallel.

All this formats are parts of the ISO MPEG-4 standard.

This is a much expected update for the Flash Player and its users. Every new video on YouTube is being compressed with this technologies since June and the old ones will be converted over time.

We will see quality and speed improvements in multimedia content happening in the right way. Also, the formats of the video files people exchange will converge into a single one based on MPEG-4 standards: MP4 files containing higher-quality-for-megabyte H.264, AAC and subtitle streams.

This is also good news for the Linux and open community. A number of good MPEG-4 related authoring tools already exist and are maturing fast: x264 for video compression, FAAD/FAAC for audio, and GPAC and others for MP4.

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The Nokia E Series smartphones are currently the most advanced in the market. Some may say iPhone but there is no more than great usability and fancy-ness on it.

These are a few characteristics I like in E61i:

1. QWERTY keyboard. I’m tired of loosing stylus pens and even use them to point things.
2. WiFi with power save features. This is unique and as far as I know only Nokia and now the iPhone have it. E61i can also connect to Cisco WiFi networks with LEAP authentication, as used by my company. At work, at home and everywhere it finds a WiFi network I stay connected all the time with a sort of smart roaming, without running out of batteries.
3. A wide screen and great web features as integrated feed reader and full XHTML browser based on KDE’s Konqueror that perfectly render very well all pages I need.
4. Integrated Java support so I can install a practical mobile Google Maps application amongst others.
5. Media features as MP3, MPEG-4’s AAC, MPEG-4 video (low profile DivX/Xvid) and MP4 container support.
6. 2 megapixel camera for pictures and video.
7. Can syncronize PIM data with anything that supports the SyncML Open Standard, for example the ScheduleWorld.com service.
8. Has Text To Speech capabilities, so everytime somebody calls me, the phone actually speaks his or her name as it is written in the contacts database. There are options to install and use different voices and language accents.
9. Has voice recognition capabilities, so I can press a button in the wireless bluetooth phones to make the phone as for a name, I speak it and it recognizes by how it is written in the contacts database. I did not have to record each contact’s name as previous phone models. Nokia E61i actually recognizes what I speak.
10. And, to keep me hacking, the most important: integrated VoIP support through the SIP standard.

This last point deserves an explanation. To use VoIP you usually have to install a softphone in your computer and be close to it to make calls. Well, this phone kind of has a standards compliant softphone already installed in the OS. Together with great WiFi support, I can carry my work extension and other SIP accounts with me all the time, to make cheap international calls and also receive free calls.

This is all very geeky and I love it.

In further articles I’ll explain how to configure advanced features I’ve been using in my new Nokia E61i, a very portable computer.

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Inspired by an old post by Rui Moura, I’ll maintain here the plain commands needed to setup a freshly installed Fedora or Red Hat system, to include essential softwares they don’t ship by default due to legal issues.

These instructions are currently optimized for Fedora 8, but most of it works for Fedora 7 and modern Red Hat Enterprise Linux too. Good suggestions provided as comments bellow will be added to this guide.

Terms highlighted in red should be changed to match your system.

Permissions Setup

This step will allow you to issue some administrative commands without having to be all the time logged in as root — the system administrator.

bash# echo 'your_plain_loginname_here ALL=(ALL) ALL' >> /etc/sudoers

Note that this is the only command throughout this guide that shows a root prompt (bash#). All other commands are indicated to be run as a regular non-root user (indicated by bash$).

After configuring sudo, every time you execute an administrative command with its help, a password is requested. This is your password (the regular user’s password), not the root password.

Keeping System Updated

After all the steps bellow and from time to time, update all software installed on your system with the following command:

bash$ sudo yum update

Repositories Setup

Livna and FreshRPMs are repositories of many essential multimedia and general purpose software for Fedora and Red Hat systems.

bash$ sudo rpm -Uvh http://rpm.livna.org/livna-release-8.rpm

Install Adobe Flash Player Globally

bash$ sudo rpm -Uvh http://linuxdownload.adobe.com/adobe-release/adobe-release-i386-1.0-1.noarch.rpm
bash$ sudo yum -y install flash-plugin

Restart your browser to activate the plugin.
For reference: Flash Player for Linux home page.

Access LAN Hosts by Name Without a DNS Server

You can access servers and machines on you LAN by name, instead of using their long IP address using the Zeroconf standard (implemented as Avahi in Linux). This is so useful and works out of the box in Ubuntu. The setup in Fedora is easy too, but not automatic.

bash$ sudo yum -y install avahi-tools nss-mdns

Now, instead of accessing local hosts by their IP, you can use the .local domain appended to their names. Just like this:

bash$ ssh 10.0.0.5 # stop using the IP address of dbserver
bash$ ssh dbserver.local # start using its hostname

Tip grabbed from Fedora Project wiki.

Keep Date and Time Correct and Precise

Your system can have 100% correct time and date everyday, synchronizing with atomic clocks across the Internet.

bash$ sudo yum -y install ntp    # install time sync tools
bash# ntpdate 0.fedora.pool.ntp.org    # make the first time sync with a Fedora clock mirror
bash# chkconfig --level 2345 ntpd on    # enable the synchronization service to run on every boot
bash# service ntpd start    # run the service so you don't need to reboot

Read more in the official Linux Time Precision HOWTO.

Dramatically Improve Fonts

bash$ sudo yum install freetype-freeworld

Logoff and login again your graphical environment to this update take effect.

To understand why you need this update read this section on the Linux Font HOWTO.

The freetype-freeworld package uses a technique described in this bug report.

Install Web Standard Fonts

These packages include popular fonts as Arial, Times New Roman, Tahoma, Verdana, as well as new Windows Vista and MS Office 2007 fonts. Learn more.

bash$ sudo rpm -Uvh \
http://avi.alkalay.net/software/webcore-fonts/webcore-fonts-3.0-1.noarch.rpm \
http://avi.alkalay.net/software/webcore-fonts/webcore-fonts-vista-3.0-1.noarch.rpm

Then, configure your desktop as described in the Linux Font HOWTO, for KDE or Gnome.

MP3 Support

For Gnome and GStreamer:

bash$ sudo yum -y install gstreamer-plugins-ugly libmad libid3tag id3v2

For KDE:

bash$ sudo yum -y install kdemultimedia-extras-nonfree id3v2

Amarok: The best audio player for Linux

bash$ sudo yum -y install amarok-extras-nonfree

DVD Player

bash$ sudo yum -y install vlc

General DVD and Movie Player and Browser Plugin

bash$ sudo yum -y install mplayer mplayer-fonts mplayerplug-in

General Digital Video Authoring and Editing tools

bash$ sudo yum -y install mencoder mkvtoolnix mkvtoolnix-gui ffmpeg avidemux

Correctly install Java

Fedora 8 includes what will be the new Sun Java 1.7 JVM that was open sourced in late 2006.

This JVM (codename Iced Tea) is still beta and may not fulfill all your needs, but it is now extremely easy to install:

bash$ sudo yum -y install java-1.7.0-icedtea    # installs the JRE only

Other subpackages you can install with similar command are java-1.7.0-icedtea-devel (JDK), java-1.7.0-icedtea-plugin (browser plugin), java-1.7.0-icedtea-demo, java-1.7.0-icedtea-src, java-1.7.0-icedtea-javadoc.

If the 1.7 does not fulfill your needs, I wrote another similar tutorial on how to correctly install traditional Java that will become obsolete as soon the Iced Tea project is final, but may be enlightening about how to install other Java related libraries and packages.

Access Windows NTFS Partitions From Linux

bash$ sudo yum -y install ntfs-config

Then run the ntfs-config-root graphical tool and configure your partitions to be writable and mountable.

bash$ sudo /usr/sbin/ntfs-config-root

An example of my system:

After you configure the tool and quit, your NTFS partitions will be mounted in the specified place. In my case /media/Windows and /media/Work.

Configure text console in high resolution and smaller fonts

This tip is for the text console.

bash$ sudo echo 'SYSFONT="lat0-08"' >> /etc/sysconfig/i18n  # set a ISO-8859-15 font
bash$ sudo echo 'fbset 1024x768-60' >> /etc/rc.d/rc.local    # set console resolution to 1024x768 @ 60Hz

These settings will take effect after a reboot, but you can test them before rebooting executing the following commands:

bash$ sudo setfont lat0-08
bash$ sudo fbset 1024x768-60

Note that you can set different resolutions than 1024×768 if you have a video card and monitor that will accept it. A full list of modes can be listed with the command:

bash$ grep "mode " /etc/fb.modes

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Em seu site há 3 lindos videos mostrando a operação fácil do aparelho. Mas exige Quicktime e sem isso não funciona. Para um leigo.

Mas como já sabia que a Apple usa padrões ISO em seus videos, tipo MP4, H.264 e AAC, foi só ver o fonte e descobrir a URL dos videos. Então é só clicar com o botão direito, salvar o arquivo MOV (MP4) e depois assistir com MPlayer ou outro player de Linux que você preferir.

Never been an iPod

How to

Calamari

Ou então, se tiver um link rápido, pode assistir enquanto baixa, assim:

bash$ mplayer http://movies.apple.com/movies/us/apple/iphone/never_been/apple-iphone-never_been_848x496.mov
bash$ mplayer http://movies.apple.com/movies/us/apple/iphone/how_to/apple-iphone-how_to_848x496.mov
bash$ mplayer http://movies.apple.com/movies/us/apple/iphone/calamari/apple-iphone-calamari_848x496.mov

Os links que escolhi são os de alta definição. Há versões com qualidade mais baixa no site original.

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Mas não o culpe por isso. Linux só foi a base tecnológica para todo o sistema.
Ontem conversei bastante com o pessoal da Engebras, empresa que cria e administra a maioria dos radares de São Paulo e outros estados. Já tinha ouvido falar que todos os sistemas para suportar essa monitoração era baseada em Linux, e eles contaram mais detalhes. Continue lendo…

Os radares são na verdade câmeras analógicas com sensibilidade melhorada conectadas a computadores próximos que rodam Linux que por sua vez digitalizam a imagem instantaneamente com a ajuda de placas de captura de vídeo. As placas dos carros são imediatamente reconhecidas por OCR por uma biblioteca de uma empresa israelense, a multa é impressa, enviada pelo correio, recolhida no banco e repassada para o governo estadual, federal ou município, dependendo da jurisdição.

Todos os carros que passam por um radar — infrator ou não — são filmados. Não é uma câmera fotográfica, e sim uma filmadora.

Tazo (gerente de informática da Engebras) e seu pessoal afirmaram que todos os sevidores da empresa rodam Linux. Coisa de 50 a 60 servidores. Mas são servidores paravirtuais. Porque servidores físicos mesmo a empresa tem menos de 10.

Fiquei feliz em ver um exemplo vivo de um datacenter inteiramente virtual, e imaginei a flexibilidade operacional que eles tem em fazer movimentações de serviços sem indisponibilidades.

Mostraram sua extranet onde pode-se ver as fotos de infrações do momento, mais estatísticas de variação de velocidade média por hora, número de veículos, e até seu tamanho. Mostraram também como motoqueiros cometem infrações, mas escondem sua placa com a mão.

Além disso, imediatamente consultam uma base de dados de veículos não licenciados (em MySQL), mas aqui não se pode multar por radar. Por outro lado uma aviso é enviado para a polícia da região, avisando a placa e o ponto onde o veículo foi detectado.

40% da frota nacional não é licenciada, inclusive viaturas da polícia.

Há também os radares de farol, onde não basta uma imagem estática. É necessário registrar o movimento do veículo ultrapassando o sinal vermelho como evidência. Neste caso são usados softwares livres como ffmpeg para gerar este clip em MPEG.

A comunicação entre os radares e o datacenter central é geralmente provida por GPRS, pelas operadoras de celular da localidade.

Se tiver sorte, o pessoal da Engebras vai passar no meu blog para dar mais detalhes de sua operação.

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DivX e Xvid são compressores ainda bons mas de gerações anteriores. O mais moderno e avançado é o H.264 também conhecido por MPEG-4 AVC, padrão ISO. Uma das melhores implementações desse compressor é livre: o projeto x264.

E sobre containers, um dos mais completos hoje em dia é o MP4. Um mesmo arquivo MP4 pode conter uma trilha de vídeo, outra de vídeo em outros ângulos, outra de audio em inglês, outra de audio em português, e outras de legendas em várias linguas, em Unicode, menu como o de um DVD, informação sobre capítulos etc. Isso é um significativo avanço em relação ao container AVI da Microsoft que não suportava nada disso. Pode-se fazer um backup de um DVD para um arquivo MP4, incluindo toda a sua interatividade, menus e capítulos.

Apesar do nome sugestivo, MP4 não é a evolução do MP3. Afirmar isso é como dizer que .gif evoluiu para .tar, coisa que não faz sentido. A evolução do MP3 é AAC e HE-AAC. MP4 (um formato de container) pode conter streams MP3 (um formato de audio), como fiz abaixo, mas o mais natural e moderno é um MP4 conter streams AAC.

Converti um vídeo de 53 segundos que fiz com minha câmera. Veja a comparação:

Há duas discrepâncias aqui:

1. O tamanho relativo do container deveria ter diminuido.
   O overhead do container MP4 é bem menor que AVI, mas como o tamanho do vídeo diminuiu muitíssimo, isso distorceu a relação do tamanho do container com o do arquivo. Se transferíssemos sem recomprimir os streams de audio e vídeo do AVI p/ MP4, veríamos uma significativa queda de overhead do container.
2. O tamanho da trilha de audio aumentou.
   O fato é que tive sérios problemas para compactar o audio. Minha câmera grava som em formatos tão baixos que tive que aumentar a freqüência do sinal para o arquivo ser aceito pelo LAME. E ai usei bitrates talvez altos de mais para a compressão. Mas ganhei tanto com o H.264 que nem vou esquentar a cabeça.

O vídeo final é de alta qualidade (comparado com o original), e não consegui perceber diferença entre eles. Olhei várias vezes, com muita atenção.

Eu ainda fiz questão de alta qualidade, e mantive o bitrate em 2495 kbps. Poderia ter diminuido mais ainda o tamanho se fizesse compressão em 2 passos. Filmes em formato Xvid (MPEG-4 ASP) que se baixa da Internet, em boa qualidade, tem aproximadamente 850 kbps. É esperado que se dermos só 850 kbits para o H.264 trabalhar 1 segundo de vídeo, obteremos resultados melhores comparados ao Xvid.

© Avi for Avi Alkalay, 2007. | Permalink | 9 comments | Add to del.icio.us
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Um podcast é um blog não-textual. Seu conteúdo pode ser audio e/ou vídeo, rodeado por metainformações do tipo “autor”, “entrevistado”, “banda”, “estilo”, “sumário” etc.

Como todo blog, ele tem regularidade: “episódios” no lugar de posts e assim por diante.

Você “assina” um podcast como assina uma revista, da mesma forma como assina um blog (via RSS ou ATOM). Mas como um browser é um leitor essencialmente textual, é mais comum e prático assinar podcasts usando softwares de mídia: iTunes, Yahoo! Music Engine, Amarok, etc.

Na convergência das coisas, um podcast pode ser comparado a um programa de rádio onde o próprio ouvinte decide quando e como vai ouvi-lo.

Num mundo onde tivermos banda larga no ar tão abundante e livre quanto ondas de rádio, além da memória para freqüências de estações, os rádios de nossos carros terão também a assinatura de nossos podcasts preferidos. Com ainda não chegamos a isso, temos que usar MP3 players modernos como o iPod - que tratam podcasts de forma especial - para termos essa funcionalidade.

E nesse mundo, os podcasters seremos você e eu, pessoas comuns falando diretamente para o mundo. Publicar um podcast é tão simples quanto publicar posts num blog. É inclusive algo que se pode integrar com plataformas de blogs comuns, com plugins para Wordpress, etc.

Se você tem um fluxo de coisas para dizer, crie um podcast. Se você tem um fluxo de coisas para serem assistidas, crie um podcast. Se você tem um fluxo de coisas que quer que as pessoas ouçam, crie um podcast. Este último é o meu caso, sobre Jazz Brasileiro, e por isso estou juntando os pedaços e os módulos para criar um.

Andei estudando isso ultimamente, e achei importante compartilhar…

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First make sure you have ffmpeg (video encoding and decoding tools) and lame (MP3 audio encoding and decoding tools) softwares and dependencies installed on your system. You will also require the youtube-dl scripts that downloads the actual YouTube video.

In a Red Hat or Fedora system you can install it from Dag or Livna RPM repositories, with a simple yum command:

bash# yum install ffmpeg lame youtube-dl

Then you get to the YouTube video page you want to download. In this example we’ll use the Heist video, the first Linux ad from IBM, that has http://www.youtube.com/watch?v=DO9ZWDaLLxA as its URL.

I’ll use youtube-dl this way:

bash$ youtube-dl -t http://www.youtube.com/watch?v=DO9ZWDaLLxA

And I saw it connecting to YouTube several times and downloading the video. In the end, I found a big file named the_heist-RRZyz1vXkPE.flv in the current firectory, which is the video file.

Now lets convert it into MPEG with ffmpeg:

bash$ ffmpeg -i the_heist-RRZyz1vXkPE.flv -acodec copy -sameq heist.mpg

-acodec copy will cause ffmpeg to copy the audio from input to output file, while -sameq causes the output video quality to be the same as the source, but output file will be very big. For YouTube videos, you can use -b 320000 instead of -sameq to get smaller file sizes.

I saw ffmpeg taking some time to convert, and in the end I got the heist.mpg file which I was able to confortablly play in any MPEG aware video player, as mplayer.

If you want to convert the video file into MP4, which is the format supported by iPod Video players, you just change the extension:

bash$ ffmpeg -i the_heist-RRZyz1vXkPE.flv -acodec copy -b 320000 heist.mp4

Ffmpeg will take care to use the maximum screen size available from the source (the .flv file) so the converted file will be as hi-fi as YouTube let be (not too high really).

Enjoy your video.

© Avi for Avi Alkalay, 2006. | Permalink | 9 comments | Add to del.icio.us
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