Internetes médiakommunikáció
Fájlformátumok és kodekek
Takács György
8. előadás
2009. 04. 29.
T.Gy. Intrernetes
médiakommunikáció. 2009.04. 29.
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Fontos cél a kérdőív alapján!
Hogyan csináljunk internetes műsorszórást!
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Hang és videó elérése a HTTP használatával
• A HTTP lényegében egy fájl visszanyerési
protokoll
• Teljes fájlt kell letölteni a TCP miatt
• Fájlformátumokat eleinte a helyi hozzáférésre
tervezték
– nagy fájlméretek
– letöltés közbeni valós idejű lejátszásra
alkalmatlanok
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Mi köze ennek a fájlformátumhoz és a kodekhez?
• A lejátszás megkezdése előtt a teljes fájl letöltődik. A
lejátszáshoz szükséges valamennyi információ és erőforrás
helyben a fogadó számítógépben egyeztetetten rendelkezésre
áll. A tartalom lejátszható a kodekkel, menthető,
rendezhető, szerkeszthető, átkódolható,
sokszorosítható, árulható a tartalom
tulajdonosának bevonása nélkül.
•
Bármely értelmes felhasználó által beszerezhető és legálisan
birtokolható eszközzel a fentiekben felsorolt műveletek
elvégezhetők. Vita esetén nehezen választhatók szét a saját,
vagy oktatási célú felhasználások a kereskedelmi célú
alkalmazásoktól.
• Sűrű felhasználónál a hálózat túlterhelődik.
• Hirtelen csatornaváltás nem
lehetséges, még gigabites
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hozzáférésnél sem! médiakommunikáció. 2009.04. 29.
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Folyam protokollok beépítése a
webbe
• Előzőek alapján HTTP helyett
UDP alapú protokollok használata
• folyam protokollok
• gyorsan kezdi lejátszani és
nagymértékben tömörít
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Fájl formátumok
There are many video file formats to choose
from when creating video streams. The
most common formats are:
• Windows Media
• RealMedia
• Quicktime
• MPEG (in particular MPEG-4)
• Adobe Flash
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• There are pros and cons for each format but in
the end it comes down to personal preference.
Be aware that many of your users will have their
own preferences and some users will only use a
particular format, so if you want to reach the
widest possible audience you should create
separate files for each format. In reality this isn't
usually practical so you need to make a
judgment call on which formats to provide.
Obviously the better you understand all the
options, the better your decision is likely to be.
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Downloading
• When you download a file the entire file is saved on your
computer (usually in a temporary folder), which you then
open and view. This has some advantages (such as
quicker access to different parts of the file) but has the
big disadvantage of having to wait for the whole file to
download before any of it can be viewed. If the file is
quite small this may not be too much of an
inconvenience, but for large files and long presentations
it can be very off-putting.
• The easiest way to provide downloadable video files is to
use a simple hyperlink to the file. A slightly more
advanced method is to embed the file in a web page
using special HTML code.
• Delivering video files this way is known as HTTP
streaming or HTTP delivery. HTTP means Hyper Text
Transfer Protocol, and is the same protocol used to
deliver web pages. For this reason it is easy to set up
and use on almost any website, without requiring
additional software or special hosting plans.
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Streaming
• Streaming media works a bit differently — the
end user can start watching the file almost as
soon as it begins downloading. In effect, the file
is sent to the user in a (more or less) constant
stream, and the user watches it as it arrives. The
obvious advantage with this method is that no
waiting is involved. Streaming media has
additional advantages such as being able to
broadcast live events (sometimes referred to as
a webcast or netcast).
• True streaming video must be delivered from a
specialized streaming server.
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Progressive Downloading
• There is also a hybrid method known as
progressive download. In this method the
video clip is downloaded but begins
playing as soon as a portion of the file has
been received. This simulates true
streaming, but doesn't have all the
advantages
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Which Method to Use?
• The method you choose will depend on your
situation, but most people will opt for HTTP
streaming (download or progressive download).
This is the easiest and cheapest way to get
started. If necessary you can upgrade to a
streaming server later.
• Still, you will want to understand both options so
the next two pages of this tutorial look at each
one in a bit more detail. After that we'll talk about
how to create the actual video files.
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Streaming Video Servers
• A streaming media or streaming video server is a
specialized application which runs on an Internet server.
This is often referred to as "true streaming", since other
methods only simulate streaming. True streaming has
advantages such as:
• The ability to handle much larger traffic loads.
• The ability to detect users' connection speeds and
supply appropriate files automatically.
• The ability to broadcast live events.
• There are two ways to have access to a streaming
server:
• Operate you own server (by purchasing or leasing)
• Sign up for a hosted streaming plan with an ISP (Internet
Service Provider)
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Operate your own server
• To run your own streaming server, you can either
purchase a standalone server machine or purchase a
streaming server software package and install it on an
existing web server. Streaming software is available for
all common server platforms such as Linux, Windows,
etc.
• Some examples of streaming media software:
• Helix Universal Server from RealNetworks. This server
supports a variety of formats, including RealMedia,
Windows Media, Quicktime and MPEG-4.
• Apple Quicktime Streaming Server, supporting a few
formats including MPEG-4 and 3GPP.
• Macromedia Communication Server, specializing in
Flash-based video and interactive multimedia
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HTTP Streaming Video
• For this method you don't need any special type of website or
host — just a host server which recognises common video file
types (most standard hosting accounts do this). You also need
to know how to upload files and how to create hyperlinks
• There are some limitations to bear in mind regarding HTTP
streaming:
• HTTP streaming is a good option for websites with modest
traffic, i.e. less than about a dozen people viewing at the same
time. For heavier traffic a more serious streaming solution
should be considered.
• You can't stream live video, since the HTTP method only works
with complete files stored on the server.
• You can't automatically detect the end user's connection speed
using HTTP.
• HTTP streaming is not as efficient as other methods and will
incur a heavier server load.
• These things won't bother most website producers — it's
normally only when you get
into heavy traffic that you should
be
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To Create HTTP Streaming Video
•
•
•
•
•
Create a video file in a common streaming media
format
Upload the file to your web server
Make a simple hyperlink to the video file, or use
special HTML tags to embed the video in a web page.
That's essentially all there is to it. When a user clicks
the hyperlink, their media player opens and begins
streaming the video file. If the file is embedded, it plays
right there on the page.
Now let's look at how to create the necessary video
files...
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Create a Streaming Video File
• The methods below are for creating stored video files for
the purposes of streaming, not for providing live video
broadcasts. Live events must use a streaming server.
• There are two ways to create stored streaming video
files:
• Use a conversion utility program. This takes an existing
digital video file and converts it into the streaming format
of your choice.
• Export streaming files from video editing software such
as Adobe Premiere, Final Cut Pro, etc.
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Conversion Utilities
A conversion utility is a stand-alone program which imports
a video clip and exports it to a different format. Examples
include RealNetworks Real Producer and Sorenson
Squeeze Basically, you simply open a file and select
which which format to save it as. You can set various
parameters to optimise the final video. The program will
then chug away for some time while it makes the
conversion.
• In the window shown here, the pane on the left shows
the original file. The right pane shows the file as it is
being converted to a streaming media format.
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Streaming Video with Windows Media
Windows Media has the obvious advantage of being backed by the
biggest player in personal computing. It's a safe bet that Microsoft
won't be going broke or radically changing their business model any
time soon. Updates to the Windows Media Player are easy and
most people who run Windows have the correct player.
In our experience Windows Media performs well. Files are relatively
high quality and low size.
On the downside, Microsoft is renowned for frequently changing
formats and standards. As a video producer it can be difficult
keeping up with the latest version. Also, Microsoft is a very
proprietary format, and any platform other than Windows/IE may
have problems.
More info:
How to stream Windows Media from a web page
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Creating Windows
Media
files
with
Adobe
Premiere
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Streaming Video with RealMedia
• Real Media (www.real.com ) has an illustrious history and was one
of the first serious streaming video solutions. In the early days it was
widely considered to be the best streaming format. It is still a good
format but it has lost a lot of ground in the format wars.
• Real Media video images tend to be slightly less sharp than other
formats — this can be a good or bad thing depending on your
preferences. Moving images are handled reasonably well but the
finer detail can be easily lost. Overall image quality is perfectly
adequate for most applications.
• One big disadvantage is the difficulty in downloading the free Real
Media Player. Real Media has struggled to maintain a viable
commercial business model and they strongly encourage you to buy
the full version. This has led many people to become disillusioned
with the format and its reputation has not held up well over recent
years. Of all the common formats, Real Media looks like the one
which is struggling the most.
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Streaming Video Files with Quicktime
• Quicktime (www.apple.com/quicktime ) is a well-respected
format which has been around since the beginning of digital
video production. In many ways Quicktime is more complicated
than Windows Media or Real Media, but for most producers the
complexities don't actually matter. The average web designer
only really needs to know how to deal with Quicktime's .mov
(movie) files.
• If you are keen to explore Quicktime's advanced features, you'll
find that you can create interactive video, panoramas, virtual
reality settings and more.
• Some producers swear that Quicktime is the king of video
formats, others just can't seem to be able to make it work. Our
opinion is somewhere in between. It is certainly a good format
with many unique features. Getting good quality video can be a
challenge however — we find that default settings are rarely
good enough and experimentation is essential.
• One nice thing about Quicktime is its integration with other
products. It is widely supported by many editing, authoring and
general interest applications
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Streaming Video Files with MPEG-4
• MPEG-4 has had an interesting history since its
development in the late 1990s. Initially development was
supported my many companies including Apple and
Microsoft, but Microsoft has since abandoned active
support. Apple Quicktime continues to support MPEG-4,
as do other companies such as DIV-X .
• MPEG-4 is a very good quality standard with low file
sizes.
• The MPEG-4 standard is relatively complicated and can
be confusing. There are many variations of the format,
some are ISO-compliant and some aren't. Quicktime, for
example, deals with both ISO-compliant .mp4 files and
non-compliant .mov files. Some MPEG-4 files play in any
player, others will only work in certain players.
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Streaming Video using Flash
• Flash is a very serious force in the world of streaming video.
This is the format we recommend most strongly.
• Flash uses two main formats: .swf for standard Flash files
which are used in web pages, and .flv which is a special Flash
video format. flv files can be called from within swf files. As of
late 2008 Flash also supports H.264 files, which is a significant
leap forward.
• Flash has the disadvantage of being expensive. To get the most
from this format you need to own the Adobe Flash authoring
program. As well as being pricey, there's a lot to learn (although
if you have experience with video editors you will pick it up
quickly).
• On the plus side, if you can afford it and you're prepared for a
steep learning curve, Flash will give you power and flexibility
beyond your wildest dreams! Custom controls and menus,
interactive video and animations, advanced integration with
web pages... the sky is the limit.
• Flash also has the huge advantage of having the most widelyT.Gy. Intrernetes
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Adobe Flash Overview
Adobe Flash is a platform for creating digital media content,
including graphics, animation, audio, video and
interactive media. Flash is most commonly used to
display animated and/or interactive content on web
pages but it can be used for other applications as well. In
recent years Flash has also become a leader in online
video delivery.
• Flash content can be made either with the Flash
authoring program (known simply as Adobe Flash) or
third party applications such as Swish
(www.swishzone.com). Flash is by far the best solution
but it is fairly expensive.
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Flash content can be played back in two ways
• SWF files are the normal way to deliver Flash on the
Internet — the SWF file is embedded in a web page
using special HTML code. The end user must have the
Flash Player installed (most people do).
• Flash files can be created as standalone executable files
(.exe). These files run as a program in their own right
and do not require the Flash Player. This option is useful
for delivering content on CD or DVD.
• Flash Player
• Flash Player is a browser plugin that allows you to view
Flash files. Most browsers have the plugin installed by
default, but often the installed version is outdated.
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Flash Files
Flash uses the following file types and extensions
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Flash Player Version History
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Flash Player Version History II.
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Fájlformátum alapkérdések
•
•
•
•
Mi tudja lejátszani?
Mennyire tömör?
Kell-e jogdíjat fizetni?
Hogyan lehet áttenni más (a meglévő
eszközökkel lejátszható) formátumba?
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Audio Files
.aac
.aif
.iff
.m3u
.m4a
.mid
.midi
.mp3
.mpa
.ra
.ram
.wav
.wma
Advanced Audio Coding File
Audio Interchange File Format
Interchange File Format
Media Playlist File
MPEG-4 Audio File
MIDI File
MIDI File
MP3 Audio File
MPEG-2 Audio File
Real Audio File
Real Audio Media
WAVE Audio File
Windows Media Audio File
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•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
.3g2
.3gp
.asf
.asx
.avi
.flv
.mkv
.mov
.mp4
.mpg
.qt
.rm
.swf
.vob
.wmv
Video Files
3GPP2 Multimedia File
3GPP Multimedia File
Advanced Systems Format File
Microsoft ASF Redirector File
Audio Video Interleave File
Flash Video File
Matroska Video File
Apple QuickTime Movie
MPEG-4 Video File
MPEG Video File
Apple QuickTime Movie
Real Media File
Macromedia Flash Movie
DVD Video Object File
Windows Media Video File
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.mov files
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.qt files
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rm files
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vob files
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Free audio and video stream broadcasting
software
• Red5 (Free/Windows, Linux, Mac OS X)
Red5 is an open source flash server written in
Java that allows to broadcast MP3 and FLV files.
It supports:
• Broascasting streaming MP3 audio and FLV
video
• Recording client streams (FLV only)
• Shared objects
• Live stream publishing
• Remoting (AMF)
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Free audio and video stream broadcasting
software
• IceCast (Free/Windows, Linux)
You can broadcast streaming MP3 (MPEG
1 Layer 3 Audio) using an IceCast 1+,
streaming OGG Vorbis using IceCast 2+,
streaming AAC using IceCast 2.2+
streaming server.
Icecast was designed to be Shoutcast
compatible. Unlike the commercial
Shoutcast product Icecast is free.
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Free audio and video stream broadcasting
software
• VideoLan (Free/Windows, Linux, Mac OS X, BeOS ...)
The VideoLAN streaming solution includes:
• VLS (VideoLAN Server), which can stream MPEG-1, MPEG-2 and
MPEG-4 files, DVDs, digital satellite channels, digital terrestial
television channels and live videos on the network in unicast or
multicast,
• VLC (initially VideoLAN Client), which can be used as a server to
stream MPEG-1, MPEG-2 and MPEG-4 / DivX files, DVDs and live
videos on the network in unicast or multicast; or used as a client to
receive, decode and display MPEG streams under multiple
operating systems.
• VLC's stream output works under Linux, Windows, Mac OS X,
BeOS and many Unices. VLS works under Linux, Windows and Mac
OS X.
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Free audio and video stream broadcasting
software
• NullSoft Video at SVCI (Free)
NSV is a new multimedia container format designed for
network video streaming. The format is known as
NullSoft Video or simply NSV. NSV was developed by
Nullsoft corporation, the same company that produced
the popular Winamp and Shoutcast streaming audio
software. Winamp TV uses NSV streams.
NSV consists of free software to encode, stream and
view video. There are additional third party NSV
applications being developed and distributed by stations
and users. Additional software can be purchased from
outside commercial software vendors as well.
NSV has broken the restrictive Internet video broadcast
barrier and allows anyone the ability to produce and
distribute live or recorded video content.
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Free audio and video stream broadcasting
software
• MPEG4IP (Free / Linux, Windows, Solaris, FreeBSD, BSD/OS, Mac
OS X)
MPEG4IP provides an end-to-end system to explore streaming
multimedia. The package includes many existing open source
packages and the "glue" to integrate them together. This is a tool for
streaming video and audio that is standards-oriented and free from
proprietary protocols and extensions.
Provided are a live MPEG-4/H.261/MPEG-2/H.263 MP3/AAC/AMR
broadcaster and file recorder, command line utilities such as an MP4
file creator and hinter, and an player that can both stream and
playback from local file.
This code is not intended for end users, and does not contain
executables. Please read all the legal information to determine if it is
suitable for you.
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