streaming media production best practices streaming media east – may 16 th, 2005 steve mack, lux...
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Streaming Media Production
Best PracticesStreaming Media East – May 16th, 2005
Steve Mack, LUX [email protected]
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What Is Not Covered
• Any particular streaming media platform– QuickTime, RealSystem and Windows Media all shown
• Alternative data types– Flash animation, text, images, etc.
• Advanced authoring– JavaScript, VB, SMIL, MPEG 4
• Serving• Business Models
– Advertising, Pay-Per-View, etc.
• Digital Rights Management– Securing your content
3
Today’s Agenda
• Part I – The Basics (~1 hour)– Terminology, basic concepts
• Part II – Creation (~2 hours)– Audio– Video
• Part III – Encoding (1 hour)– Encoding Basics– Advanced Encoding– Platform specific examples
• Part IV - Authoring (1 hour)– Authoring Basics (metafiles)– Advanced Authoring (embedded players)
• Part V – Live Broadcasts (time allowing)
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Agenda – Part I
• Basic Concepts• Streaming Media System Components &
Terminology• The Streaming Media Process• Tools of the trade• Streaming Media Technologies
– QuickTime– RealSystem– Windows Media– Flash MX– MPEG 4
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Internet Access Devices, Worldwide
0
200
400
600
800
1000
2002 2003 2004 2005
1 Billion
Sources: Cahners In-Stat Group
PC’s Internet Connected Mobile Phones, PDAs, Set-top Boxes
(mill
ion
s)
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What Does It All Mean?
• Streaming media is a new mass medium– Currently in its second wave
• New platform(s) for media delivery• Huge audience• Huge opportunity
– Entertainment, business, education, you name it– Won’t last forever
We believe you.
Get to the point.
Okay, I will. Let’s start at the beginning…
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Streaming is not Downloading
• Streaming– Real time– Live or on demand– Not stored locally
• Downloading– Entire file must download– Not real time, not live, and stored locally
• Progressive Download– Hybrid approach– Player estimates how much to buffer– Can be very effective for short-form content
• Advantages and disadvantages of downloading
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How Streaming Media Works
Encoding software converts raw media into a format that can be streamed
Audience uses player software (RealOne, QuickTime, Windows Media) to watch/listen.
Serving software distributes the streams to listeners
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Streaming Media System Components
• Players– QuickTime, RealPlayer, Windows Media Player, etc.
• Servers– Servers are specialized computers built specifically to
serve user requests
• Encoders– Encoders can be hardware or software, available from a
number of manufacturers
• All streaming media systems are built from these three basic building blocks
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Streaming Media Delivery Methods
• Unicast– Each user receives an individual stream– Doesn’t scale well
• Multicast– A single copy of the stream is sent out– Each viewer grabs a copy– Requires all routers to be “multicast-enabled”– Only suitable for live broadcasts– Doesn’t work on today’s internet
• Many Internet broadcasts (webcasts) are done using a combination of the two
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Streaming Media Delivery Methods
• Unicast or multicast to secondary servers• Unicast or multicast to local clients
13
Streaming Media Terminology
• Protocols– Determine how components communicate
(RTSP, RTP, MMS, HTTP, TCP/IP, UDP)
• File Formats– How the data is structured– Generally proprietary (except for MPEG4)
(.asf, .rm, .qt, etc.)
• Codecs– Contraction of coder-decoder (or compressor –decompressor)
– Software that reduces the data rate of media files – Codecs are necessary because …
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Bandwidth Is Everything
• Bandwidth is the measurement of how much data can be received in real time
• Streaming media delivery is limited by audience bandwidth
• Available bandwidth determines quality • How best to utilize available bandwidth?
– Screen sizes for videos– Quality of audio– How much free bandwidth to leave
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The Streaming Media Process
• Production– A/V Production, digitizing the raw media files, editing
• Encoding– Converting to a streaming format
• Authoring– Connecting the audience to your content– Creating an interface for your content – Combining multiple data types
• Serving– Distributing your content to the public
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Streaming Media Tools
• Production Tools– Audio/Video equipment, editing hardware/software
• Encoding Tools– Encoding hardware/software
• Authoring Tools– Authoring software (WYSIWYG, text editors)
• Serving Tools– Server hardware
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Tools of the Trade
• Audio – Good source: good microphone, mixing desk– Signal processing: compressor, EQ unit – proper recording environment
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Tools of the Trade (cont’d)
• Video– Good camera: DV is most cost-efficient, FireWire option– Buy the best tripod you can afford!– Lighting: 3-point lighting kit
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Tools of the Trade (cont’d)
• Computer Hardware– No such thing as too much CPU/RAM/storage– Professional sound cards sound better– USB audio interfaces a new option– FireWire cards best bet for video capture
• Software– Audio and video editing software, encoding software
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Streaming Media Systems - The “Big Three”
• QuickTime– Current version –7.0 (Mac OSX), 6.5 (Win)
– Sorenson and MPEG-4 (H.264) codecs
– Free server & player; QuickTime Pro $29.95
• Windows Media– Current version – Player 10 (Win XP only), 9 series player and
encoder (no live encoding on Mac)
– Windows Media codecs
– Free player, encoder & utilities; Windows Server 2003
• RealSystem– Current version – RealPlayer & RealProducer 10, Helix Server
– RealAudio & RealVideo codecs, also plays back & streams QuickTime & Windows Media
– Licensed server, free player & encoder
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Streaming Media Systems - New Kids on the Block
• Flash MX– Currently on version 1.5– Sorenson codec (recently licensed VP6)– Streaming requires Flash Player 7, Sorenson Squeeze
or QuickTime Pro encoding, Flash MX required for streaming and authoring
• MPEG 4– ISO standard (Moving Picture Experts Group)– A standardized framework for interactive media,
including streaming, including a file format & codec– QuickTime & RealPlayer support
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Streaming Media in Action
• QuickTime– QuickTime Pro
• RealSystem– Real Player 10, RealProducer 10
• Windows Media– Windows Media 9 Series
• Flash MX– Version 1.5
• MPEG 4– Sorenson Squeeze
Quick Break
Coming Up: Part II - Production
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Agenda – Part II
• Streaming Media Process Recap• Codecs
– What they are and why they’re necessary
• Creation – Audio– Audio Codecs– Production Tips– Processing Techniques
• Creation – Video– Video codecs– Production Tips– Processing Techniques
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The Streaming Media Process
• Production– A/V Production, digitizing the raw media files, editing
• Encoding– Converting to a streaming format
• Authoring– Connecting the audience to your content– Creating an interface for your content – Combining multiple data types
• Serving– Distributing your content to the public
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Remember: Bandwidth is Everything
• Typical bandwidths:– dial-up: 37kbps– Broadband: ~2-300kbps
• Uncompressed audio = ~1400Kbps– 44.1Khz*16bits*2 channels
• Uncompressed NTSC video = ~30MBps– 720*480pixels*24bits*30frames/second– that’s roughly 237,000bps, folks!
• We must reduce the data rate while maintaining fidelity
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How Codecs Work
• Codecs use complex perceptual models to figure out what we perceive vs. what we hear– Audio
• Hear: 20 – 20,000Hz; over 120dB dynamic range• Perceive: Most sensitive in the midrange; loud
sounds “mask” quiet sounds
– Video • See: full spectrum, 180 degree field of vision• Perceive: Most sensitive to motion and color
• Codecs use this info to determine what is most important; discard the rest– Important to produce content with this in mind
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Audio Production Tips
• Remember: G-I-G-O• Use good equipment and solid audio
engineering practice – Good equipment, microphone technique– Set up a proper gain structure
• Use signal processing to optimize – Compression and EQ can be used to optimize as
needed
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Audio Production Tips
• Use good quality microphones– Directional hand-held mics for reporting environments– Lavaliere mics for stationary talent– Shotgun microphone on a boom for location work
• Don’t forget your windsock(s) for outdoor work
– Avoid using the on-camera mic
• Use balanced cables (XLR or ¼” TRS)– Better signal level, more noise resistant– Use Professional XLR adapter if necessary
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Production Tips - Location Audio
• Large, quiet, isolated locations are best– Need room to move– Keep noisy machinery away from
microphones– Small rooms sound “small”
• Treat reflective surfaces– Hard flat surfaces reflect sound– Acoustic foam, curtains, & tablecloths
• Outdoors– Challenges can be overcome
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Setting Up A Gain Structure
• Make sure each piece of equipment operates in its optimal range
• Start with first piece of equipment and work through the signal chain
• set the input and output gain for each• Peaks at -3dB for analog, -10dB for digital
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Signal Processing - Compression
• Remember: Codecs assume loud signals are most important
• Compression “evens out” audio levels – Protects your equipment from “spikes” in audio level– Attenuating loud sections enables overall signal gain– “Fattens” audio– Hardware compressor is essential for live broadcasts
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How Compression works
• Set a threshold, a ratio, and a post-compression gain– Start with a threshold of –10db, 4:1 ratio, and set gain to
match original signal level– Voice is much more compression tolerant than music
Compressionin action
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Signal Processing – Equalization
• EQ is turning up or down certain frequencies
• Ears are most sensitive to midrange• Use EQ to improve the tonal quality of
your audio– Add “sparkle,” “air,” “warmth,” & “presence”– Remove “rumble,” “hiss,” “clutter,” “harshness”
• How?– Find the right frequency, and turn the knob!– Just like adjusting your car stereo or clock radio
EQ example
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Useful EQ Frequencies
EQ Range Contents20–60 Hz Extreme low bass. Most speakers cannot reproduce this.
60–250 Hz The audible low-end. Files with the right amount of low end sound warm, files without enough sound thin.
250 Hz–2 kHz The low-midrange. Files with too much in the low-mids are hard to listen to and sound telephone-like.
2 kHz–4 kHz The high-midrange. Where most speech information resides. In fact, cutting here in the music and boosting around 3 kHz in your narration makes it more intelligible.
4 kHz–6 kHz The presence range. Provides clarity in both voice and musical instruments. Boosting 5 kHz can make your music or voiceover (not both!) seem closer to the listener.
6 kHz–20 kHz The very high frequencies. Boosting here adds “air” but can also cause sibilance problems
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How Video Codecs Work
• Intra-frame compression– Just like a .jpg or .png file
• Inter-frame compression– Differences between frames are encoded
• Key frames– Entire frame is encoded– Uses a lot of bandwidth
• Difference frames– Only differences are encoded– Use relatively little bandwidth on low motion content
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Video Production Tips
• Avoid unnecessary motion/changes– Use a tripod, use a tripod, use a tripod– Avoid moving objects in the background– Avoid special effects– Simple edits are best– Keep the number of cuts to a minimum
• Framing– Smaller screen, so frame tighter
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Video Production Tips
• G-I-G-O• Use good video engineering practice
– If you don’t know, hire someone
• Good equipment, proper technique– If you don’t own it, rent it
• Lighting is essential– Nearly impossible to correct using software– Low-light = no light
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Video Production Tips
• The 3-point Lighting system– The basis of virtually all lighting– Key light
• The main light for the scene• Generally 15 - 60° from camera
– Fill light• “Fills in” the hard shadows of the key light• On opposite side of camera from key light
– Back light• Separates the subject from the background• Above & behind the subject
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Video Production Tips
• White balance– Best to set manually
• Camera filters– UV filters can make outdoor shoots less hazy– Fluorescent filters can make indoor office shoots look
less anemic– Diffusion filters can soften the image and make it look
less harsh, more “film-like”• Amount of diffusion to use depends on your camera• http://videosystems.com/ar/
video_curse_digital_video/index.htm
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Digitizing Video
• Capture cards– Low end fine for most streaming applications– High end definitely provide better quality
• FireWire (IEEE 1394, iLink)– Enables direct digital video transfer– Available on most pro-sumer DV camcorders
• External FireWire devices– Take analog inputs (S-Video, composite) and convert to
DV via FireWire– 5:1 compression, but very cost effective
42
Video Processing Techniques
• VGA vs. Television displays– VGA screens are far more detailed – Traditional video tends to look dark & washed out
• Adjust Brightness– Add gain to match screen to a TV monitor– Be careful if you’re going back out to the broadcast world!
• Adjust Contrast– Adding a small amount is good; be careful though– Too much contrast adds grain (bad for codecs)
• Color– Increasing saturation a bit can be helpful
43
Working With Video
• Be sure to use the correct pixel aspect ratio– TV pixels are slightly taller than wide; VGA pixels are
square– TV resolution is approximately 720 x 480, but when
displayed appears to be 4:3– You must resize to a 4:3 aspect ratio if a VGA screen is
your final destination• 640x480, 320x240, 240x180, etc.
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Encoding
• Remember: Bandwidth is Everything• Make choices depending on audience
bandwidth– Total bit rate– Audio bits vs. video bits– Optimizing your encoding settings
• Audio• video
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Audio – Encoding Choices
• Total bit rate for audio– 8kbps - minimum– 16kbps – good quality– 32kbps - FM quality– 64kbps – “CD quality”
• Stereo vs. Mono– Most program content is mono– Mono codecs have better fidelity – Music can benefit from stereo encoding– Use mono below 32kbps
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Audio – Encoding Choices
• Music vs. speech codecs– Speech has limited dynamic & frequency range– Speech sounds decent through a music codec– Music sounds horrible through a speech codec– When in doubt, stick to a music codec– Windows Media 9 Series has a new hybrid codec (cool!)
but…• Not entirely backwards compatible• New codec install available for legacy players, but
not automatic – must be installed
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Video - Encoding Choices
• Allot the correct amount for audio– Audio tells the story– People will tolerate poor video with good audio
• the inverse is not true
• Choose the right screen size (resolution)– Codecs encode to whatever specifications you provide– High action video content requires lower resolution; low
action content can be larger– Rule of Thumb: It’s better to reduce the resolution rather
than the frame rate• Less frames = more differences between frames• More differences = more to encode
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Video - Encoding Choices
• Choosing a Frame Rate / Frame Quality– Less high quality frames, or more low quality frames?
• Limiting the frame rate – Choose factors of the native frame rate– 29.97, 15, 10, 7.5, 6, 5 for NTSC video (30fps)– 25, 12.5, 8.67, 6.25, 5 for PAL video (25fps)– 24, 12, 8, 6 for film (24fps)
• QuickTime/Windows Media– set frame rate & quality
• RealMedia– Choose video quality (sharp/normal/smooth)
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Cropping & Resizing
• Important to maintain the correct aspect ratio
• Resizing– Always resize to a 4:3 aspect ratio for VGA displays
• Cropping– Overscan – garbage around edge of screen usually
hidden by TVs – crop!– Safe to crop up to 10% (title safe area)– Be sure to crop consistently, maintain 4:3 aspect ratio
• Widescreen content – Can crop to a letterbox format– If captured 4:3, resize 4:3, then crop to 16:9 – If captured 16:9, resize & crop 16:9
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Suggested Encoding Settings
Audience Connection
Streaming Bit Rate
Video resolution
Audio Bit Rate
56k modem 34kbps 160x120, 176x132
8-10kbps
xDSL, Cable 300kbps 320x240 32-64kbps
High bit rate (LAN multicast)
700kbps 640x480 64-96kbps
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Advanced Encoding Techniques
• 2-Pass encoding– Allows codec to “map out” the encode– Beneficial but doubles encoding time
• Variable Bit Rate (VBR)– VBR improves quality but can be unsuitable for
streaming• High data peaks can lead to re-buffering• Sorenson V3 has a new 1-pass VBR that improves
quality and streams well (limits peaks)
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Advanced Encoding Filters
• De-Interlacing– Artifacts arising from the difference between interlaced
(TV) and non-interlaced (VGA) displays
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Interlacing Artifacts
• Can be interpolated, blended, or discarded
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Advanced Encoding Filters
• Inverse Telecine– Artifacts arising from the process where film content
(24fps) is transferred to video (30fps)– Extra frames should are removed
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Advanced Encoding Filters
• Noise Reduction (actually a blur filter)– Codecs interpret grain (noise) as motion; by blurring the
frame slightly you can reduce the graininess
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Encoding Examples
• QuickTime– Use QuickTime Pro– Simply open up a raw media file, and save it as a
streaming file
• RealSystem– Use RealProducer– Session based
• Windows Media– Use Windows Media Encoder– Session & profile based
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Authoring
• Problem: browsers don’t stream– Browsers don’t understand RTSP or MMS protocols
– Browsers download entire file
• Solution: metafiles– Small file delivered via HTTP
– Contains information about streaming file
4
Web Server
Streaming Server
1
2
3
5
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Authoring - Metafiles
• QuickTime .qtl files
• RealSystem .ram files
• Windows Media .asx files
<?xml version="1.0"><?quicktime type="application/x-quicktime-media-link"?><embed src=“rtsp://your.qtserver.com/YourStream.mov" />
rtsp://your.realserver.com/YourStream.rm
<asx version="3.0"> <entry> <ref ref="mms://your.wmserver.com/YourStream.wmv" /> </entry></asx>
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Metafile Parameters
• QuickTime– Included in <embed> parameter
– loop, autoplay, fullscreen, controller, quitwhendone (= true/false)
– qtnext (for playlists)
• RealSystem .ram files– Place after “?” following URL; separate with “&”
– title, author, copyright, start, end
– Many others for dictating look of player
• Windows Media .asx files– Place in name-value pairs in <param> tag
– title, author, copyright, starttime, duration, repeat
– Many others
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Metafile Parameters
• QuickTime .qtl files
• RealSystem .ram files
• Windows Media .asx files
<?xml version="1.0"><?quicktime type="application/x-quicktime-media-link"?><embed src=“rtsp://your.qtserver.com/YourStream.mov" autoplay=“true” fullscreen=“true” />
rtsp://your.realserver.com/YourStream.rm?start=:30&end=“2:21”
<asx version="3.0"> <entry> <ref ref="mms://your.wmserver.com/YourStream.wmv" /> <param name=“starttime” value=“30” /> <param name=“title” value=“My Stream” /> </entry></asx>
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Embedded Players
• Special HTML code to embed the player• Different code required depending on
browser– IE uses ActiveX control (except on Mac)– Netscape-based browsers use a Plug-in
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Embedded Players
• IE-based browsers use the <object> tag
• Netscape-based browsers use <embed>
<object classid="clsid:02BF25D5-8C17-4B23-BC80-D3488ABDDC6B"
codebase="http://www.apple.com/qtactivex/qtplugin.cab“
width="160" height="136" >
<param name="src" value="YourRefMovie.mov">
</object>
<embed src="YourRefMovie.mov" width="160" height="136"
pluginspage="http://www.apple.com/quicktime/download/">
</embed>
You can use both for cross-browser compatibility – sort of.
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Embedded Players – QuickTime
• Use both for cross browser compatibility– IE ignores the <embed> tags– Netscape-based browsers ignore the <object> tags
• NS 6.x is broken
<object classid="clsid:02BF25D5-8C17-4B23-BC80-D3488ABDDC6B"
codebase="http://www.apple.com/qtactivex/qtplugin.cab“
width="160" height="136" >
<param name="src" value="YourRefMovie.mov">
<embed src="YourRefMovie.mov" width="160" height="136"
pluginspage="http://www.apple.com/quicktime/download/">
</embed>
</object>
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Embedded Players - RealPlayer
• Each part of the RealPlayer is embedded separately, I.e.:– “ImageWindow” – the video display– “All” – all the controls, or can be embedded individually
• Each part requires code• All tied together with the console
parameter
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Embedded Players – RealPlayer
<!– code for Image Window --><object classid="clsid:CFCDAA03-8BE4-11cf-B84B-0020AFBBCCFA" width="240" height="180"> <param NAME="controls" VALUE="ImageWindow" /> <param NAME="console" VALUE="one" /> <param NAME="src" VALUE="media/MyMovie_240x180.rpm"/> <embed src="media/MyMovie_240x180.rpm" width="240" height="180" controls="ImageWindow" console="one" /></object>
<!-- code for controls --><object classid="clsid:CFCDAA03-8BE4-11cf-B84B-0020AFBBCCFA" width="375" height="100"> <param NAME="controls" VALUE="All"/> <param NAME="console" VALUE="one"/> <embed src="media/MyMovie_240x180.rpm" width="375" height="100" controls="All" console="one" /></object>
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Embedded Players – Windows Media
• It gets tricky for a number of reasons– Windows Media discontinued support for the Netscape
plug-in with the 7.0 player– The 6.4 plug-in doesn't work on some Netscape
browsers (NS6, NS7.0)– IE on Mac uses the Netscape plug-in
– WM9S resumed support for the plug-in!!• Requires WM9S
– Netscape 7.1 now supports the ActiveX control!
69
Embedded Players – Windows Media
• If you want to support the widest possible audience:
Player/Browser NS 4.x
NS 6.x, 7.0
NS 7.1 IE Win IE MacSafari Mac
WMP 6.4 Yes No Yes* Yes Yes No
WMP 7.0, 8.0
No (use 6.4)
No Yes* YesNo (Use
6.4)No
WMP 9.0 Yes Yes Yes* Yes
Yes (Java Applet**, natively on OSX)
Yes (OSX)
* Netscape 7.1 now supports the Windows Media ActiveX control
** Java Applet solution is dependent on user environment
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Embedded Players – Windows Media
• Use nested <object> & <embed> tags• Different players have different sized
controls– 6.4 – 46px; 7.0 – 40px; 9.0 – 45px.– Tricky to predict which player is installed – Player will squeeze video window into available space
<object id="WMTPlayer" width="240" height="244" classid="CLSID:6BF52A52-394A-11d3-B153-00C04F79FAA6"> <param name="url" value="media/wmv9.asx"/> <embed type="application/x-mplayer2" src="media/wmv9.asx" width="240" height="226"> </embed> </object>
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Embedded Players - tips
• Keep it simple• Don’t forget to leave room for the control
bar in your display window– QuickTime – 16 pixels– RealPlayer – 36 pixels for controls, 30-55 more for
additional info (suggested – will scale)– Windows Media – depends on player
• Don’t forget the codebase and/or pluginspage parameters so users can get the player if they don’t have it installed
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Embedded Players - tips
• You can get even fancier with JavaScript or VBScript, but beware…– Cross browser incompatibilities
• Netscape Plug-in vs. ActiveX controls
– Cross platform incompatibilities• No NS plug-in for WM9S• IE on Mac uses NS plug-in
74
Live Concerns
• You only get one shot – no room for error• Redundancy is key – you need two of
everything• Any processing must happen in real time,
so you should consider hardware, such as an audio compressor
• You may want to be conservative with your encoding settings to increase your chance of success
75
Live Broadcast Decision Tree
• Connectivity on site?– Can connectivity be installed in time?
• Has Permission been granted?– Call all partied involved (talent, venue, label, etc)
• Sufficient Budget?• Suitable Location
– Audio?– Video?– Power?
• All of the above must be satisfied
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Live Concerns - Connectivity
• Send raw media back to Broadcast Operations Center (BOC)– Satellite– Vivyx (fiber)– Wireless
• Send encoded streams back to BOC– Need IP connectivity on site– Minimum 8 week install window
77
Live Concerns - Creation
• Redundancy demands lots of additional equipment– At least one backup of all critical hardware
• Additional crew required• Remote locations put a strain on
equipment and are not easily controlled• May need additional a/v for pre- & post-
show• Need communication between crew
members, on site & BOC– Don't rely on cell phones– Land lines are best– AIM a great tool
78
Live Concerns - Encoding
• Longer events imply longer listening times– May want to be conservative with bit rate
• Faster machines required to encode highest quality in real-time
• Backup machines required
79
Live Concerns - Authoring
• Simplify web sites to speed up access to stream– Nobody likes having to register– Don't make them traverse entire site– Complicated pages with lots of graphics/animation might
cause the web server to fail
• If you must use an embedded player, at least offer a link to a metafile
80
Live Concerns – Serving
• Vastly increased bandwidth demands• Increased server licensing demands
(RealSystem only)• Need more servers
– Load balancing system is crucial
81
Live Encoding – Examples
• RealSystem• Windows Media
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Where to Find More Information
• Buy the book!– Streaming Media Bible, published by Wiley– Over 1000 pages of streaming media tips & tricks
• Companion Web Site– http://www.streamingmediabible.com
• Trained Audio Engineers & Videographers:– The best possible resource– Can be friendly if treated well– Generally need the work
• Ask me– [email protected]
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Glossary
Artifact Distortions such as jagged edges or metallic sounds that are introduced into file during encoding.
Codec An algorithm used to reduce file sizes.
Constant Bit Rate (CBR)
An approach to encoding data that keeps the bit rate constant throughout. This approach is more suited to streaming media.
De-interlacing Removing the artifacts from an interlaced (TV) signal.
Equalization (EQ) Changing the sound of an audio file by boosting or attenuating certain frequencies.
Field One-half of an interlaced video frame, consisting of either the odd or the even numbered scan lines.
85
Glossary (cont’d)
Firewall A security system designed to allow only certain kinds of traffic in and out of
networks.
HTTP Hypertext Transfer Protocol, used by web servers to deliver web pages. Can be used by streaming servers to deliver streams across firewalls.
FireWire (IEEE 1394, iLink)
A standard for exchanging digital information, such as audio or video. Since the information is exchanged digitally, it is lossless.
Gain, gain structure The amount of amplification being applied. The gain structure of an audio setup refers to the amount of amplification being applied at each stage.
Inverse Telecine Removing the extra fields inserted into a video signal when film is transferred to video.
86
Glossary (cont’d)
Key Frame In encoded video, a frame that contains information about the whole frame, as opposed to a difference frame which only contains information about what is different between it and the previous frame.
Metadata, metafile Metadata is data about other data. A metafile, therefore, is data about another file, such as the location of a streaming media file.
MIME type Used by applications such as browsers to determine what program is used to view the file.
MMS Microsoft Media Server, protocol used by Microsoft server to send streams across the internet (will change to RTSP)
Multicasting A method of broadcasting on the internet where multiple users can “tune in” to the same stream. Only applicable in closed networks, not the public Internet.
87
Glossary (cont’d)
Normalization Maximizing the volume of an audio file without distortion.
NTSC The broadcast standard for television signals in the United States, which specifies 30 frames (60 fields) per second, 525 lines of resolution (~480 visible).
Overscan The area of a broadcast video image that is normally hidden by the plastic surrounds of a television monitor.
PAL The broadcast standard for television signals in most European countries, which specifies 25 interlaced frames (50 fields) per second, 625 lines of resolution (~576 visible).
Port (number) Networking applications use ports to determine which application receives the data being sent.
88
Glossary (cont’d)
RTSP Real Time Streaming Protocol, used by QuickTime and RealSystem (soon Windows Media) to send streams across the Internet
SMIL An open, standardized language for combining multiple data types into a single multimedia presentation.
Variable Bit Rate (VBR) A system of encoding that allots variable amounts of bits to different sections of the file. VBR in general is not suitable for streaming due to the large variation in data rate.