Data Rates for Streaming Video
The Encoding Method pop-up menu contains three items. Choosing the first two encoding methods produces a H263 format video stream, which is best suited for general purpose video. The third encoding method consists of a separate video codec that uses a Macromedia proprietary codec optimized for screen recordings. You can choose from these three encoding methods:
Baseline (1 Pass) uses a consistent bit rate to encode the video stream. The resulting file size is closely related to the value entered in the Limit Data Rate To text field, because the data rate will not vary on a frame-by-frame basis regardless of the complexity and changes in the video stream.
Better (1 Pass VBR) allows the data rate to fluctuate based on the content in the video sequence, allocating more bits to areas of greater complexity. This setting produces better image quality, takes longer to process, and does not produce easily predictable file sizes (because the bit rate fluctuates depending on footage). Screen Recording Codec enables you to record screen operations to a lossless compression. When you select this option, all other video options become inactive (are grayed out). Only choose this encoding method when encoding footage that was created either in screen recording applications or by compositing graphic elements together in an editing or effects application. The codec records all pixel changes in the video stream, which is ideal if there is very little variation in the video (such as screen recordings of software application demonstrations), but will produce very large files when used with true video source footage.
Frames Per Second
The Frames Per Second text field enables you to specify the frame rate for the encoded FLV file. To maintain the temporal quality of the original source clip, use the same frame rate. For full motion NTSC use 29.97 fps; for PAL use 25 fps. If you lower the frame rate (which can significantly reduce the video data that needs to be encoded), the Flash Video Exporter plug-in will drop frames at a linear rate to achieve the new fps rate. Be sure to choose an evenly divisible fraction of the original frame rate, or you may introduce highly distracting “stepping” artifacts.
Note that 30 and 24 fps are not actually accurate frame rates in common use. (See the section "Technical Discussion of Video Fundamentals" for additional information on the NTSC and PAL video standards.)
To keep audio and video in synch when creating long FLV files (longer than a couple of minutes), you must use the accurate frame rates when downsampling the fps rate.
The pop-up menu to the right of the Frames Per Second text field enables you to cycle through the commonly used frame rates, but you can enter any frame rate you want in the Frames Per Second text field.
Use the Quality pop-up menu to specify the estimated data rate settings for encoding video at a low, medium, or high quality. This option controls the value in the Limit Data Rate To text field by computing an approximate data rate based on the file's frame rate (fps) and size (horizontal and vertical pixels). If you change the value in the Frames Per Second, Height, and Width text fields, Flash Video Exporter updates the value in the Limit Data Rate To text field to reflect the new quality settings. For example, if you change the frame rate from 24fps to 12fps, then the value in the Limit Data Rate To text field will be reduced by exactly 50 percent, because the required bit rate to maintain the given quality level is exactly half if you reduce the number of frames per second by half.
If the available Quality setting options do not produce the desired quality results with your particular source footage, select Custom, and then enter a higher data rate into the Limit Data Rate To text field.
Limit Data Rate
This setting is the key “quality” variable and indicates the number of bits per second that are allocated to encode the video. Larger bit rates produce larger files with higher image quality.
The Flash Video Exporter dialog box displays data rate limit in kilobits or kilobytes per second. You can choose the unit you want from the pop-up menu to the right of the Limit Data Rate To text field. Some users might prefer to think in terms of kilobits while others think in terms of kilobytes. Those with a background in web development are familiar with bits and kilobits, because it is a web developer’s duty to keep files as small as possible for quick downloads. Those with a background in print or video are accustomed to working with file sizes in the kilobyte, megabyte, and even gigabyte range and therefore might prefer to work with kilobytes. Simply put, there are 8 bits in a byte, 8 Kbits in 1 KB, 8 Mbits in 1 MB, and so on.).
When you enter a value x in the Limit Data Rate To text field, you are essentially telling Flesh Video Exporter, “do not make my final file size larger than x kilobits or kilobytes for every second. If you have a 10 second clip and enter a value of 100 KB/sec, you’d end up with a clip no larger than 1,000 KB, or 1 MB. In order to keep down the file size encoders will sacrifice image quality. To keep the image quality consistent, you can scale down the clip so fewer pixels per second are represented, or lower the frame rate so less frames per second are displayed. When exporting files, you must find the right balance between image size, file size, and frame rate. For best results, consider your target delivery medium.
For Internet delivery most FLV files are downloaded progressively to the client computer and then played back from the local hard disk. This technique provides a wide gamut of bit rates for delivery. For streaming FLV files, client connection speeds limit the bit rate that you can use. Table 4 shows the approximate total download times for a one- and five-minute video clip encoded at 500 kilobits and 2,000 kilobits.
Both clips assume no audio (MOS).
Table 5 lists the approximate data rates that you can use with Flash Communication Server to reliably stream video to target users on various connection speeds. These data rates include a 10-percent headroom to allow for network traffic.
The Keyframes pop-up menu enables you to choose between automatic or custom keyframing. The Keyframe value indicates to the encoder how often to re-evaluate the video image and record a full frame, or keyframe, into the FLV file.
Between keyframes the encoder approximates the full frame by estimating the full value of all pixels on the screen, principally by comparing multiple frames and eliminating information that is redundant. The Keyframe value can be any number up to 100. When you select Auto, Flash Video Exporter chooses a keyframe rate that is a multiple of the current frame rate.
The Auto setting is a good starting point for all video footage. If your footage has a lot of scene changes or rapidly moving motion or animation, then the overall image quality may benefit from a lower keyframe value. In general, a higher keyframe rate produces better image quality because bits are not wasted describing the areas of an image that remain unchanged from frame to frame.
There is a very important dependency on the keyframe rate, which refers to the ability of Flash Player to seek (fast forward, rewind) through an FLV file. Flash Player can only frame advance to keyframes, so if you want to be able to skip around to different places and pause the frames, you must use a lower keyframe value. If you want to be able to advance to every frame in the FLV file, use a keyframe value of 1. When you reduce the keyframe value, you must raise the data rate for the Flash video in order to maintain comparable image quality.
The Flash Video Exporter encoder analyzes the differences and similarities between adjacent frames, and allocates bits depending on this information. Using the Motion Estimation pop-up menu, you can choose between Faster, which results in faster estimation of motion at the sacrifice of quality, or Better, which results in a more accurate estimation of motion at the sacrifice of speed.
The Bitrate pop-up menu under Audio enables you to set the bit rate of your MP3 audio stream. Full audio tracks, such as music and significant background noise, require a higher bit rate. Simple dialogue, such as with a “talking head” shot, can be compressed to a much higher degree. Higher bit rate settings are encoded in stereo, while lower bit rate settings are encoded mono.
The Resize To pop-up menu enables you to scale your footage on output. The pop-up menu lists a number of common preset sizes, but you can enter a size of your choice in the Width and Height text boxes.
You can also designate the output size by entering a percentage value of the source size rather than an arbitrary pixel value.To keep the aspect ratio (the ratio of width to height) of the source video file, select the Lock Aspect Ratio check box. Leave this box unchecked, if you want to export your video at a different aspect ratio than the source file.
In some third-party applications the source file’s image size may not automatically show up in the Flash Video Exporter dialog box. In these cases, if you want to constrain the proportions you enter the source file’s pixel dimensions, select the Lock Aspect Ratio check box, and then resize the image. If your source video is made up of non-square pixels, such as D1 or DV video, use the scale function to scale the image non-proportionately down to a 4:3 aspect ratio. For example, if your source file is 720 x 480 (DV NTSC), then scaling to 320 x 240 (correct aspect ratio) will require a non-proportional scale (greater change in X axis than Y).
De-interlacingWhen encoding interlaced source footage (any NTSC or PAL footage shot with a video camera) you will most likely want to remove one of the fields, or de-interlace the footage, prior to encoding. Many third-party applications offer this capability within their own interface, but you can also choose this option in the Flash Video Exporter dialog box.
Using the De -interlacing pop-up menu, you can choose to eliminate the upper or lower field. For more information, see the section "Interlaced and Progressive Video
Where can I get more information about the Flash Video file format?
Detailed technical information about the FLV file format is published as part of the SWF specification at www.macromedia.com/software/flash/open/licensing/fileformat/. An open source implementation of the FLV video format is available atffmpeg.sourceforge.net/.What’s the best pixel dimensions for transporting or encoding data based on the H.263 standard?
Would there be any benefits to encoding the video at: 128 x 96, 176 x 144, 352 x 288, 704 x 576, 1408 x 1152?Flash Video supports an extension to H.263 that supports frames with any dimensions. However, there is probably a small benefit to frame sizes that are a multiple of 8 x 8 pixels.
What improvements to video performance have been made with Macromedia Flash Player version 7?
Flash Player 7 increases playback performance for video significantly by allowing full speed playback of much larger and longer video files. Flash Player 7 also adds support for progressive download video, allowing FLV files to be loaded and played back at runtime.
How does Flash Video work with QuickTime?The Flash Video Exporter plug-in (included with Flash MX Professional) enables applications that support QuickTime movies to encode/transcode directly video and audio into the Flash Video (FLV) file format. Additionally, Flash MX and Flash MX Professional 2004 support importing QuickTime movies, which are then encoded into FLV and placed in the Flash Timeline. Flash does not support playing back QuickTime movies, such as those encoded in MPEG2 or MPEG4.Can Flash Player play back Windows Media, QuickTime, or Real video files?
No. Flash Player does not support playback of video files created with other video codecs such as those used in Windows Media Player, Real Player, or QuickTime Player. These files can be transcoded into the Flash Video file format (FLV).
Can I stream Flash Video?
Yes, with Macromedia Flash Communication Server (available separately). See separate FAQ section on Flash Communication Server.
Can I use Flash Video on devices?
Yes, devices that have Flash Player 6 or later support video playback. Earlier versions of Flash Player, including Flash Lite, do not support video playback features.Can I use Flash Video on CD/DVD ROM?
Yes, Flash Video files can be played back from fixed media such as CD-ROM or DVD-ROM. For greater control and enhanced capabilities when using fixed media, consider Macromedia Director MX.
What DRM (Digital Rights Management) features does Flash Video have?
Flash Player does not currently support any Digital Rights Management tools.
Faster start and better buffering: Buffering enables videos to be seen immediately rather than having the end-user wait.Programmable stream control: A server scripting environment enables development of audio and video applications with unprecedented levels of functionality and interactivity.
Distributed data synchronization:
This feature enables developers to create applications that use real-time data such as synchronized close captioning, stock tickers, or multiuser games.
What file formats does Flash Communication Server MX stream? Flash Communication Server MX can stream both FLV and MP3 file formats. What standard is the Audio compression based on?For playback, Flash Player supports MP3, ADPCM, and a proprietary voice codec. For capture, Flash Communication Server MX supports the proprietary voice codec. The voice codec can be licensed from a company called Nellymoser.
How can I send the best video depending on the client connection?Because Flash Communication Server-based applications establish a persistent connection between the client and server, developers can determine the client's connection speed and deliver the most appropriate video. For example, for recorded video, the developer can choose to deliver the video with the bit rate closest to the client’s connection rate. For live video, the developer can choose to alter video stream properties such as video size, frames per second, quality, or bandwidth settings to deliver appropriate video.
How can I send Flash Video most effectively over my network?
Because only bits that are viewed are sent to the client, streaming in itself offers a very effective form of video delivery in terms of network bandwidth. In addition, Flash Communication Server MX also provides for server-to-server stream passing (or splitting) to enable a branch and leaf style cluster to be configured. This way, the same live or recorded video stream can be served up from multiple servers running Flash Communication Server MX on the network so no one machine becomes overburdened. This enables developers to create scalable server configurations to handle large numbers of clients and supports failover and redundancy servers. For more information about how to set up Flash Communication Server MX to support a multiple server environment go to
What kind of capacity backbone is needed for streaming video over the Internet with the Flash Communication Server? The capacity that you need to stream your video broadcast depends on the number of people that will be simultaneously viewing your video and the size of your video stream.You can get a simple estimate of the bandwidth you will need to stream your video by multiplying the number of simultaneous viewers that will be watching your video times the bandwidth at which they will be viewing it.
For example, if your video is being streamed to 4 viewers and each video broadcast is at 200 Kilobits per second (kbps) then the backbone you'll need is 200 kbps x 4 = 800 kbps.
For more information download the white paper on this topic at
Where can I find information about the pricing and different editions of Flash Communication Server? You can find pricing information and edition de tails about Flash Communication Server at
Director MX and Flash VideoWhat additional video capabilities does Macromedia Director MX add to a Flash MX project? Director MX adds the following video capabilities to a Flash MX project:
Full-screen, high performance video in a variety of formats (for example, QuickTime, RealVideo, FLV)Additional Media types (for example, BMP, GIF, and more )Extensibility (device control, custom input devices, and so on)
Interactive real-time 3DHigher performance animation for games and simulations
Fine-grain memory management
Tools for deploying to CD-ROM, DVD-ROM, or kiosks
Where can I find additional information about Macromedia Director MX and Flash MX Professional?
Check out these resources:
On using Flash MX and Director MX together:
On using digital video i n Director:
Other Director tutorials
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