| 1. | What is progressive download? |
| Answer: | Progressive download enables you to view streaming content as it is downloaded to your media player. With progressive downloads, you can watch live events as they take place. In addition, you do not have to wait for an on-demand stream to download before viewing it. The player delays displaying the content for a few seconds to create a content buffer in order to alleviate packet jitter. |
| 2. | What are the three major streaming media vendors? |
| Answer: | Windows, RealNetworks, and Apple are the three major streaming media vendors. |
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| 3. | What is the purpose of a streaming meta-file? |
| Answer: | Instead of embedding the URLs of the media files directly into your HTML, you can point your users to the URL that houses the meta-file. The media player uses the metafile to synchronize the different clips of your presentation. The media player can then request the session description file for each stream specified in the meta-file. |
| 4. | What is the relationship between "streaming containers," "codecs," "FourCCs," and "RTPUDP"? |
| Answer: | You package streaming media into streaming container files before transmitting over the network. Codecs are algorithms used to encode and decode streaming media, such as MPEG, H.323, and G.711, before transmitting over the network. FourCCs are codes used to identify vendors, such as DivX, that implement the available codec algorithms. RTP is the application layer protocol, and UDP is the transport protocol that the application uses to deliver the streaming media over the network to requesting clients. |
| 5. | What is the difference between the way Apple/MPEG and Windows/RealMedia structure their container files? |
| Answer: | Windows/RealMedia structure their container files into data packets and synchronize the streams by interleaving the data packets within the file itself. Apple/MPEG leave the streams intact and use hint tracks stored within the file to synchronize the streams upon transmission. Therefore, when an Apple/MPEG4 server sends packets over the network, there is no Apple QuickTime- or MPEG4-related information embedded in the packets, just the standard application transport header and payload format information. |
| 6. | Does RTP provide sequence numbers to reorder out-of-sequence packets? |
| Answer: | No. RTP sequences packets in order to detect and drop out-of-sequence packets. Reordering packets would result in too much delay between the sender and receiver. |
| 7. | What is the difference between RTCP and RTSP? |
| Answer: | RTCP is the sister protocol of RTP. RTCP groups and synchronizes the RTP-UDP streams within an RTP session. In contrast, clients use RTSP to instruct streaming servers to play, pause, rewind, and fast-forward streaming media. |
| 8. | What port numbers does RTP use? What about RTSP, WMT, and ReaMedia? |
| Answer: | RTP uses the RTP UDP port range 1638432767. RTP uses the even numbers in this range; RTCP uses odd numbers within the range. RTSP uses TCP port 554. RealMedia also uses RTSP port 554 on TCP for control and synchronization and uses RTP for data transmission. WMT uses MMS on UDP/TCP port 1755 for control and UDP ports 10245000 for data. |
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| 9. | What is the purpose of streaming media session description files? How do they differ from meta-files? |
| Answer: | You can use session description languages to inform requesting clients of the session that they desire to participate in. This way, your users need know only the URL of the session beforehand to participate in the session, not the container file formats, IP addresses, ports, and transport protocols. A web server supplies the client browser with a meta-file to hide from the browser the information that is specific to the media-player specific information. The browser passes the meta-file to the player, and the player requests the session description file for each stream within the meta-file. Note that you can use SMIL for both meta-files and for session description files. |
