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Presentation Context

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The presentation context contains name-value pairs that describe the content requested by a client. There is one context for each client. The following table identifies the context values defined by Windows Media Services.

Name

Value (data type)

Key

Description

WMS_PRESENT_BITRATE

long

11

Contains the maximum bit rate for the streams sent to the client. This value is constant and is determined by the server at the start of the presentation.

WMS_PRESENT_BROADCAST

long

6

Contains a value that specifies whether a presentation is a broadcast. A value of 1 indicates true and 0 indicates false.

WMS_PRESENT_CONTENT_DESCRIPTION

IUnknown*

3

Contains an IUnknown pointer that you can use to retrieve a pointer to an IWMSContentDescriptionList interface. You can call the GetAndQueryIUnknownValue method on the IWMSContext interface to retrieve a pointer to IWMSContentDescriptionList.

WMS_PRESENT_DURATION_HI

long

12

Contains the high-order 32 bits of a 64-bit integer indicating the maximum possible time, in milliseconds, that the presentation can last. This value is only set if the presentation extends beyond approximately 1200 hours.

WMS_PRESENT_DURATION_LO

long

13

Contains the low-order 32 bits of a 64-bit integer indicating the maximum possible time, in milliseconds, that the presentation can last. This value is set for each item in the playlist.

WMS_PRESENT_ORIGINAL_PHYSICAL_NAME

String

16

Contains the content location retrieved after the URL requested by the client is resolved to a publishing point. This is the original local source that is retrieved after expanding a publishing point. This is the physical URL before a Physical URL Transform is performed.

WMS_PRESENT_ORIGINAL_REQUEST_NAME

String

17

Contains the URL requested by the client.

WMS_PRESENT_PHYSICAL_NAME

String

4

Contains the URL for the presentation.

WMS_PRESENT_PLAY_RATE

double

14

Contains the rate at which the presentation is streamed. A value of 1 indicates normal forward speed. A value greater that 1 indicates that the content is being fast-forwarded. A value less than 0 indicates that the content is being rewound. For example, a value of 2 indicates that the content is being fast forwarded at twice the normal rate, and -2 indicates that it is being rewound at twice the normal rate. This value is copied from the WMS_COMMAND_CONTEXT_RATE context value.

WMS_PRESENT_PLAYLIST_ENTRY_ROLE

String

45

Contains the role attribute in a playlist.

WMS_PRESENT_PREROLL_TIME

long

81

Contains the amount of preroll time, in milliseconds, specified in the Windows Media file header for the content. The preroll is initially determined by Windows Media Encoder and represents the amout of content that must exist on the client before the content can be played.

WMS_PRESENT_REDIRECT_LOCATION

String

70

Contains a URL sent by the cache manager in response to NS_E_REDIRECT. For more information, see Implementing Reverse Proxy.

WMS_PRESENT_RELIABLE

long

8

Contains a flag that indicates whether the digital media stream must be carried over a reliable data communications transport mechanism. The value of the flag is 1 for true and 0 for false.

WMS_PRESENT_REQUEST_NAME

String

5

Contains the URL requested by the client.

WMS_PRESENT_SEEKABLE

long

7

Contains a flag that indicates whether the end user can seek to a specific time offset in the digital media stream. The value of the flag is 1 for true and 0 for false. Only on-demand content is seekable.

WMS_PRESENT_START_TIME

QWORD

15

Contains the start time of the presentation. This is the start time of the play request, in milliseconds, as an offset from the beginning of the stream. This might not be present in all play requests.

WMS_PRESENT_STREAM_HEADERS

IUnknown*

2

Contains an IUnknown pointer that you can use to retrieve a pointer to an IWMSStreamHeaderList interface. The IWMSStreamHeaderList interface contains a collection of IWMSStreamHeader objects that describe each item of content in a presentation. You can call the GetAndQueryIUnknownValue method on the IWMSContext interface to retrieve a pointer to IWMSStreamHeaderList.

WMS_PRESENT_TOTAL_BYTES_SENT_HI

long

18

Contains the high-order 32 bits of a 64-bit integer containing the total number of bytes that have been sent to the client.

WMS_PRESENT_TOTAL_BYTES_SENT_LO

long

19

Contains the low-order 32 bits of a 64-bit integer containing the total number of bytes that have been sent to the client.

WMS_PRESENT_TOTAL_PLAY_TIME_HI

long

20

Contains the high-order 32 bits of a 64-bit integer containing the total presentation time, in seconds.

WMS_PRESENT_TOTAL_PLAY_TIME_LO

long

21

Contains the low-order 32 bits of a 64-bit integer containing the total presentation time, in seconds.

WMS_PRESENT_WMSSINK_SELECTED_BITRATE

DWORD

51

Contains the bit rate of the content that is being sent to the client.

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