Programming Flash Communication Server

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Chapter 5: Managing Streams

Stop-motion video can be done in a similar way. Instead of using setInterval( ) to

capture a frame at regular intervals, a single frame can be captured and appended to

the recorded stream whenever a button is clicked. Unlike normal video capture,

every frame in a time-lapse or stop-motion video stream is a complete frame (a video

keyframe, not a so-called difference frame that contains only the delta between two

successive frames). Time-lapse and stop-motion videos will normally require much

more bandwidth than regular video and should be buffered accordingly. Each appli-

cation is likely to be different, but you should try experimenting with a buffer 10

times larger than you might otherwise have used.

Playing Streams in Detail

The NetStream.play( ) method can be used to play live and recorded streams, seg-

ments of recorded streams, and a playlist of streams. The play( ) method has a num-

ber of optional parameters that make this possible:

in_ns.play(streamURI | false, [, start [,length [, flushPlaylists]]]);

The first parameter is required and must be either a relative URI that identifies the

stream to play or the value

false, which stops the current stream from playing. The

remaining parameters, shown inside square brackets, are optional. The nesting of the

square brackets indicates that if one optional parameter is included, then so must all

previous ones. For example, to use the

length parameter, the start parameter must

also be provided.

Playing Live or Recorded Streams

The start parameter can be used to indicate more than its name implies. The possi-

ble values for

start are:

-2

Plays the live stream at the specified URI or plays the recorded stream at that

location if the live stream is not found. If a recorded stream is also not found, the

NetStream object waits for the stream to be published.

-1

Plays only a live stream at the specified URI. If a live stream is not found, the

NetStream object waits for one to be published. A recorded stream at the same

URI will not be played.

0

Plays only a recorded stream at the specified URI from its beginning. If a

recorded stream is not found, an information object is returned to NetStream.

onStatus( ).

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Playing Streams in Detail

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Greater than 0

Same as passing 0, but indicates how many seconds into the recorded stream to

begin playing.

If a

start value is not passed into the play( ) method, the default is -2 (plays a live or

recorded stream).

The

length parameter defines how many seconds the live or recorded stream should

play. For example, to play a stream beginning 1 minute into the stream for 30 sec-

onds, call play( ) as follows:

in_ns = new NetStream(nc);

in_ns.play("announcements", 60, 30);

If the length parameter is -1 or omitted, the stream plays until it ends. Note that, by

definition, live streams always start playing at the current time; only recorded

streams can be started at some offset. But the length of time to play a stream can be

limited even for live streams by specifying a time limit with the

length parameter.

Creating playlists

By default, invoking play( ) overrides any previous play( ) command for that Net-

Stream object, closing the previous stream immediately and playing the new stream.

However, you can create a playlist in which the server treats a sequence of recorded

streams as a continuous stream; the server provides seamless buffering so that there

are no interruptions when the source stream changes.

To add a stream to a playlist, pass

false as the fourth, optional parameter

(

flushPlaylists) when invoking play( ). This tells FlashCom not to close the previ-

ous stream. Instead, the stream is queued and buffered to play after the streams

already in the playlist. Here is a short example. Note that if

flushPlaylists is speci-

fied as

true or omitted, as shown in the first play( ) invocation, FlashCom reinitial-

izes the playlist:

in_ns = new NetStream(nc);

in_ns.play("announcements", 60, 30);

in_ns.play("live_Camera_1", -1, 15, false);

in_ns.play("live_Camera_2", -1, 15, false);

in_ns.play("prod_trailer", 0, -1, false);

The preceding code creates a playlist that plays the following sequence:

1. 30 seconds of the recorded stream named announcements, starting 60 seconds

into the stream

2. 15 seconds of the live_Camera_1 stream

3. 15 seconds of the live_Camera_2 stream

4. The entire recorded prod_trailer stream

The

flushPlaylists parameter can also be used to control how ActionScript data is

streamed. See the “Stream logs” section later in this chapter.