Kamaelia.Util.RateChunker

• component RateChunker

• Breaks data into chunks matching a required chunk rate
  • Example Usage
  • Behaviour

Breaks data into chunks matching a required chunk rate

Send data, such as binary strings to this component and it will break it down to roughly constant sized chunks, to match a required 'rate' of chunk emission.

This is not about 'real time' chunking of a live data source, but is instead about precisely chunking data that you know has been generated, or will be consumed, at a particular rate.

You specify the 'rate' of the incoming data and the rate you want chunks sent out at. RateChunker will determine what size the chunks need to be, applying dynamic rounding to precisely match the rate without drift over time.

Example Usage

Chunking a stream of 48KHz 16bit stereo audio into 25 chunks per second of audio data (one chunk for each frame of a corresponding piece of 25fps video):

bps = bytesPerSample = 2*2

Pipeline( AudioSource(),
          RateChunker(datarate=48000*bps, quantasize=bps, chunkrate=25),
          ...
        )

The quanta size ensures that the chunks RateChunker sends out always contain a whole number of samples (4 bytes per sample).

Behaviour

At initialisation, specify:

• the rate of the incoming data (eg. bytes/second)
• the required rate of outgoing chunks of data
• the minimum quanta size (see below)

Send slicable data items, such as strings containing binary data to the "inbox" inbox. The same data is sent out of the "outbox" outbox, rechunked to meet the required chunk rate.

The outgoing chunk sizes are dynamically varied to match the required chunk rate as accurately as possible. The quantasize parameter dictates the minimum unit by which the chunksize will be varied.

For example, for 16bit stereo audio data, there are 4 bytes per sample, so a quantasize of 4 should be specified, to make sure samples remain whole.

If a producerFinished or shutdownMicroprocess message is received on the "control" inbox. It is immediately sent on out of the "signal" outbox and the component then immediately terminates.

---

Kamaelia.Util.RateChunker.RateChunker

class RateChunker(Axon.Component.component)

RateChunker(datarate,quantasize,chunkrate) -> new Chunk component.

Alters the chunksize of incoming data to match a desired chunkrate.

Keyword arguments:

• datarate -- rate of the incoming data
• quantasize -- minimum granularity with which the data can be split
• chunkrate -- desired chunk rate

Inboxes

• control : Shutdown signalling
• inbox : Data items

Outboxes

• outbox : Rechunked data items
• signal : Shutdown signalling

Methods defined here

__init__(self, datarate, quantasize, chunkrate)

x.__init__(...) initializes x; see x.__class__.__doc__ for signature

checkShutdown(self)

main(self)

Main loop