View source for On-Demand Loading

[http://manual.audacityteam.org/index.php?title=On-Demand_Loading/nl http://manual.audacityteam.org/images/4/45/Flag_of_Holland_small.png]
<div class="intro">With normal file import, you must wait for a progress dialog to complete while Audacity computes the waveform. This can take several minutes with very long uncompressed files like '''''[[Glossary#WAV|WAV]]'''''. When "On-Demand Loading" is enabled in [[Import / Export Preferences|Preferences]], you can play, edit and view the audio almost immediately from any chosen point, while the waveform image is still being computed in the background.</div> 

==Usage==

To use On-Demand Loading, go to the <span class="menu">[[Import / Export Preferences|Import / Export]]</span> tab of <span class="menu">[[Preferences]]</span>, and in the '''"When importing audio files"''' section, check '''"Read uncompressed audio files directly from the original"''':
:[[Image:EnableOD.png|Read files directly in preferences to enable On-Demand]]  


Then import an uncompressed file, for example WAV or AIFF, via any means (drag-and-drop, <span class="menu">[[File Menu|File]] > [[File Menu#Open...|Open...]]</span> or <span class="menu">[[File Menu|File]] > [[File Menu#Import|Import]] > Audio...</span>). A sequence of patterned blocks representing the uncomputed waveform appears at once. The blocks are then progressively replaced from left to right by the computed waveform. To change the point from which the waveform should be computed, click at the leftmost point from which you want the waveform drawn. In the below image, we clicked in the center of the track and after a second or two, the waveform now starts being drawn rightwards from the cursor point: 
[[Image:ODinprogress.png|On-Demand loading moved to center of track]]


Once the computation point has reached the end of the track, any uncomputed waveform will be drawn from right to left, unless interrupted by clicking elsewhere at an uncomputed point.     

<div class="note">Multiple files may be imported simultaneously, and the waveform computation point moved from one to the other by clicking in the required track.  </div>  

The percentage of the waveform that has been computed is displayed on the Status Bar, as shown at bottom left of the image above. When multiple files are being imported, the Status Bar will display the ''overall'' percentage of the multiple tracks that has been computed. To make Status Bar display the percentage completion of a particular track, move the mouse over that track.     

In the future we hope to extend On-Demand processing to compressed formats such as FLAC and MP3, to formats imported via the optional [[FAQ:Installation and Plug-Ins#How do I download and install the FFmpeg Import/Export Library?|FFmpeg library]], and to effects.