How to obtain the sound's waveform
After loading a sound inside a player, through the use of
LoadSound,
LoadSoundFromMemory or
LoadTrackFromCd methods, the
Waveform class allows generating a bitmap of the sound's waveform: this bitmap can represent the sound in its full length or, in alternative, one or more portions (also known as "views") of the same sound.
In order to generate one or more bitmaps of the loaded sound, the control needs to analyse the sound's contents: this task is performed through a call to the
Waveform.AnalyzeFullSound method. The analysis can be more or less accurate depending upon the resolution passed to the
nResolution parameter; higher resolutions will allow a better quality because more peaks will be detected: as a side effect, higher resolutions will require more memory and will generate larger bitmaps. The analysis can be aborted at any time through a call to the
Waveform.AnalyzeAbort method.
After calling this method, the control will allow the container application to stay up-to-date about the analysis advancement through the following events:
WaveAnalysisPerc: fired several times during the analysis in order to inform the container application about the percentage of advancement.
WaveAnalysisStop: fired when the sound's analysis is completed: after catching this event, it will be possible requesting to the control the creation of the waveform's bitmap through a call to the Waveform.CreateFileBitmapView and Waveform.CreateMemoryBitmapView methods. It's important to note that this event will report the exact number of peaks detected inside the loaded sound and the exact duration in milliseconds of each peak. When generating the bitmap for the full sound's waveform, the reported number of peaks will be exactly equal to the width in pixels of the bitmap. In case you should create a view of a given sound's range, you could obtain the number of pixels needed to display the waveform's view through a call to the Waveform.GetBitmapViewWidth method.
After having analyzed a certain song, in order to save CPU time when you will load and analyze again the same song, you have the possibility to store analyzed waveform's peaks into a file using the
Waveform.PeaksSave method and to retrieve them at a later time using the
Waveform.PeaksLoad method:
WaveAnalysisStart and
WaveAnalysisStop events will be generated in this case also.
Below you can see five bitmaps generated using the same sound (whose duration is around 2.4 seconds length) but with five different resolutions (just for your information the song used for generating these bitmaps is available on this
link); all these bitmaps have been created using the same height of 100 pixels:
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Resolution passed to AnalyzeFullSound method
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Generated bitmap
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WAVEFORM_RES_MAXIMUM
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WAVEFORM_RES_VERY_HIGH
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WAVEFORM_RES_HIGH
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WAVEFORM_RES_MIDDLE
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WAVEFORM_RES_LOW
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As mentioned before, you can also generate a "view" of a defined portion of the loaded sound: on the bitmap below you can see the original song in its full length (with WAVEFORM_RES_MAXIMUM resolution)
and below you can see the view of the same song for the range between 500 and 1500 milliseconds
On the samples above we have used a very small song limited to 2.4 seconds: in case you should be in need of displaying the full waveform of a longer song on a space much smaller than the total number of required pixels, the
Waveform.CreateFileBitmapView and
Waveform.CreateMemoryBitmapView methods will shrink the waveform in order to fit exactly inside the available space; in the example below you can see a 3 minutes song fitting inside a 455 pixels wide bitmap: the original full length bitmap, using the WAVEFORM_RES_MAXIMUM resolution, would require a width of 243,683 pixels.
VERY IMPORTANT: When using high resolutions and big sound files, keep count that the Windows operating system has limits on the size of bitmaps creation; this means that it would be better avoiding the creation of very large bitmaps: in this case it would be a better approach splitting the total song's bitmap into several smaller bitmaps, for example creating bitmaps whose width in pixels doesn't exceed the current screen width.
For further details about using the embedded Waveform refer to the
Waveform class section.
Samples of waveform management in Visual Basic 6 and Visual C++ 6 can be found inside the following samples installed with the product's setup package:
- BeatsDetection
- Waveform
