CSourceSeeking.ChangeRate method

Article
07/27/2023

[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The ChangeRate method is called when the playback rate changes.

Syntax

virtual HRESULT ChangeRate() = 0;

Parameters

This method has no parameters.

Return value

Returns an HRESULT value.

Remarks

The CSourceSeeking::SetRate method calls this method, which the derived class must implement. The SetRate method updates the CSourceSeeking::m_dRateSeeking member variable, but does not validate the new value. A rate of zero should always be rejected. Rates less than zero indicate negative playback. Most filters do not support negative rates.

The following example shows a possible implementation:

HRESULT CMyStream::ChangeRate( )
{
    {   // Scope for critical section lock.
        CAutoLock cAutoLockSeeking(CSourceSeeking::m_pLock);
        if( m_dRateSeeking <= 0 ) {
            m_dRateSeeking = 1.0;  // Reset to a reasonable value.
            return E_FAIL;
        }
    }
    UpdateFromSeek();
    return S_OK;
}

Requirements

Requirement	Value
Header	Ctlutil.h (include Streams.h)
Library	Strmbase.lib (retail builds); Strmbasd.lib (debug builds)