If the Metadata passed to SegmentSpeedProvider is null, then the
SegmentSpeedProvider will always return 1f from getSpeed.
Initializing a SpeedChangingAudioProcessor requires a SpeedProvider.
Once configured,this audioProcessor is always active, so buffers are
passed through it. Because getSpeed is always 1, the processor performs
a no-op, but still has to do a buffer copy for each buffer.
By not initializing the audio processor when metadata is null, this
copy can be skipped and the audio pipeline is more performant.
Note: This change does not affect the multiple media-item case, which
is not supported with speed changes, as per Transformer API
documentation.
PiperOrigin-RevId: 513261811
