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  • Pierre-Louis Bossart's avatar
    ALSA: core: add hooks for audio timestamps · 4eeaaeae
    Pierre-Louis Bossart authored
    ALSA did not provide any direct means to infer the audio time for A/V
    sync and system/audio time correlations (eg. PulseAudio).
    Applications had to track the number of samples read/written and
    add/subtract the number of samples queued in the ring buffer.  This
    accounting led to small errors, typically several samples, due to the
    two-step process.  Computing the audio time in the kernel is more
    direct, as all the information is available in the same routines.
    Also add new .audio_wallclock routine to enable fine-grain synchronization
    between monotonic system time and audio hardware time.
    Using the wallclock, if supported in hardware, allows for a
    much better sub-microsecond precision and a common drift tracking for
    all devices sharing the same wall clock (master clock).
    Signed-off-by: default avatarPierre-Louis Bossart <>
    Signed-off-by: default avatarTakashi Iwai <>