[mythtv-users] Audio sync

Marius Bjørnstad pmb at fa2k.net
Sat Dec 8 16:20:47 UTC 2012


Hi,

I'm using mythtv v0.26.0-28-ge3087dd, analogue audio output, "Standard"
video decoder and opengl video renderer. The audio and video are not in
sync. If I set AudioSyncOffset to 150, they are approximately in sync.
This happens with both Pulseaudio and ALSA when using mythfrontend, but
ALSA is layered upon Pulseaudio, I haven't tried straight ALSA. When
playing the recorded file in VLC, it's in sync by default. It has always
been like this, also with older versions of Mythtv. My sound card is an
Asus Xonar ST, but I have tried with another sound card too, with the
same effect. Here is a pulseaudio diagnostic command which shows that it
uses the correct sample rate 48kHz, which I have also configured in
Pulseaudio.

[fa2k at blackhole ~]$ pacmd list-sink-inputs
Welcome to PulseAudio! Use "help" for usage information.
>>> 1 sink input(s) available.
    index: 10
        driver: <protocol-native.c>
        flags: NO_REMIX
        state: RUNNING
        sink: 0 <alsa_output.pci-0000_04_06.0.analog-stereo>
        volume: 0:  24% 1:  24%
                0: -36.82 dB 1: -36.82 dB
                balance 0.00
        muted: no
        current latency: 70.00 ms
        requested latency: 30.00 ms
        sample spec: float32le 2ch 48000Hz
        channel map: front-left,front-right
                     Stereo
        resample method: copy
        module: 12
        client: 24 <MythTV>
        properties:
                media.role = "video"
                media.name = "MythTV playback"
                application.name = "MythTV"
                native-protocol.peer = "UNIX socket client"
                native-protocol.version = "23"
                application.icon_name = "mythtv"
                application.process.id = "18160"
                application.process.user = "fa2k"
                application.process.host = "blackhole.lan.fa2k.net"
                application.process.binary = "mythfrontend"
                application.language = "en_US.UTF-8"
                window.x11.display = ":0"
                application.process.machine_id =
"d06f4c0dd7e4a0f222db45970000000b"
                module-stream-restore.id = "sink-input-by-media-role:video"

It would be much better to have perfect sync by default, so I don't have
to twiddle the sync offset and get it almost right. How can I debug this?

Thanks,
Marius

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