[libav-bugs] [Bug 647] New: PulseAudio Simple API exact timestamps

bugzilla at libav.org bugzilla at libav.org
Thu Mar 6 19:41:16 CET 2014


http://bugzilla.libav.org/show_bug.cgi?id=647

           Summary: PulseAudio Simple API exact timestamps
           Product: Libav
           Version: git HEAD
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: Normal
         Component: general
        AssignedTo: bugzilla at libav.org
        ReportedBy: Cassuairtall2035 at gustr.com


ffmpeg and libav are using pulseaudio simple api. Please take a look at:

https://github.com/FFmpeg/FFmpeg/blob/master/libavdevice/pulse.c
https://github.com/libav/libav/blob/master/libavdevice/pulse.c

Unfortunately the audio sample rate is not synchronized to the wallclock.
For live streaming pulseaudio with another device like x11grab this is
quite essential to keep audio and video in sync.


As you can see pulselib starts with 0, while alsalib has current wallclock



ffmpeg -f alsa -i pulse
Input #1, alsa, from 'hw:0,1':
  Duration: N/A, start: 1394023291.824293, bitrate: 1411 kb/s
    Stream #3:0: Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s

ffmpeg -f pulse -i mix.monitor
Input #1, pulse, from 'mix.monitor':
  Duration: N/A, start: 0.069521, bitrate: 1536 kb/s <-- PTS starts at 0
    Stream #2:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s

ffmpeg -f x11grab -s 1280x720 -i :1.0
Input #0, x11grab, from ':1.0':
  Duration: N/A, start: 1394023291.788703, bitrate: 441926 kb/s
    Stream #0:0: Video: rawvideo (RGB[16] / 0x10424752), rgb565le, 1280x720,
441926 kb/s, 29.97 tbr, 1000k tbn, 29.97 tbc

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