No audio on playback

MythTV
2007-01-23
2013-06-03
  • Kevin Crowston

    Kevin Crowston - 2007-01-23

    I am having a problem playing some MPEG2s on my MVPMC: some play back without sound but others play with no problems (i.e., I know that sound does work, just not with some MPEGs). The same MPEGs both play fine on my desktop machine (e.g., using VLC), and I can't seem to find any difference between them with my limited diagnostic tools. I originally noticed this problem playing via MythTV (the MPEG2s are originally MythTV recordings, and something changed that killed the audio), but it happens also if I play directly from the filesystem.

    I'm using the most recent nightly build, but the problem also occurs using earlier versions, e.g., 0.3.1.

    I've put short (5M) snippets that illustrate the problem on my webserver:  http://kevin.crowston.net/good.mpg plays fine and http://kevin.crowston.net/bad.mpg plays but with no audio.

    I searched the list archives and saw one or two people with similar symptoms, though not exactly: for example, one suggestion was to check that the right audio stream was being played, but these MPEGs have only one audio stream, which is selected. One other person seemed to have exactly the same problem, but no one had answered him.

    Thinking that it might be a limitation of bandwidth, I tried recoding the bad MPEGs with a lower bit rate, but that didn't do anything. Interestingly, when I tried demuxing the MPEGs and remuxing them, the one with the bad audio got an error, so I suspect it's something wrong with the audio--though I have no idea what that might be (the information for the two audio streams says exactly the same thing).

    So, I'm hoping for some help or advice about how to make playable MPEGs....

    Kevin Crowston

     
    • Rick Stuart

      Rick Stuart - 2007-05-20

      Same question I just asked someone else - are you using NTSC or ATSC in your MythTV box? (or what ever it's called in Europe).  One possible problem is that you are recording digital audio (i.e dolby digital).  Mvpmc / MediaMVP doesn't deal with that well.  Martin just added support for it in the file browser (not in the MythTV part of mvpmc) - but we already know there isn't a way to keep the "digital" audio and video in sync w/each other.  Again, it would be nice if MythTV would automatically handle transcoding based on the client's abilities.  That would solve a lot of problems.  I think this is what SageTV does w/the same MediaMVP hardware.

       

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