[mythtv-users] Very low audio level after transcoding

f-myth-users at media.mit.edu f-myth-users at media.mit.edu
Wed Dec 7 22:58:10 EST 2005

[Should I move this to the -dev list?  This seems like a bug, and
nobody here has said anything about it yet....  I'll move it to -dev
and/or just open up a ticket if I don't hear anything.]

Note:  I found the "Volume %" slider in Transcode->MPEG2->Audio Quality
and changed it from 90% to 100%.  It -might- have made a slight difference;
it'll be hard to tell without more testing.  But it certainly didn't make 
-enough- of a difference.

Also:  the self-documentation for that slider claims "Recording volume
of the capture card".  Is that -really- what it's there for?  If so,
why?  In that case, since my capture card is at 90%, it seems that
setting the slider to 100% might be going in the wrong direction, and
maybe I should lie to it and say, e.g., that my capture card was at
50% so transcoding might boost the volume.  But this is backwards and
certainly not how -I- would design the control---how's it -really-
supposed to work?


    Date: Wed, 7 Dec 2005 02:06:39 -0500 (EST)
    From: f-myth-users at media.mit.edu

    In 0.18.1:

    I'm experimenting with transcoding from MPEG2 to MPEG4, and have
    discovered that the transcoded files have very low audio levels;
    I'd guess on the order of 6-9dB down from the source, at least.

    Where are these levels specified?  I'm quite surprised that they're
    affected at all.

    I'm using all the defaults (as far as I know) except that I changed
    the transcoding dimensions from 480x480 to 720x480 to match the
    original from the PVR-250.

    I can verify absolutely that it's the transcoding process that's doing
    this, because I'm saving the originals.  If I play the transcoded
    file, and then rename that file to some temporary name and rename the
    .nuv.old file in place of the original and play -that-, audio is back
    at its normal level.  If I undo the renaming, audio is again quiet.
    This is true for transcodings from 5 different channels.

    According to ps, the actual transcoding process was something like:

    mythtranscode -V 4099 -c 1002 -s 2005-12-06T21:35:00 -p autodetect -d

More information about the mythtv-users mailing list