[mythtv-users] Transcoding on a non myth machine

f-myth-users at media.mit.edu f-myth-users at media.mit.edu
Fri Jan 6 02:50:32 UTC 2006

    Date: Thu, 5 Jan 2006 17:29:30 -0500
    From: Steve Adeff <adeffs at gmail.com>

    On Thursday 05 January 2006 17:11, Jay Ung wrote:
    > I was wondering if it iis possible to transcode .nuv to avi on a machine
    > that is not a mythtv machine using nuvexport.    I am a total noob when it
    > comes to transcoding.  I would love to use my home server as the transcode
    > machine.  The mythtv box doesn't really have the horsepower.  But the
    > server is not a backend or have any mythtv stuff installed.  If it is
    > possible to transcode this way, is it possible to cut commercials?
    > Basically what I would love to do is record a program, copy it to the
    > server via cron job, cut commercials, and transcode to xvid, then move it
    > back.  I would love to do this completely automatically.  So am I smoking
    > crack, or is this possible.
    > Thanks,
    > joe

    I believe if you install a slave backend on the machine you can set it up to 
    do all the transcoding. I do my commercial flagging this way right now, but 
    haven't entered the world of transcoding.

You'd sure think this should be possible, but when -I- tried it, by
turning on the transcode-every-recording button in the UI and doing
nothing else fancy (in 18.1, on a combined FE/SBE which NFS-mounted
the recordings from the MBE), I had a number of problems (see traffic
from me from a month or so ago).  In particular:

(a) The SBE's mythtranscode was getting handed myth:// "URLs" instead
of just a pointer into the filesystem, then complained that it didn't
support that mode.  Jobs on the MBE ran fine, but that meant that some
random proportion of them would just error out and die.

(b) It then left all the errors in my job queue for some long period
of time and nobody could figure out how to actually make them go away.
(They appear to have all vanished 8 days (yes, not 7) after erroring,
spontaneously; is there some week-and-a-day timeout somewhere?)  This
was apparent from reading the backend logs, since I've got both
backends and the frontend logging to files to "-v" and have since
about 6 weeks ago.

(c) The resulting transcoded files had -VERY- low audio levels, and I
couldn't find any way of making them at least match the originals.
(My recordings in general -also- have low audio levels, despite
setting ALSA mixer levels high; is there some way of convincing 250's
and 350's to record louder?  I'm comparing to the TV itself and all
the other devices which share the cable feed, none of which have this

Since I'd rather not have to do all my transcoding on the MBE (which
has the majority of the tuners), and since transcoding from MPEG2 to
MPEG4 doesn't preserve the closed-captioning information anyway, I
just gave up on the whole idea of transcoding.  If anyone has any
ideas on how to solve (a) and (c), in particular, I'd appreciate it;
the relevant traffic is on the -users list about a month ago, but it
but there was very little discussion and no resolution.

(I now have tools that allow me to dump the CC info from the MPEG2
file into an ASCII file, so I might reconsider transcoding and then
having mplayer render the CC info from the ASCII while playing the
MPEG4---or figure out a way of regenerating MPEG2 from MPEG4
(preferably, also sucking in the CC data) so I can actually use my
-350's native MPEG2 output, but I'd need a solution to the transcoding
issues above.  It'd sure be nice to take advantage of the space-saving
it would make possible.)

[-Is- there some easy way of reverse-transcoding, e.g., MP4->MP2?
Given that, I could compare the quality of MP2->350, MP2->MP4->350
(using its framebuffer support, which works for me), or MP2->MP4->MP2
and then the 350's native output again; presumably I'd only be doing
this if the quality & time were acceptable and I really wanted native
closed-captioning support, which would require some way to re-embed it
into the new MP2 stream.]

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