[mythtv-users] Transcoding SD MPEG2 to H.264---recommendations?

f-myth-users at media.mit.edu f-myth-users at media.mit.edu
Tue Nov 30 06:38:37 UTC 2010


    > Date: Tue, 30 Nov 2010 13:46:15 +1300
    > From: Nick Rout <nick.rout at gmail.com>

    > On Tue, Nov 30, 2010 at 7:54 AM,  <f-myth-users at media.mit.edu> wrote:
    > >    > Date: Mon, 29 Nov 2010 13:19:03 +0000
    > >    > From: "D. R. Newman" <d.r.newman at e-consultation.org>
    > >
    > >    > On 29/11/10 08:52, f-myth-users at media.mit.edu wrote:
    > >
    > >    > > However---the result was unusable.  The activity log was crammed full
    > >    > > of "audio 192 time went backwards 0 ms, dropped 1 frames" and "video
    > >    > > time didn't advance - dropped 1 frames" lines, and about halfway
    > >    > > through the transcode, it suddenly went from claiming it had 20
    > >    > > minutes to go, to done.  (It also said "sync: got 26887 frames, 60691
    > >    > > expected", which might explain a thing or two.)  And the result, as you
    > >    > > might expect, was a jumpy mess.
    > >    > >
    > >    > > I have no idea why this didn't work.
    > >
    > >    > One possibility is that the source file contains lots of errors. I
    > >
    > > I considered that, but c'mon.  It was just a normal PVR-250 recording
    > > from an STB.  It plays just fine.  It seems unlikely that every other
    > > frame (on average) has an error in it.

    > What are you using to play the file?

mplayer.

    > 					 Are you keeping the exact
    > filename that you were transcoding and then expecting myth to play it
    > in place of the recorded programme you started with? That won't work
    > well because the recordedseek table will be up the wop (TM technical
    > term).

    > Again if you are giving it a new name and plonking it in mythvideo, it
    > may need a seektable built.

I'm not playing in Myth at all at the moment, since I'm just testing.
I took a PVR-250 recording that plays perfectly both in mplayer and
when sent to a PVR-350 (yes, really, that's how I still watch those
recordings, though obviously if the transcoding works, I'll switch
to some VDPAU-supporting card that has an S-video output and send
the results back to my interlaced CRT) and ran it through Handbrake
with default options, and with some tweaked options when that failed.

In all cases, I got a file that Handbrake said was missing roughly
(but not exactly) half its frames, and which played maybe 200-500ms at
a time and then jumped discontinuously ahead by about the same amount,
forever.

Either I've got a bad build of Handbrake, or it can't cope with ivtv
files.  (Or maybe only with ivtv files that also have VBI CC data
in them.  Or it's something else dumb that I'm not seeing.)  Files
captured in the same exact way have played without incident for me
that way for years, and on some Windows box as well using whatever
Windows defaults to playing mpeg files with.

I haven't (yet) tried either non-Handbrake transcoding, or running
things through ProjectX first (is it scriptable? last I looked, very
long ago, it looked like it only had a GUI, but I haven't had time to
check back during this discussion)---this was just my initial report
of trying the most-obvious thing and having it blow up for no apparent
reason.

I'm not trying to use VDPAU yet on the mplayer side; in fact, I'm
calling mplayer with zero args besides the input file (in MKV format)
to a GeForce 9500 GT (I think---it's either some other nVidia onboard
video on that machine, or a card I stuck in, but I don't recall and
haven't checked yet) and it's doing fine---it's not complaining that
it's too slow to play the result and dropping frames, or anything like
that.  (It complains it can't open libvdpau, which isn't surprising
because I've put zero effort into configuring VDPAU on that machine
yet, and that its using ffmpeg's libavcodec family.)  Of course, it's
only SD video.  If Handbrake hadn't spewed magabytes of complaints
about dropped frames and magically finished halfway through its
estimated time, I'd suspect the player, but at this point I suspect
the problem is with Handbrake and not playback.


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