[mythtv-users] Audio out of sync in Mytharchive generated DVD
Rod Smith
mythtv at rodsbooks.com
Mon Apr 9 22:41:37 UTC 2007
On Monday 09 April 2007 17:38, Chris Weiland wrote:
> I'm trying to archive a few of my recordings to DVD using Mytharchive,
> which worked beautifully, except that the audio was out of sync by about
> 3-5 seconds.
This is a serious problem with every tool I've tried to make DVDs, although
it's worse with some tools and source files than with others. That said, a
3-5 second sync problem is pretty awful. The usual pattern for me is that the
audio sync starts out OK but slowly drifts over the course of the recording.
In any event, I've had better luck using mencoder to create MPEG-2 files from
MPEG-4 and non-Myth sources than using MythArchive's tools (namely ffmpeg). I
still use MythArchive to create the DVD, but not to transcode into MPEG-2
format. Here's the command I use:
mencoder -vf kerndeint,softskip,scale=720:480,harddup -ofps 30000/1001 -aspect
${aspect} -ovc lavc -lavcopts
vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9600:vbitrate=${vbitrate}:keyint=18:turbo:trell:dc=10:autoaspect=1 -oac
lavc -lavcopts acodec=ac3:abitrate=192 -of mpeg -o ${dest} ${src}
Note that's one big long line; it'll be split across multiple lines by the
e-mail transfer. Replace ${aspect} by the source's aspect ratio (1.3333 or
1.7777), ${vbitrate} by your desired bitrate (such as 4771000 to fit two
hours on a 4GB DVD), ${dest} by the destination filename, and ${src} by the
source filename. Of course, I've got this in a script, myself. I'm not yet
100% satisfied with my parameters; I'm still fiddling with them, but it's a
slow process. It's also possible to add a crop option to crop the
letterboxing off of letterboxed NTSC source material.
Once I've transcoded a recording, I use MythArchive with the "always
transcode" option DISABLED and the "don't re-encode" quality setting; the
whole point of using mencoder is to bypass the buggy ffmpeg step.
Nine times out of ten, the DVDs I get from this process have better audio sync
than they do if I'd used MythArchive with its ffmpeg transcoding. I also get
better deinterlacing (due to the kerndeint option) -- MythArchive/ffmpeg
tends to produce hideous interlacing artifacts. I still have occasional
problems with this approach, but they're less common and usually less severe
than what MythArchive/ffmpeg produces.
All of this applies to material that wasn't originally in MPEG-2 form or that
needs processing to reduce its size or otherwise modify it. As I've got two
tuners with hardware MPEG-2 encoders, when I know I'll be making a DVD from
material obtained from them, I prefer to set the recording bitrate
appropriately and then use MythArchive with the "always transcode" option
disabled and the quality set to "don't re-encode". When I do this, though,
I'm sure to set the recording resolution to a DVD-compatible one (typically
720x480).
> The wiki
> article also suggests setting "Always use Transcode", which was on in both
> tries.
I disagree that this is a good idea, at least in my experience. Maybe it helps
with source files recorded with certain hardware and/or software, but not
with the files I've used.
FWIW, I've run across a few instances where my MPEG-2 hardware encoder
produces audio that's about 100-200ms out of sync when played by MythTV, but
when transcoded with mencoder and a DVD created, the audio sync is much
better. Thus, I try not to judge the audio sync until I've got a DVD image on
disk (see below).
> Other than that, I don't really know what to make of it. I don't really
> want to mess around with it until I know what to do because each try takes
> about 2 hours to burn, plus the disk.
Try "burning" to an .iso image rather than directly to disc. You can then move
the .iso file to your Myth Video directory to test it. If it's good, you can
then burn that image to disc:
growisofs -dvd-compat -Z /dev/dvd=mythburn.iso
Replace mythburn.iso with the source filename, if you change it or need to
refer to it by its complete pathname. If you were to do this blindly, it
wouldn't take much longer than telling MythArchive to burn the disc directly.
If you find a problem, though, it'll be quicker and easier to correct when
you do it this way, and you won't waste a disc in the process.
As an alternative to all of this, you could try creating a MythTV native
backup rather than a conventional DVD. This will be quicker and will preserve
the files in their original form, so if audio sync is correct when you play
the recording normally, it should be OK in the DVD you burn, too. The trouble
is that the DVD won't be playable on a standard DVD player; you'll need a
computer capable of playing the files that MythTV records. (It doesn't
necessarily have to be a MythTV system itself, though.)
--
Rod Smith
http://www.rodsbooks.com
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