[mythtv-users] Share your transcode settings!

Jeremy Jones jeremy.dwain.jones at gmail.com
Wed Jan 11 17:13:08 UTC 2012


On Wed, Jan 11, 2012 at 10:26 AM, Josh Rosenberg <mythtv at desh.info> wrote:

> All,
>
> I'm still struggling a lot with setting up transcoding.  But rather
> than ask for specific help, I'm going to try a different approach.
>
> Those of you who do any sort of lossy or format-converting transcoding
> beyond just stripping commercials, share how you do it!  Built-in
> transcoding, a user job, or what?


I am transcoding to mpeg-2 standard definition (480p) from High Definition
content.  This cannot be done with built-in transcoders, because anything
that changes the resolution makes the container a nuv (nupple Video file).
 So I asked a similar question.  you can find the thread by googling,
"mythtv Replacing mythtranscode command with a custom script".   But to
make a long thread short, I ended up using the "transcode wrapper stub"
from the wiki http://www.mythtv.org/wiki/Transcode_wrapper_stub, which will
take care of replacing the original file and everything for you after
transcoding.  The stub just needs your transcode command added to it.  I'll
post mine tonight as a follow up to this thread, but until then there is at
least one example called, " Low Quality Transcode" on the wiki
http://www.mythtv.org/wiki/Low_Quality_Transcode.

If you use a script someone posted
> online, have you modified it?  If you use a standard utility like
> ffmpeg,


I am using ffmpeg from within the stub.


> or a script with multiple modes, what options do you call it
> with?


No multiple modes in mine.  I call mine by replacing the built-in
transcoder, but it can be run as a user job.  I chose to replace it, so
that I could have the transcodeing run before commercial flagging.


Also, how long does the conversion take and how well does it
> work for you (that is, how much space does it save and how is the
> quality impacted)?
>

Saves a lot of space, but yes quality is impacted, since I am actually
changing (for compatibility with a network player) to Standard Definition
instead of High Definition.  Regardless of that, I would still recommend
using Raymonds wrapper for whatever your setting are.  Other posters may
have more fitting information on ffmpeg settings. (or mencoder, or
handbrake)  It just need to be able to be executed from a cli for the stub
to use it.


> Bonus points for explaining why you chose what you chose, or what
> alternatives you've discarded along the way.
>

I chose to use ffmpeg because I already had it and it seems to be very
popular.  I just google for settings that other users had and tried
different variations until I got output that worked with my network player.
 Once I had that I wrote a script and called it as a user job.  I had
problems though swapping out the files.  The end result had the mythtv file
and the transcoded one.  I had something that was working, but it was not
consistent and actually returned errors in mythtv.  Then I discovered the
wrapper stub, and it made everything easier.  I just abandoned my script
and put my ffmpeg command into that new script and ran it as the user job.

Then I discovered that the commercial skip wasn't working and so I
asked questions here. Turns out the commercial flags are frame specific and
if your transcoding changes frames, then the flags are no good.  So I now
had to run a second user job to flag the commercials.  In getting help on
setting that up someone pointed me to actually changing the mythtv
transcode  command.  I posted asking fo help doing that.  See the thread
starting here:
http://www.gossamer-threads.com/lists/mythtv/users/490927?do=post_view_threaded#490927

>
> Google searching for transcode help seems to mostly reveal people who
> are struggling, and I'd like to hear some examples from people who are
> succeeding!  Regardless of whether your use case exactly matches mine
> or not.
>
> Thanks!
>
> Josh
>
> Like I said, I will post my entire script tonight when I have access to my
computer.

Jeremy
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