[mythtv-users] How to transcode to SD within mythtv - system too slow to play HD

[John Pilkington]

On 09/12/13 03:35, A. F. Cano wrote:
> Hi,
>
> I installed myth 0.26.1+fixes20 from deb-multimedia (deb packages for
> Debian Wheezy).  Combined FE/BE.  I've recorded a few shows, but they
> are in HD and the computer is too slow to play HD, even though the
> display is 1920x1200.  I have selected the options transcode recorded
> shows and the low quality option, but still the recorded files are
> HD-size (5.2G to 6.8G for 1-hour shows) and when I play them (in a
> 1920x1080 window) they look fabulously sharp for a second or two and
> then the cpu can't keep up.
>
> What am I missing/misunderstanding?  I would like myth to convert the
> HD shows to SD after recording them, as happens with commflag.
> Of course I'd rather not lose the commercial detection.  Does this
> mean that the transcoding would have to come first and then the
> commflag applied to the SD file? I'm not too sure how myth does all
> this internally.  If it's not possible to have myth go back to recorded
> shows and do this, how could I transcode them externally, say with
> ffmpeg? so I could watch them with mplayer.  Or would it be possible
> to do an external transcode and then replace the files so that myth
> would use the new ones instead? Can myth then be told to run the commflag
> again?
>
> Thanks for any help/hints that might come my way.  And of course,
> now that I got it working, mythtv is an amazing piece of software.
> Here's a virtual toast to the developers.
>
> Augustine
>

First; why are you recording HD?  Is that the only version that is 
available to you?

Second; it looks as if your transcode isn't working.  Here in the UK a 
good-quality SD recording stripped to just the video and one audio 
channel comes at around 1.4 GB per hour; I can usually get 3 one-hour 
shows onto a DVD, with no re-encoding.

I have done conversion from HD to SD like this:

mythffmpeg -threads 2 -v verbose -i infile.mpg -target pal-dvd -b:v 
6000k -s 720x576 -acodec mp2 -b:a 256k -ac 2 -aspect 16:9 outfile.mpg

and on my 2006-vintage laptop throughput is around 30 fps.  Input 
filesize (all streams) around 3 GB per hour, output filesize around 2 GB 
per hour.

Obviously this may need modifying for location, and maybe omit --threads 
or set it to 1, but it should give you a start if no-one comes up with a 
Myth-based solution.  Rename the input file to xxxHD.mpg, use xxx.mpg as 
output and when done use mythcommflag --rebuild --file xxx.mpg to fix 
the database.

HTH

John P