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

[John Pilkington]

On 11/12/13 01:42, A. F. Cano wrote:
> On Mon, Dec 09, 2013 at 04:40:29PM +0000, John Pilkington wrote:
>> ...
>> First; why are you recording HD?  Is that the only version that is
>> available to you?
>
> As other people in another part of this thread have pointed out, that
> is the only choice I have.  I use an antenna and the material comes
> in HD.
>
>> Second; it looks as if your transcode isn't working.  Here in the UK
>
> Interestingly, when I tried to transcode manually with the command you
> gave below, mythffmpeg was not installed.  I installed it via aptitude.
> We'll see if this has any effect next time I record a show.
>
>> 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.
>
> It looks like the default parameters cause extreme lossy compression.
>>From 5.2G to 254M just by specifying 960 x 512 (1/2 the height and 1/2
> the width).  Obviously this is not the optimal setup.  I can watch other
> videos full screen (with mplayer) and they look much better even though
> they are of lower resolution.  I'll have to try with the -b:v and -b:a
> parameters.
>
> 254M Dec 10 17:45 2131_20131127030000.mpg
> 5.2G Nov 26 23:00 2131_20131127030000HD.mpg
>
>> 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
>
> This is what I tried:
>
> mythffmpeg -threads auto -v verbose -i 2131_20131127030000HD.mpg -s
> 960x512 -acodec mp2 -ac 2 -aspect 16:9 2131_20131127030000.mpg

I was expecting you to try something with -target ntsc-dvd -s 720x480

I still haven't located current documentation for -target.  It could be 
that most of the other stuff is redundant.  Compare my suggestion with 
these files:

/usr/share/mythtv/mytharchive/encoder_profiles/ffmpeg_dvd_pal.xml
/usr/share/mythtv/mytharchive/encoder_profiles/ffmpeg_dvd_ntsc.xml

... but I think the -r and -copyts lines should be dropped, and I would 
guess that there hasn't been a lot of recent testing.  Experiment on a 
/short/ recording!  The dvd format has an extra navigation stream but I 
don't think that will be a problem for you.  And I don't know how 
tolerant any of this stuff is of recording errors.
>
> Also ran mythcommflag manually, but it finished quickly with an
> error.  It might be because the file was quite corrupted because
> of reception problems.  When I tried to watch it within myth, it
> gave a long list of errors and exited back to the "watch recordings"
> window, which incidentally still says that it's 1080i, so something
> didn't get updated properly.
>
>> 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.
>
> The above transcode took about 2:45 for the 1 hour show.
>
>> 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.
>
> Thanks a bunch.  At least now I can watch the highly pixelated shows
> with mplayer and the slow cpu can keep up.
>
> One other question.  I deleted a test recording from within myth.  It
> says that deleting the show from the list does not remove the file.
> Is there a way to manually remove recordings completely? the mpg file,
> the data that gets stored in the database, etc...  I'm aware that there
> is some expiration time, but since the disk is not full, myth is
> apparently not removing shows.
>
> Thanks.
>
> Augustine