[mythtv-users] Mythexport sssssllllllloooooooowwwwww

Chris Kapp chris.kapp at gmail.com
Wed Sep 1 09:31:54 UTC 2010


On Wed, Sep 1, 2010 at 4:14 AM, Diego Torres <torres.diego at ttcpl.com.au>wrote:

> Thanks mate, that was it... sort of.
>
> I added '-threads 0'  and that made all four cores to be utilized.
> At first I realized that there is a "multiple threading" checkbox on myth
> export and used
> that . But it adds '-threads 2' to the command so it only uses two cores.
>
> With '-threads 0' on both passes it only took 1.5 hours for the first pass
> and 1 hour to for the second pass.
> Still not as fast as Airvideo but a heck of a lot faster than before.
>
> The only things I noticed are:
> - The 1 GB RAM was being used with the SWAP going to 200MB or so. I upped
> the memory to 2GB and it still used it all but did not use swap.
> - Even though all 4 cores are being used, none are used more than 80% and
> there is always one that
> oscillates between 30 and 80%. With Airvideo all 4 cores are pretty much
> pegged at 80% the whole time.
> - I am  guessing that the CPU does not go to 100% because of I/O
> bottlenecks. It could be that the 500GB IDE HDD /controller combo
> just can't keep up with ffmpeg using all four cores.
> - The output file is twice as big as Airvideo's so there is definetely a
> mismatch on the settings. I need to investigate that.
> - I realized that myth export uses a two pass approach whilst Airvideo uses
> a one pass approach
> (because the output file starts to fill up immediately).  Doing some
> reading on the ffmpeg lit it says that a two pass
> approach is required with a Variable Bit Rate and in general is recommended
> for quality output.
> I reckon the quality from airvideo's one pass is more than good for the
> ipad so I will try hacking the script (time permittiing) to do a one pass
> only
> and compare the conversion time.
>
>
>
>
The file size difference is likely the version of ffmpeg and x264 that you
are using.  I looked at airvideo earlier in the year and found the
difference in file size as well.  When I followed Fakeoutdoorsmen's tutorial
on building your own ffmpeg, the file sizes shrank to the same size as
airvideo.

http://ubuntuforums.org/showthread.php?t=786095

These are the ffmpeg settings I am using:
ffmpegArgs=" -acodec libfaac -ab 128k -s 320x240 -vcodec libx264 -vpre slow
-vpre ipod320  -threads 0 -f ipod"

Good luck.
Chris.
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