[mythtv-users] Transcoding issues. SD is fine, HD fails

Neil Salstrom salstrom at gmail.com
Wed Apr 14 05:59:47 UTC 2010


On Tue, Apr 13, 2010 at 8:59 PM, Jim Stichnoth <stichnot at gmail.com> wrote:
> On Tue, Apr 13, 2010 at 6:35 PM, Neil Salstrom <salstrom at gmail.com> wrote:
>> Is Transcoding broken in 0.23?  I'm running 0.23-fixes (on Debian
>> Lenny) and the other day decided to try and save some space by
>> transcoding some recordings.  I'm using a HDHomerun (at one point
>> Comcast QAM and now OTA).  I transcoded a dozen or so Mythbusters (SD,
>> 480i) and everything was great.  File size was much smaller and the
>> quality was great (this was using the "Autodetect" option).
>>
>> I then went a head and transcoded many more shows (again using
>> autodetect)... This time they were HD (both 720p and 1080i).  Uh oh...
>> Not good!  The video is now slow and juddery and they sound like
>> SLOOOOOWWWWW tape being played.
>>
>> This only happens with HD.  All the Autodetect options are default.
>>
>> I have a feeling I just lost all my Simpsons....
>>
>> Anyone else experience this?  I've never debugged before but if anyone
>> has any suggestions on what I can do to try and figure this out I'm
>> game!
>>
>> Neil
>
> Are you using an ION-based frontend?  Are you transcoding to MPEG4?
> The ION does not do hardware decoding of files created by MPEG4
> transcoding (though the ION 2 supposedly does).  This leaves the
> not-so-powerful Atom CPU to do the decoding.  The Atom is just
> powerful enough to decode SD MPEG4, but not HD.
>
> The same will be true for any under-powered CPU, unless you have ION 2.
>
> Run "top" during playback to see how much CPU is being utilized.
>
> Jim
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>

I guess I should have included more info!

The frontend is an AMD dual core 5200+ cpu with a Nvidia 8400GS
(512MB) using VDPAU.  It's never stuttered with anything I've thrown
at it and on a non-transcoded file the CPU load barely even registers.
 With a transcoded file it's around 20% of one core.

The "Autodetect" profile I'm using creates MPEG-4 files.
Bitrate: 2200Kbps
Maximum quality: 2
Minimum quality: 15
Max quality difference between frames: 3
(checked) scale bitrate for frame size
(checked) enable high quality encoding
Number of threads: 1
(checked) Enable 4MV encoding

Codec: MP3
Sampling rate: 32000
MP3 Quality: 7
Volume: 90%


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