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

[belcampo]

Neil Salstrom wrote:
> 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.
The problem probably is in the misdetection of fields vs. frames. I 
guess it's 50interlaced fields, which is 25fps.
If fields are interpreted as frames you get the slow-motion effect.
I issued 1456 1457 1472 on the ffmpeg 'bug' list.
Depending on the container mp4 mkv or mpeg-ts you probably can 
circumvent the situation by defining 50fps in the container, play at 
double-speed.
>>>
>>> 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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