[mythtv-users] Transcoded recording got larger!

Jon Bishop jon.the.wise.gdrive at gmail.com
Wed Aug 6 05:56:16 UTC 2008


On Aug 5, 2008, at 10:20 PM, Brad DerManouelian wrote:

> On Aug 5, 2008, at 10:09 PM, lindsay.mathieson wrote:
>
>> I just tested transcoding a 5.3GB HD Recording. All settings
>> are the defaults, the transcoding used the default MPEG2
>> profile. The recording went from 5.3GB to 8GB, isn't it
>> supposed to shrink?
>
> Transcoding a recording doesn't shrink the recording. It transcodes it
> to what you tell it to transcode it to.
> Yes, usually people tell it to transcode to something smaller. You
> apparently didn't.

What he is saying is that you have to modify your transcode settings.  
For me, transcoding an HD MPEG2 OTA stream, I use a xvid codec withga   
bitrate of 2200 and mp3 audio with the highest quality setting (which  
is 1, not 9) and it shrinks my Nova episodes from 5.5gb to between  
600mb and 1.5gb, depending on the video (more motion/changes in  
scenes=more space)

There's also some info in the wiki about this.


>> One possible factor I can think of is its almost certainly a
>> SD program that's been upscaled to HD.
>>
>> What I want to achieve is some fairly large space reduction
>> - I have 20 scrubs recordings I do want to watch but don't
>> have the time now and I need the space for other things. I'm
>> quite happy with the average 1 episode divx files you can
>> D/L off the net and they're typically only 350MB, so I was
>> hoping for something like that.
>
> Try a different profile or modify the profile you used to choose a
> video size that is smaller than the one you're starting with.

All the default transcode profiles, as I understand it, are not  
'ideal' so much, as generic. I would suggest creating a new one, and  
setting all the settings to your desired rates, and try that. It is  
entirely possible to transcode a video to a higher bitrate than is  
needed, this can result in massive files with no change in quality.  
You could even transcode my 1 gig files back up to 5 or 6, just by  
adding to the bitrate. Won't make the picture any better though (might  
make it worse, multiple transcodes do degrade quality)

There's really no 'right' settings. You'll want to keep reducing the  
bitrate until the picture quality is unacceptable, and then increase  
it back to where it worked for you. Everyone's definition of  
acceptable is going to be different.

~Jon



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