[mythtv] Ticket #12303: mythtranscode destroys audio

Dan Wilga mythtv-dev2 at dwilga-linux1.amherst.edu
Mon Nov 17 14:18:44 UTC 2014


On 11/15/14 6:48 AM, Raymond Wagner wrote:
> On 11/14/2014 7:25 AM, John Pilkington wrote:
>> On 14/11/14 12:26, MythTV" wrote:
>>> #12303: mythtranscode destroys audio
>>
>>>   Would it help to have the two files?
>>>   34M     before.mpg
>>>   76M     after.nuv
>>>
>> It's unlikely to do any harm to put them in a drop-box somewhere...
>> ... but isn't this supposed to be about compression?
>
> If you want to actually perform recompression of your files, instead 
> of simply performing a lossless cut of MPEG2 recordings, you shouldn't 
> use mythtranscode.  You seem to be recompressing to RTJPEG for some 
> reason, but even properly configured, mythtranscode is limited to 
> MPEG4ASP, which is only a modest increase in compressibility over 
> MPEG2, and you're stuck in a NUV container.
I have to disagree with the statement regarding MPEG4 compression using 
mythtranscode. When I record OTA using my HDHR on a 1080i channel, I end 
up with a result that is anywhere from 7.2 to 9.8 Gb/hour. After going 
through mythtranscode to MPEG4, it ends up about 3.2 Gb. Is this optimal 
in terms of size/quality compared to other codecs? Certainly not. But 
it's a roughly 60% savings in disk space that requires much less CPU to 
achieve compared to better codecs like H.264. The tradeoff between CPU 
usage and disk savings is pretty good, IMHO.



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