[mythtv-users] MPEG4 bigger than MPEG2?

Nick Rout nick.rout at gmail.com
Sat Mar 10 20:57:33 UTC 2012

On Sun, Mar 11, 2012 at 9:46 AM, Nick Rout <nick.rout at gmail.com> wrote:
> On Sun, Mar 11, 2012 at 9:39 AM, Ross Boylan
> <RossBoylan at stanfordalumni.org> wrote:
>> On Sat, 2012-03-10 at 14:33 -0500, Raymond Wagner wrote:
>>> On 3/10/2012 13:43, Ross Boylan wrote:
>>> > On Fri, 2012-03-09 at 09:06 -0700, Tom Hayward wrote:
>>> >> On Thu, Mar 8, 2012 at 20:51, Ross Boylan<RossBoylan at stanfordalumni.org>  wrote:
>>> >>> Hi, everyone.  I'm a new user, and am wondering why transcoding is
>>> >>> making my files bigger.  More specifically, I think I have transcoded a
>>> >>> file from MPEG-2 to MPEG-4, and it got a little bigger (3.1 vs 2.9GB).
>>> >> The real question is: Why do you want to transcode?
>>> > To save space.
>>> Most people around here are of the opinion that recordings should only
>>> be transcoded for compatibility with other devices, not to save space.
>> That's useful information.  I do tend to fill up my disks though...
>>> Transcoding is a very CPU intensive prospect, and while CPUs are
>>> continually getting more efficient, hard drives are continually getting
>>> cheaper.  Until the floods last October drove up hard drive prices, an
>>> average HD recording might cost $0.20 of disk space per hour,
>>> or maybe
>>> $0.15 after spending a couple minutes defining a cutlist, and a couple
>>> more running a lossless transcode.  Transcoding to H264 while retaining
>>> quality might drop that to $0.05-$0.07,
>>> but is going to run at a
>>> fraction of real-time, and eat up considerable electrical power doing
>>> so.  When you consider the cost of the increased power consumption as
>>> compared to putting that machine in standby, or even just idling, the
>>> cost benefit all but vanishes.  It's easier, and only modestly more
>>> expensive, to just buy more hard drives.
>> Out of curiosity, where do those cost figures come from?
>> One other factor: additional disks also use more power.
>>> > When editing the transcode options (autodetect MPEG2) does selecting
>>> > "lossless transcoding" do the TS->PS transcode?  The description, e.g.,
>>> > "keep audio and video formats identical to the source", sounds as if it
>>> > will not.  If it does not, how do I get the desired conversion?  The
>>> > only video codes I see are MPEG-4 and RTJpeg.
>>> TS and PS are two different types of MPEG2 containers.  A container is
>>> just a wrapper that contains video, audio, and other sundry data
>>> streams.  Think of it like a 'tar' file.  There is almost no CPU usage
>>> to convert between different containers, as the streams are typically
>>> just copied from one to the other.
>> I have trouble reconciling that statement with Tom Hayword's that
>> "Re-muxing from MPEG2-TS to MPEG2-PS can save up to 20%."  Can anyone
>> clarify?
> simple: different containers have different overhead. TS has more
> overhead than PS. TS is designed so you can start watching anywhere in
> the stream  (eg when you turn the TV on) so presumably contains extra
> timing and sync info so a player/TV can pick up the stream anywhere
> along the way.

According to what I read when googling, TS is also for situations
where there is significant chance of packet loss and has extra error
correction too.

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