[mythtv-users] MPEG4 bigger than MPEG2?

[Nick Rout]

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.