[mythtvnz] DNLA/UPnP server

[Stephen Worthington]

On Tue, 08 Dec 2009 19:04:46 +1300, you wrote:

>---- Original Message ----- 
>From: Ross and Jemima Knudsen
>To: stephen at jsw.gen.nz ; MythTV in NZ
>Sent: Tuesday, December 08, 2009 4:58 PM
>Subject: Re: [mythtvnz] DNLA/UPnP server
>
>2009/12/8 Stephen Worthington <stephen_agent at jsw.gen.nz>
>
>On Tue, 8 Dec 2009 13:25:00 +1300, you wrote:
>
>> Just to add my 2c.  Do the Sony Bravias you tested on have in-built
>>freeview decoders?  If they do (like the ones now coming on the market)
>>wouldn't they have to be able to be able to decode mpeg2 container and H.264
>>streams that are currently broadcast on FreeviewHD (including the
>>LATM-AAC)?  Or are they not able to tune all Freeview channels?
>
>
>>Almost all LCD TVs now on sale have FreeviewHD tuners, and the Sony
>V5500 models all do.  So they can play what comes off the air.  But
>the transport stream format that MythTV uses to store that data is
>something they do not support, unfortunately.
>
>>But if its being streamed by the Myth box surely it must be possible to convert it back (losslessly) into the original format it 
>>was received in and the TV should have the hardware/software to play it if it can play natively from the signal received?
>
>
>Interesting discussion and progress.
>
>If the Sony Freeview tuners in the V and W series use the standard broadcast stream then perhaps the stream that is filtered out of 
>the hhdhomeruns might also be played by the Sony TV's?
>
>However the hdhomerun streams in .ts format and based on what's been said already the TV's are unlikely to play a native hdhomerun 
>.ts stream either?  (Maybe some can test?)
>
>This implies to me these Sony TVs also convert the live TV transmission into AVCHD before they play it.  (I am not clear on the 
>difference however it seems there is one!)
>
>Following this logic for the TV to natively play the standard mythtv stream, it would have to (in simple terms) go in via the 
>antennae - and not via ethernet - where it needs to be in AVCHD form.

I think people are mixing up the broadcast transport stream format
with file formats.  The broadcast transport stream is a multiplex with
multiple TV channels in it.  Each of the TV channels also has multiple
streams: 1 H.264 video, 1 LATM AAC audio and possibly 1 AC3 audio, and
possibly a teletext stream.  And MHEG5 EPG and EIT now/next EPG as
well - I have not seen documentation on how MHEG5 and EIT are
broadcast but I think they are probably also just streams too.  When
MythTV selects out a channel, it takes those streams it needs from the
ones for that channel and drops the rest of the streams for that
channel and also all other streams for the other channels.  For
example, all MHEG5 data is currently dropped as MythTV does not
support it.  It then multiplexes the streams it wants for that channel
together into a container format and writes that to disk.  The
container format it uses is not the AVCHD format.  It probably uses
188 byte packets, which, I believe, is what is broadcast, as that
would be the simplest thing to do - just copy what was broadcast.  The
AVCHD file format uses 192 byte packets, and does not permit AAC audio
(only AC3 or PCM).

So the problem is the container format - Sony TVs strictly require
AVCHD format for the files they read.  Other TVs, eg Samsung, seem to
support a wider range of transport stream format files and can read
the MythTV format.  This is just Sony being silly really - they could
easily have supported more formats, and could easily release updated
firmware to do just that (the TV's firmware can be updated from a USB
stick).  But Sony invented the AVCHD format, and use it on all their
video gear, so making their TVs only support AVCHD means it is more
likely you will buy a Sony video camera to go with it.

>What does a DLNA TV offer ahead of a mythtv frontend?  The only thing I can see is that it lacks the mythtv frontend hardware - and 
>also a heap of functionality that Sony have not brought anything to my attention to say that the DLNA functionality is going to 
>increase much in the medium term.  That is to say it seems a mythtv frontend is going to be superior for some time to come, and the 
>limits of these FE's are mostly related to the CPU and secondarily the video card also. 

The advantage of a DLNA TV is not having to have another frontend PC -
a considerable cost saving if you already have had to pay for a new
TV.  In my case, it also prevents my mother from accidentally deleting
something I still want to watch, or causing some other disaster.  She
is a complete technophobe, and is able to cause completely
unanticipated disasters with any new technology.

Basically, a DLNA TV can only play back files, it can not do anything
else you normally use a frontend for.  So it is only of use in
specialised cases.  I just happen to have one of those cases.