Mailing List Archive

On 07/03/15 11:45, Paulgir wrote:
>
> I see the Freeview DVB-T EPG now has 8 days of data included.
> Up until now I have been using http://epg.org.nz data.
> If I want to use the over-the-air guide,can I just check the "use on
> air eit" boxes in Myth Backend set up and disable the running of
> tv_grab_nz-py ? or is there other set up necessary?
>
> Paul
>
Interesting. If I feel the urge I will investigate further. But I am
also somewhat disturbed by related things I have just read regarding
what TVNZ and the BBC are doing. Here is a quote from the "Metadata"
section at http://en.wikipedia.org/wiki/Freeview_%28New_Zealand%29.

"During the third week of December 2014, TVNZ tested using the same
Huffman look-up tables the BBC implemented to force viewers to use
approved Freeview receivers that restrict HD recording and viewing. The
Huffman tables are being used to compress the EIT text used for
terrestrial schedule event names and descriptions. From March 2015, TVNZ
began compressing the EIT schedule again. Compressing the EIT text in
the schedule would not achieve the same receiver use given the
terrestrial EIT only has limited programme details. Receivers that don't
use the BBC huffman tables will either display no details or display
garbage characters."

If TVNZ is really compressing the EIT using Huffman coding then the
MythTV EIT decoding code must be pretty clever to decompress it without
access to the Huffman lookup table(s). (Unless the Huffman table is
embedded in the EIT data in some standard way maybe?)

After reading about how the BBC got OFCOM approval to implement "content
protection" for their HD service and some of the interweb comments about
how this could affect MythTV users I am nervous about TVNZ's plans. As
the paragraph above from Wikipedia says you can't decompress data that
has been compressed with Huffman coding unless you know the Huffman
decoding tree/lookup table. If TVNZ (and others?) follow the BBC path
and compress the EPG and require users to get a licenced copy of the
Huffman table then we'll lose our relatively simple access to the EPG
over the air.

Also it could be the thin end of the wedge heading towards encryption of
"premium" content although I don't see why this would be allowed on
Freeview. But given what OFCOM allowed the BBC to do you never know what
warped reasoning might allow Freeview content to be encrypted.

Hopefully my fears are completely ungrounded and we can continue on our
merry, open source way with our EPG and recording working fine.

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On Sat, 07 Mar 2015 11:45:45 +1300, you wrote:

>
>I see the Freeview DVB-T EPG now has 8 days of data included.
>Up until now I have been using http://epg.org.nz data.
>If I want to use the over-the-air guide,can I just check the "use on air
>eit" boxes in Myth Backend set up and disable the running of tv_grab_nz-py
>? or is there other set up necessary?
>
>Paul

You could do that, but you would lose the benefit of the
post-processing that epg.org.nz does on the EPG data. For example, it
automatically removes "All New" from the front of programme names so
you do not miss the new series when the idiotic EPG producers add
that.

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On Sat, 07 Mar 2015 17:07:54 +1300, Stephen Worthington
<stephen_agent@jsw.gen.nz> wrote:

> On Sat, 07 Mar 2015 11:45:45 +1300, you wrote:
>
>>
>> I see the Freeview DVB-T EPG now has 8 days of data included.
>> Up until now I have been using http://epg.org.nz data.
>> If I want to use the over-the-air guide,can I just check the "use on air
>> eit" boxes in Myth Backend set up and disable the running of
>> tv_grab_nz-py
>> ? or is there other set up necessary?
>>
>> Paul
>
> You could do that, but you would lose the benefit of the
> post-processing that epg.org.nz does on the EPG data. For example, it
> automatically removes "All New" from the front of programme names so
> you do not miss the new series when the idiotic EPG producers add
> that.
>

I wasn't aware that epg.org.nz did that.I will probably leave it the way
it is.
Thanks

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On Sat, March 7, 2015 12:48 pm, David Moore wrote:
> On 07/03/15 11:45, Paulgir wrote:
>>
>> I see the Freeview DVB-T EPG now has 8 days of data included.
>> Up until now I have been using http://epg.org.nz data.
>> If I want to use the over-the-air guide,can I just check the "use on
>> air eit" boxes in Myth Backend set up and disable the running of
>> tv_grab_nz-py ? or is there other set up necessary?
>>
>> Paul
>>
> Interesting. If I feel the urge I will investigate further. But I am
> also somewhat disturbed by related things I have just read regarding
> what TVNZ and the BBC are doing. Here is a quote from the "Metadata"
> section at http://en.wikipedia.org/wiki/Freeview_%28New_Zealand%29.
>
> "During the third week of December 2014, TVNZ tested using the same
> Huffman look-up tables the BBC implemented to force viewers to use
> approved Freeview receivers that restrict HD recording and viewing. The
> Huffman tables are being used to compress the EIT text used for
> terrestrial schedule event names and descriptions. From March 2015, TVNZ
> began compressing the EIT schedule again. Compressing the EIT text in
> the schedule would not achieve the same receiver use given the
> terrestrial EIT only has limited programme details. Receivers that don't
> use the BBC huffman tables will either display no details or display
> garbage characters."
>
> If TVNZ is really compressing the EIT using Huffman coding then the
> MythTV EIT decoding code must be pretty clever to decompress it without
> access to the Huffman lookup table(s). (Unless the Huffman table is
> embedded in the EIT data in some standard way maybe?)
>
> After reading about how the BBC got OFCOM approval to implement "content
> protection" for their HD service and some of the interweb comments about
> how this could affect MythTV users I am nervous about TVNZ's plans. As
> the paragraph above from Wikipedia says you can't decompress data that
> has been compressed with Huffman coding unless you know the Huffman
> decoding tree/lookup table. If TVNZ (and others?) follow the BBC path
> and compress the EPG and require users to get a licenced copy of the
> Huffman table then we'll lose our relatively simple access to the EPG
> over the air.
>
> Also it could be the thin end of the wedge heading towards encryption of
> "premium" content although I don't see why this would be allowed on
> Freeview. But given what OFCOM allowed the BBC to do you never know what
> warped reasoning might allow Freeview content to be encrypted.
>
> Hopefully my fears are completely ungrounded and we can continue on our
> merry, open source way with our EPG and recording working fine.

If they are using the same table as FreeSat this has already been
implemented in MythTV

https://code.mythtv.org/trac/ticket/6498#no1

It would be interesting to see of epgsnoop could be updated to include the
huffman tables.

Looks like another EIT grabber already has the huffman support merged from
MythTV.
- https://github.com/ubaldus/tv_grab_dvb_plus



--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email - steven@openmedia.co.nz
website - http://www.openmedia.co.nz

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On Mon, June 8, 2015 2:07 pm, Steven Ellis wrote:
>
> On Sat, March 7, 2015 12:48 pm, David Moore wrote:
>> On 07/03/15 11:45, Paulgir wrote:
>>>
>>> I see the Freeview DVB-T EPG now has 8 days of data included.
>>> Up until now I have been using http://epg.org.nz data.
>>> If I want to use the over-the-air guide,can I just check the "use on
>>> air eit" boxes in Myth Backend set up and disable the running of
>>> tv_grab_nz-py ? or is there other set up necessary?
>>>
>>> Paul
>>>
>> Interesting. If I feel the urge I will investigate further. But I am
>> also somewhat disturbed by related things I have just read regarding
>> what TVNZ and the BBC are doing. Here is a quote from the "Metadata"
>> section at http://en.wikipedia.org/wiki/Freeview_%28New_Zealand%29.
>>
>> "During the third week of December 2014, TVNZ tested using the same
>> Huffman look-up tables the BBC implemented to force viewers to use
>> approved Freeview receivers that restrict HD recording and viewing. The
>> Huffman tables are being used to compress the EIT text used for
>> terrestrial schedule event names and descriptions. From March 2015, TVNZ
>> began compressing the EIT schedule again. Compressing the EIT text in
>> the schedule would not achieve the same receiver use given the
>> terrestrial EIT only has limited programme details. Receivers that don't
>> use the BBC huffman tables will either display no details or display
>> garbage characters."
>>
>> If TVNZ is really compressing the EIT using Huffman coding then the
>> MythTV EIT decoding code must be pretty clever to decompress it without
>> access to the Huffman lookup table(s). (Unless the Huffman table is
>> embedded in the EIT data in some standard way maybe?)
>>
>> After reading about how the BBC got OFCOM approval to implement "content
>> protection" for their HD service and some of the interweb comments about
>> how this could affect MythTV users I am nervous about TVNZ's plans. As
>> the paragraph above from Wikipedia says you can't decompress data that
>> has been compressed with Huffman coding unless you know the Huffman
>> decoding tree/lookup table. If TVNZ (and others?) follow the BBC path
>> and compress the EPG and require users to get a licenced copy of the
>> Huffman table then we'll lose our relatively simple access to the EPG
>> over the air.
>>
>> Also it could be the thin end of the wedge heading towards encryption of
>> "premium" content although I don't see why this would be allowed on
>> Freeview. But given what OFCOM allowed the BBC to do you never know what
>> warped reasoning might allow Freeview content to be encrypted.
>>
>> Hopefully my fears are completely ungrounded and we can continue on our
>> merry, open source way with our EPG and recording working fine.
>
> If they are using the same table as FreeSat this has already been
> implemented in MythTV
>
> https://code.mythtv.org/trac/ticket/6498#no1
>
> It would be interesting to see of epgsnoop could be updated to include the
> huffman tables.
>
> Looks like another EIT grabber already has the huffman support merged from
> MythTV.
> - https://github.com/ubaldus/tv_grab_dvb_plus
>

Having play against DTT with tv_grab_dvb_plus


$ ./src/tv_grab_dvb_plus -a 2 -d DEBUG -o /tmp/dtt.xml
tv_grab_dvb_plus DEBUG midnight today="20150626000000 +1200"
tv_grab_dvb_plus DEBUG start of period="20150626000000 +1200"
tv_grab_dvb_plus DEBUG end of period="20160625000000 +1200"
tv_grab_dvb_plus ERROR data or length is wrong for pid 20 (0x14) tableid
112 (0x70), len 8. skipping packet.
tv_grab_dvb_plus ERROR data or length is wrong for pid 20 (0x14) tableid
112 (0x70), len 8. skipping packet.
tv_grab_dvb_plus ERROR data or length is wrong for pid 20 (0x14) tableid
112 (0x70), len 8. skipping packet.
tv_grab_dvb_plus ERROR data or length is wrong for pid 20 (0x14) tableid
112 (0x70), len 8. skipping packet.
tv_grab_dvb_plus ERROR data or length is wrong for pid 20 (0x14) tableid
112 (0x70), len 8. skipping packet.
tv_grab_dvb_plus ERROR data or length is wrong for pid 20 (0x14) tableid
112 (0x70), len 8. skipping packet.
tv_grab_dvb_plus ERROR data or length is wrong for pid 20 (0x14) tableid
112 (0x70), len 8. skipping packet.
tv_grab_dvb_plus DEBUG timeout occurred
tv_grab_dvb_plus DEBUG freesat huffman average expansion ratio: 3.000000

Looks like the huffman decode works.

Wonder if this can be merged into epgsnoop?

--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email - steven@openmedia.co.nz
website - http://www.openmedia.co.nz

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