[mythtv-users] Getting 1080p from comcast cable boxes (Was VUDU)

Wed Feb 25 02:42:27 UTC 2009

On Tue, Feb 24, 2009 at 05:47:01PM -0800, Robert McNamara wrote:
> On Tue, Feb 24, 2009 at 5:28 PM, Brad Templeton
> > The AMC-HD recordings I get out of firewire are definitely progressive
> > (or at least identified as such by mythtv) and at 30 fps.
> 
> can you dd out a short sample and upload it somewhere?

I can, but you might be able to glean a bunch from this output from
mplayer.   Some of it comes from later in the TS -- brief switches to
short stretches of 24fps progressive.  
> 
> >
> Like I said 60 fields, 30 frames.  Telecining (and inverse telecine)
> have nothing to do with 1080i and p, they have to do with framerates.
> If they *were* doing an inverse telecine locally, you would be getting
> a 24 frame signal, not a 30 frame signal (although I understand that's
> not the point of your query).

I understand the difference between fields and frames, but a 30 fps
progressive stream does not have two fields per frame, while an
interlaced one would.   As I am sure you know, some tools report
60 fields per second as 60 frames per second, but that is not the
case here.

> 
> No nationally syndicated channel is broadcasting 1080p.  They are all
> SD, 720p, or 1080i.  Channels which broadcast in 720p are generally at
> 60 frames per second to take advantage of smoother motion (sports
> channels, most commonly).  Channels at 1080i do so because they tend
> to have less motion and want to take advantage or greater resolution
> (Dramas).  Of the national networks, CBS and NBC are at 1080i.  Fox
> and ABC are 720p.

In the broadcast arena it's all 480i, 720p and 1080i, of course, as that is
all some TVs are set to handle.  I wish that stations would do their SDTV
in 480p but nobody seems to.

However, there is no such constraint on self-contained systems where
the channel is never OTA, and is transmitted by private links to
cable and satellite providers.   They _could_ transmit a 24fps progressive
1080 line signal to the cable company, and the cable company could then
have its STB convert that to what the TV wants.  What I don't know is
if they actually do this.  It makes a great deal of sense to do, but
who said they have to do what makes sense.

> This is the reason it was such a "big deal" when Dish said they were
> going to start providing 1080p movies.  They were amongst the first
> "broadcasters" to announce such a move.

Well, to some 1080p means 1080p 60 full-frames/second which is quite rare,
very little is even shot at that rate.
> 
> I'm not saying it's not possible that your local headend is doing some
> jiggery-pokery to deinterlace a 1080i signal, but I *am* saying from
> firsthand experience that the AMC-HD feed is 1080i.

By firsthand experience, you mean you have accessed the private feed
coming out of AMC HQ going to Comcast, DirectTV and Dish network?
> 
> > You suggest AMC-HD sends out 1080i to Comcast, and they inverse telecine
> > it and send it out over QAM as 1080p, and then have their cable boxes
> > convert it to 1080i and 720p to drive HDTVs?    Could be true but makes
> > a lot less sense than the other.
> 
> Again, inverse telecine is the process of taking a film-sourced 30 or
> 60 frame signal and "de-converting" it to a 24 frame signal.  Has
> nothing to do with resolution or interlacing.

When you are converting a 1080i telecine back to a 24 fps _progressive_
signal, then it most certainly does involve interlacing, because you
are deinterlacing.    Since almost all telecining done for broadcast
involves interlacing done to film frames, almost all reverse telecine
involves deinterlacing (a particular custom tuned deinterlace which
knows what sort of pulldown and interlace was done to telecine)

> Uni HD is another 1080i channel.  Again, from direct experience with
> the feed I can guarantee that it's interlaced.  Once again, I'm not
> trying to be anti-social and say that it's not *possible* that there's
> something being done locally, just that a) it would be useless (and
> almost deceptive) as the source is interlaced and b) if true, it's
> certainly the exception and not the rule.

Well, if the feed out is interlaced, then what is happening is that
Comcast is deinterlacing in their head end or in the cable box.

The cable box had deinterlace hardware, as you are allowed to hook up
a progressive TV to it over HDMI if I recall correctly from the
setup process.
> 
> I'm not trying to be snarky in asking for samples, I genuinely would
> like to see what if any changes have been made to the stream, and if
> there is a misconception, explain how it might have happened.

I'll get some samples for you if this doesn't tell you enough.  
> 

MPlayer 1.0rc2-4.2.3 (C) 2000-2007 MPlayer Team
CPU: Intel(R) Core(TM)2 CPU          6600  @ 2.40GHz (Family: 6, Model: 15, Stepping: 6)
CPUflags:  MMX: 1 MMX2: 1 3DNow: 0 3DNow2: 0 SSE: 1 SSE2: 1
Compiled with runtime CPU detection.
mplayer: could not connect to socket
mplayer: No such file or directory
Failed to open LIRC support. You will not be able to use your remote control.

Playing 7769_20090207200000.mpg.
TS file format detected.
VIDEO MPEG2(pid=2048) AUDIO A52(pid=2050) NO SUBS (yet)!  PROGRAM N. 1
VIDEO:  MPEG2  1920x1080  (aspect 3)  29.970 fps  38810.4 kbps (4851.3 kbyte/s)
xscreensaver_disable: Could not find XScreenSaver window.
==========================================================================
Opening video decoder: [mpegpes] MPEG 1/2 Video passthrough
VDec: vo config request - 1920 x 1080 (preferred colorspace: Mpeg PES)
Could not find matching colorspace - retrying with -vf scale...
Opening video filter: [scale]
The selected video_out device is incompatible with this codec.
Try appending the scale filter to your filter list,
e.g. -vf spp,scale instead of -vf spp.
VDecoder init failed :(
Opening video decoder: [libmpeg2] MPEG 1/2 Video decoder libmpeg2-v0.4.0b
Selected video codec: [mpeg12] vfm: libmpeg2 (MPEG-1 or 2 (libmpeg2))
==========================================================================
==========================================================================
Forced audio codec: mad
Opening audio decoder: [liba52] AC3 decoding with liba52
Using SSE optimized IMDCT transform
Using MMX optimized resampler
AUDIO: 48000 Hz, 2 ch, s16le, 384.0 kbit/25.00% (ratio: 48000->192000)
Selected audio codec: [a52] afm: liba52 (AC3-liba52)
==========================================================================
AO: [pulse] Failed to connect to server: Connection refused
AO: [alsa] 48000Hz 2ch s16le (2 bytes per sample)
Starting playback...
VDec: vo config request - 1920 x 1080 (preferred colorspace: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1.78:1 - prescaling to correct movie aspect.
VO: [xv] 1920x1080 => 1920x1080 Planar YV12
A:14128.6 V:14128.6 A-V: -0.006 ct: -1.315 712/708 17%  4%  0.7% 0 0
demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.
A:14129.0 V:14129.0 A-V:  0.040 ct: -1.293 722/718 17%  4%  0.7% 0 0
demux_mpg: 30000/1001fps NTSC content detected, switching framerate.
Warning! FPS changed 23.976 -> 29.970  (-5.994005) [4]  4%  0.7% 0 0
A:14129.7 V:14129.7 A-V:  0.006 ct: -1.246 743/736 17%  4%  0.7% 0 0
demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.
A:14133.3 V:14133.2 A-V:  0.041 ct: -1.190 830/823 16%  4%  0.7% 0 0
demux_mpg: 30000/1001fps NTSC content detected, switching framerate.
Warning! FPS changed 23.976 -> 29.970  (-5.994005) [4]  4%  0.7% 0 0
A:14156.0 V:14156.1 A-V: -0.003 ct: -1.133 1514/1501 15%  4%  0.7% 0 0
demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.
A:14156.5 V:14156.4 A-V:  0.039 ct: -1.108 1525/1511 15%  4%  0.7% 0 0
demux_mpg: 30000/1001fps NTSC content detected, switching framerate.
Warning! FPS changed 23.976 -> 29.970  (-5.994005) [4]    4%  0.7% 0 0
A:14164.3 V:14164.3 A-V: -0.006 ct: -1.050 1762/1743 16%  4%  0.7% 0 0
demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.
A:14164.8 V:14164.8 A-V:  0.039 ct: -1.028 1775/1755 16%  4%  0.7% 0 0
demux_mpg: 30000/1001fps NTSC content detected, switching framerate.
Warning! FPS changed 23.976 -> 29.970  (-5.994005) [4]    4%  0.7% 0 0
A:14165.0 V:14165.0 A-V:  0.040 ct: -1.013 1780/1759 16%  4%  0.7% 0 0
demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.
A:14166.5 V:14166.4 A-V:  0.043 ct: -0.885 1818/1797 16%  4%  0.7% 0 0
demux_mpg: 30000/1001fps NTSC content detected, switching framerate.
Warning! FPS changed 23.976 -> 29.970  (-5.994005) [4]    4%  0.7% 0 0
A:14166.8 V:14166.8 A-V:  0.027 ct: -0.855 1829/1806 16%  4%  0.7% 0 0
demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate.
A:14167.4 V:14167.4 A-V:  0.049 ct: -0.806 1845/1821 16%  4%  0.7% 0 0
demux_mpg: 30000/1001fps NTSC content detected, switching framerate.
Warning! FPS changed 23.976 -> 29.970  (-5.994005) [4]    4%  0.7% 0 0
A:14169.5 V:14169.5 A-V: -0.000 ct: -0.743 1908/1881 16%  4%  0.7% 0 0