[mythtv-users] 480i Anamorphic Channels
Stephen Worthington
stephen_agent at jsw.gen.nz
Wed Mar 4 11:29:43 UTC 2020
On Tue, 3 Mar 2020 14:12:04 -0800, you wrote:
>This question is not specifically related to MythTV, but I figure
>someone on this list would know the answer.
>
>A local ATSC station added a new sub channel. This channel is broadcast
>in an anamorphic 480i sub channel. The content is 16:9 aspect ratio,
>but is displayed on my TV and my MythTV squished horizontally with black
>bars on the side. Sure, I can change the aspect ratio to 16:9 during
>playback and it displays correctly, but there are other such 480i
>anamorphic channels with 16:9 aspect ratio content that I do not need to
>do this.
>
>Is there some kind of broadcast flag that the broadcaster is omitting
>that should indicate this to the playback device (TV, MythTV, etc.)?
>Before I bring it up with the broadcaster, I would at least like to
>think I know what I am talking about.
>
>Jay
That certainly sounds like a broadcaster error. The display aspect
ratio is as the broadcaster says it should be, so get them to fix it.
I am not sure exactly how it is done in ATSC streams, but in video
files there are usually two settings, one for the actual frame size
and one for the displayed frame size. Alternatively, there can be an
actual frame size setting and an aspect ratio setting.
As an example, here in New Zealand our satellite provider broadcasts a
number of DVB-S2 "HD" channels where the actual frame size is
1440x1080, but it is set to display as 1920x1080. Here is what
mediainfo has to say about a recording from such a channel:
General
ID : 14 (0xE)
Complete name : 10070_20200302093900.ts
Format : MPEG-TS
File size : 1.43 GiB
Duration : 29 min 59 s
Overall bit rate mode : Variable
Overall bit rate : 6 821 kb/s
Video
ID : 1001 (0x3E9)
Menu ID : 1 (0x1)
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High at L4
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, ReFrames : 4 frames
Format settings, GOP : M=4, N=24
Codec ID : 27
Duration : 29 min 58 s
Bit rate : 6 322 kb/s
Width : 1 440 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate : 25.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Interlaced
Scan type, store method : Separated fields
Scan order : Top Field First
Bits/(Pixel*Frame) : 0.163
Stream size : 1.32 GiB (93%)
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
Audio
ID : 1101 (0x44D)
Menu ID : 1 (0x1)
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 2
Format settings : Joint stereo
Codec ID : 3
Duration : 29 min 59 s
Bit rate mode : Constant
Bit rate : 160 kb/s
Channel(s) : 2 channels
Sampling rate : 48.0 kHz
Frame rate : 41.667 FPS (1152 SPF)
Compression mode : Lossy
Delay relative to video : -1 s 50 ms
Stream size : 34.3 MiB (2%)
Language : English
Text
ID : 1901 (0x76D)-801
Menu ID : 1 (0x1)
Format : Teletext Subtitle
Language : English
Note the "Width", "Height" and "Display aspect ratio" values.
And here is the output of mythffprobe on the same file:
ffprobe version 4.0.2 Copyright (c) 2007-2018 the FFmpeg developers
built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04.1)
configuration: --arch=x86 --sysinclude=/usr/include --cc='ccache
gcc' --cxx='ccache g++' --ld=gcc --cpu=generic --target_os=linux
--pkg_config=pkg-config --prefix=/usr --libdir=/usr/lib --as=gcc
--objcc=gcc --dep_cc=gcc --host_cc=gcc --host_ld=gcc
--disable-cross-compile --enable-libmp3lame --enable-libx264
--disable-libx265 --enable-libvpx --disable-libxvid --enable-vdpau
--enable-libxml2 --enable-libass --disable-dxva2 --enable-libbluray
--disable-libfontconfig --disable-libfreetype --disable-libiec61883
--enable-crystalhd --enable-sdl2 --enable-ffplay --enable-vaapi
--extra-cflags=' -w' --extra-ldflags= --enable-stripping --strip='echo
skipping strip' --disable-manpages --disable-podpages --disable-doc
--disable-nvenc --enable-shared --disable-static --enable-gpl
--enable-pic --disable-demuxer=mpegtsraw --disable-indev=dshow
libavutil 56. 14.100 / 56. 14.100
libavcodec 58. 18.100 / 58. 18.100
libavformat 58. 12.100 / 58. 12.100
libavdevice 58. 3.100 / 58. 3.100
libavfilter 7. 16.100 / 7. 16.100
libswscale 5. 1.100 / 5. 1.100
libswresample 3. 1.100 / 3. 1.100
libpostproc 55. 1.100 / 55. 1.100
[snipped out warning messages]
[mpegts @ 0x5600350c8800] PES packet size mismatch
Input #0, mpegts, from '10070_20200302093900.ts':
Duration: 00:29:59.83, start: 21566.971311, bitrate: 6818 kb/s
Stream #0:0[0x3e9]: Video: h264 (High), yuv420p(tv, bt709, top
first), 1440x1080 [SAR 4:3 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
Stream #0:1[0x44d](eng): Audio: mp2, 48000 Hz, stereo, fltp, 160
kb/s
Stream #0:2[0x76d](eng): Subtitle: dvb_teletext
Unsupported codec with id 94215 for input stream 2
It reports that "Stream #0:0" is 1440x1080 with SAR (storage aspect
ratio) of 4:3 but a DAR (display aspect ratio) of 16:9.
Here is the Wikipedia page that explains it:
https://en.wikipedia.org/wiki/Pixel_aspect_ratio
So I think what you want to ask your broadcasters for is for them to
set the DAR to 16:9.
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