Download Report

Digital TV on Linux
Mauro Carvalho Chehab
Linux Kernel Expert
Samsung Open Source Group
Oct 14, 2014
Open Source Group – Silicon Valley
Samsung Research Brazil
Not to be used for commercial purpose without getting permission
All information herein are my own and may not represent the company's positions, strategies or opinions
© 2014 SAMSUNG Electronics Co.
Digital TV challenges
●
Major standards:
–
–
–
–
ATSC - Advanced Television System Committee
● Defined in United States
DVB - Digital Video Broadcasting
● Defined in Europe
ISDB – Integrated Services Digital Broadcasting
Terrestrial
● Defined in Japan
DTMB - Digital Terrestrial Multimedia Broadcast
● Defined in China
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© 2014 SAMSUNG Electronics Co.
Digital TV challenges
●
Digital TV variants:
–
–
–
Terrestrial (air) standards are used by air
broadcasts: ATSC, DVB-T, DVB-T2, ISDB-T,
DMB;
Cable standards are used by cable operators:
DVB-C, DVB-C2, ClearQAM (DVB-C Annex B),
ISDB-C;
Satellite standards are used by Satellite
operators: DVB-S, DVB-S2, ISDB-S.
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Digital TV Terrestrial Standards
Source: http://en.wikipedia.org/wiki/File:Digital_broadcast_standards.svg
Note: DVB-T2 is gradually replacing DVB-T
Open Source Group – Silicon Valley
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Updated in May, 2014
© 2014 SAMSUNG Electronics Co.
TV Digital standards
Audio Elem. Stream
Video Elem. Stream
MPEG2-BC
280i LD
Channel
480iSDTV
DOLBY
AC3
MPEG4AAC
720pEDTV
1080iHDTV
MPEG4
MPEG2
MPEG2 – Transport Stream
Transport
Modulation
MPEG2AAC
VSB QAM QPSK COFDM COFDM-BST TDS-OFDM
1.7 Mhz
5 Mhz
6 Mhz
7 Mhz
8 Mhz
10 Mhz
Copyright © 2006-2014 Mauro Carvalho Chehab – GPLv2 licensed
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Samsung Research Brazil
© 2014 SAMSUNG Electronics Co.
TV Digital Linux Mapping
Userspace
Audio Elem. Stream
Video Elem. Stream
MPEG2-BC
280i LD
Channel
480iSDTV
DOLBY
AC3
MPEG4AAC
720pEDTV
1080iHDTV
MPEG4
MPEG2
MPEG2 – Transport Stream
Transport
Modulation
MPEG2AAC
VSB QAM QPSK COFDM COFDM-BST TDS-OFDM
1.7 Mhz
5 Mhz
6 Mhz
7 Mhz
8 Mhz
10 Mhz
Kernelspace
Copyright © 2006-2014 Mauro Carvalho Chehab – GPLv2 licensed
Open Source Group – Silicon Valley
Samsung Research Brazil
© 2014 SAMSUNG Electronics Co.
Media device block diagram
Tuner
FM/TV
Frontend
SEC
Audio decoder
Conditional Access Module
Audio encoder
Digital TV
Button Key/IR input logic
System Bus
Radio / Analog TV
I2C Bus
Video decoder
Video encoder
Smartcard
Transport Stream filter
EEPROM
Sensor
Webcam
Processing blocks
PCI,
USB,
PCIe,
...
Bridge to CPU/Chipset bus
PS.: picture is not complete: other blocks may be present,
Like audio/video A/D and D/A, HDMI decoder/encoder, etc.
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© 2014 SAMSUNG Electronics Co.
●
Video4Linux API (version 2)
Tuner
FM/TV
Audio decoder
Audio encoder
Video decoder
Video encoder
For webcams, video inputs/outputs
and radio, video and analog TV
● Extensions for Software Digital
Radio were added recently
●
Radio / Analog TV
●
Sensor
Audio output uses the standard
ALSA API
Webcam
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© 2014 SAMSUNG Electronics Co.
●
Remote Controller / Input APIs
Button Key/IR input logic
Used for Remote Controllers and Webcam buttons
● It is an extension of the standard Linux Input API (evdev)
●
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© 2014 SAMSUNG Electronics Co.
Linux Kernel DTV APIs
DVB Frontend API
Frontend
SEC
DVB CA API
DVB Demux API
Conditional Access Module
Transport Stream filter
Smartcard
Digital TV
●
Despite being called Linux DVB API, it covers all standards
●
Each frontend, CA and Demux device on a DTV card is exported
●
●
The frontend control is complex, as it is standard-dependent and
Country dependent;
Satellite Equipment Control (SEC) setup is also complex:
–
Controls LNBf and smart devices (DiSEqC);
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© 2014 SAMSUNG Electronics Co.
Media Controller API
●
●
●
To control complex devices with configurable pipelines
Currently, used only on embedded devices and on UVC (USB
Video Class)
Subdev API: controls each logical element on complex devices
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Media controller API
●
●
Discovering a device internal topology
–
hardware devices are modeled as an oriented graph
–
building blocks called entities connected through pads.
An entity is a media hardware or software building block
–
●
●
correspond to logical blocks: physical/logical hardware
devices, DMA channels, physical connectors
A pad is a connection endpoint
–
Represents interactions between entities
–
Data flows from the entity's output to one or more entity inputs
A link is a point-to-point oriented connection between two
pads
–
Data flows from source to sink pads
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© 2014 SAMSUNG Electronics Co.
Sub-devices
●
sub-devices are usually kernel-only objects
–
If a driver implements the media device API:
Applications will be able to:
– enumerate the sub-devices
– discover the hardware topology
In addition to make sub-devices discoverable:
●
●
–
●
drivers can also choose to make sub-devices directly
configurable
sub-devices will feature a character device node
–
on which ioctls can be called to affecting directly that
subdevice
–
image formats can be negotiated on individual pads
●
Currently, only available for V4L2
●
Adding support for DVB will require more work
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© 2014 SAMSUNG Electronics Co.
Summary of Media Kernel APIs
●
APIs described at: http://linuxtv.org/downloads/v4l-dvb-apis/
–
Video4Linux API (version 2)
–
For webcams, video inputs/outputs and radio, video and
analog TV
Linux DVB API (version 5)
–
For digital TV inputs
Remote Controller / Input evdev APIs
–
For Remote Controllers
Media Controller and Subdev APIs
●
●
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To control complex devices with configurable pipelines
The Advanced Linux Sound Architecture (ALSA)
●
●
–
●
For audio inputs, outputs, mixers (and sequencers)
Standard input evdev API
–
For webcam/grabber buttons and remote controllers
14
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DVB API history
●
DVBv1: the old Nokia API (1998-1999?)
–
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DVBv2: major re-factoring step (2000-2002?)
–
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First version on Kernel – Jun/2003 – for Kernel v2.5.74
DVBv4: An abandoned WIP project (2004-2005)
–
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Stabilized the API for DVB-T/C/S; ATSC
DVBv3: namespace cleanups
–
●
Developed/Implemented for a Nokia project developed by
Convergence
Meant to add all features for STB, but never finished.
DVBv5: Current version
–
Committed in Kernel 2.6.28 (2008).
–
Added full multi-standard support. Frontend-only changes.
–
New standards generally support DVBv3 legacy calls, with
drawbacks
15
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MPEG-TS container example
Virtual Channel 17.1: playing movie (HD)
Program 1
(service ID 1000)
PHYSICAL
CHANNEL /
TRANSPONDER
MPEG
Transport
Stream
container
PID 100
Audio 1
PID 101
Audio 2
PID 102
Virtual Channel 17.2: playing news (SD)
Program 2
(service ID 2000)
Other PIDs
16
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Video
Video
PID 200
Audio 1
PID 231
Data
PID 554
NOTE:
The PID and Service ID
data are described on some
tables inside the MPEG-TS:
PAT/PMT plus:
SDT(DVB, ISDB) or
TVCT/CVCT (ATSC)
© 2014 SAMSUNG Electronics Co.
Kernel system calls used on media
●
The media API devices are accessed via Kernel system
calls:
–
open() - opens a device node for read or read/write
access;
–
close() - closes a device node, releasing resources;
–
ioctl() - sends/receives special commands to the device;
–
read() - reads some data from an input device;
–
write() - sends some data to an output device;
–
poll() - checks if something is a available for input, if
output finished or if an I/O error (or event) occurred;
–
mmap() - creates a shared memory to be used by both
the application and the device (currently, only V4L2).
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DVBv3 API
struct dvb_qpsk_parameters {
__u32
fe_code_rate_t
/* DVB-S */
symbol_rate;
fec_inner;
};
struct dvb_qam_parameters {
__u32
fe_code_rate_t
fe_modulation_t
/* DVB-C */
symbol_rate;
fec_inner;
modulation;
};
struct dvb_vsb_parameters {
fe_modulation_t
/* ATSC */
modulation;
};
struct dvb_ofdm_parameters {
fe_bandwidth_t
fe_code_rate_t
fe_code_rate_t
fe_modulation_t
fe_transmit_mode_t
fe_guard_interval_t
fe_hierarchy_t
/* DVB-T */
bandwidth;
code_rate_HP;
code_rate_LP;
constellation;
transmission_mode;
guard_interval;
hierarchy_information;
};
struct dvb_frontend_parameters {
__u32 frequency;
fe_spectral_inversion_t inversion;
union {
struct
struct
struct
struct
dvb_qpsk_parameters
dvb_qam_parameters
dvb_ofdm_parameters
dvb_vsb_parameters
qpsk;
qam;
ofdm;
vsb;
} u;
};
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Samsung Research Brazil
© 2014 SAMSUNG Electronics Co.
Digital TV frontend properties
●
●
The Linux DVB frontend API sets/gets the frontend properties.
At Linux DVB API version 5, it is based mainly on two ioctl()
syscalls:
–
FE_GET_PROPERTY: This ioctl call returns one or more
frontend properties.
Only requires read-only access to the device to read the
props from a cache.
FE_SET_PROPERTY: This ioctl call sets one or more frontend
properties.
●
–
–
Read/write access is required to write the props at the
kernel cache.
Each property consists of a key and its associated value.
–
Several properties can be get/set at the same time.
●
●
NOTE: other ioctls also defined at DVBv3 are still used, like:
–
FE_READ_STATUS – reads frontend lock status
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© 2014 SAMSUNG Electronics Co.
DVBv5 properties example
●
For example, to receive a DVB/C channel at 651 kHz, the
following properties should be filled with:
–
FREQUENCY = 651000000
–
MODULATION = QAM_256
–
INVERSION = INVERSION_AUTO
–
SYMBOL_RATE = 5217000
–
INNER_FEC = FEC_3_4
–
(inner convolutional code FEC = 3/4)
DVB_TUNE = <any value>
●
This special property writes data from the previous
properties stored at the cache into the hardware
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© 2014 SAMSUNG Electronics Co.
Digital TV demux settings
●
●
The DVB demux API provides ways to filter the MPEG TS and read
its contents
The most used ioctl syscals are the ones that set the filters:
–
DMX_SET_BUFFER_SIZE – Sets the size of the circular buffer
used to store the filtered data
–
DMX_SET_FILTER - This ioctl call sets up a MPEG-TS packet
filter according to the filter and mask parameters provided (up to
the 16 bytes of the packet can be filtered).
–
DMX_SET_PES_FILTER - This ioctl call sets up a Program
Elementary Stream (PES) filter according to the parameters
provided. It filters just the packet identifier (PID)
A PID equal to 0x2000 means to just send the entire MPEG-TS
as-is to userspace. Generally, only used for testing purposes,
especially on embedded or USB-based devices, as this eats a
lot of CPU time and bus bandwidth.
Once a filter is set, the data is read via the dvr device node, using
poll() and read() syscalls.
●
●
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© 2014 SAMSUNG Electronics Co.
Userspace library: libdvbv5
●
Written from scratch to fully support DVBv5;
●
Provide a standard way to work with all DVB standards;
●
●
Offers functions to discover the TV programs (“channels”) that are
inside a transport stream;
Offers functions to read/write files on both legacyformats used by
DVBv3 applications and to read/write data compatible with
DVBv5.
●
Used by DVBv5 utils, tvdaemon, Kaffeine (at linuxtv.org);
●
The API stabilized in April, 2014.
–
Released at v4l-utils version 1.4.0 (Sept, 8 2014)
–
Fully documented at v4l-utils version 1.6.0 (Oct, 5 2014)
–
Already packaged for Fedora and Debian (a Tizen package is
also available at linuxtv.org – pending to be pushed upstream)
–
New projects should start using it.
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© 2014 SAMSUNG Electronics Co.
The libdvbv5 library
●
●
●
The Library uses internally (key, value) sets, just like the DVBv5 API
–
All DVBv5 sets are supported
–
Additional properties for Satellite Equipment Control(SEC)
config
–
Additional properties for derived statistics;
The logic to configure SEC should be in userspace, as only the
application knows:
–
Satellite LNBf, with converts from C-Band/Ku-Band/... into SBand, used by the satellite TV devices;
–
Parameters to select the satellite dish/LNBf, to change the dish
position and to select the LNBf frequency range/polarization.
As the DVB evolved, there are different ways to do the same thing,
e. g. via the latest DVBv5 API spec or to use some fallback code
when running a DVBv5 API lower than version 5.10 or even DVBv3.
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The libdvbv5 features summary
●
●
●
●
●
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It abstracts the DVB version, supporting all types of drivers
from version 3.2 and up;
It allows setting parameters related to the satellite system;
It provides a way to receive the DVBv5 enhanced statistics
if available;
It provides decoders for several MPEG-TS descriptors
needed to identify the Packet IDs inside a MPEG-TS
program;
Provides functions to read files containing
channel/program properties;
Provides extra statistics like signal quality, BER and PER
measurements, etc.
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© 2014 SAMSUNG Electronics Co.
Example: tuning into a channel
dvb = dvb_fe_open(0, 0, 0, 0);
/* Opens adapter 0, frontend 0 */
dvb_file = dvb_read_file_format(“channel”, SYS_UNDEFINED, FILE_DVBV5);
entry = dvb_file->first_entry;
/* Use the first channel */
for (i = 0; i < entry->n_props; i++)
dvb_fe_store_parm(dvb, entry->props[i].cmd, entry->props[i].u.data);
dvb_file_free(dvb_file);
dvb_fe_set_parms(dvb);
while (1) {
char buf[256], p = buf;
int len = sizeof(buf), show = 1;
dvb_fe_get_stats(dvb);
dvb_fe_snprintf_stat(dvb, DTV_STATUS, NULL, 0, &p, &len, &show);
dvb_fe_snprintf_stat(dvb, DTV_QUALITY, "Qual", 0, &p, &len, &show);
fprintf(fd, "\t%s\n", buf);
}
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DVBv5 utils
●
DVBv5 utils:
–
Uses libdvbv5 as basis for scan/zap and read/write channel
files;
–
It consists of 4 tools:
dvbv5-scan
Scans the channel transponders and gets the services available
there
dvbv5-zap
Locks into a channel (zap), allowing other applications to get the
stream at the dvr devices or to monitor the stream
dvb-fe-tool
Lists frontend properties, allows to manually set the DVB frontend
delivery system and to monitor the frontend statistics
dvb-format-convert Converts from/to several other formats used by DVBv3 apps
●
Both DVBv5 utils and libdvbv5 are packaged together with
v4l-utils:
–
http://git.linuxtv.org/cgit.cgi/v4l-utils.git/
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GUI apps using libdvbv5
●
●
Kaffeine has a recent experimental addition of libdvbv5 support:
–
It is a KDE media player with support for several types of
input, including Digital TV (ATSC, DVB-S, DVB-S2 and DVBC);
–
The experimental patches also adds support for ISDB-T;
–
Should not be hard to add support for DVB-T2 and other
modern standards;
–
Need more testing and bug fixes;
–
Located at: http://git.linuxtv.org/cgit.cgi/mchehab/kaffeine.git/
Tvdaemon:
–
It is a TV streaming server;
–
It is a fork/rewrite of tvheadend;
–
Located at: https://github.com/neolynx/tvdaemon
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DVB-C Scan Example
$ dvbv5-scan ~/dvbc-teste -I channel
Scanning frequency #1 573000000
Lock
(0x1f) Quality= Good Signal= 100.00% C/N= -13.80dB
UCB= 0 postBER= 3.14x10^-3 PER= 0
Service SBT, provider (null): digital television
Service Globo, provider Globo: digital television
Service Record, provider (null): digital television
Service Band, provider (null): digital television
...
Service Trilhas Sonoras, provider (null): digital radio
New transponder/channel found: #2: 579000000
...
New transponder/channel found: #39: 507000000
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Service zap example
$ dvbv5-zap -c dvb_channel.conf "trilhas sonoras" -r
using demux '/dev/dvb/adapter0/demux0'
reading channels from file 'dvb_channel.conf'
service has pid type 05:
204
tuning to 573000000 Hz
audio pid 104
dvb_set_pesfilter 104
Lock
(0x1f) Quality= Good Signal= 100.00% C/N= -13.80dB
UCB= 70 postBER= 3.14x10^-3 PER= 0
DVR interface '/dev/dvb/adapter0/dvr0' can now be opened
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DVB DVR device play
$ mplayer -cache 800 /dev/dvb/adapter0/dvr0
MPlayer SVN-r37077-4.8.2 (C) 2000-2014 MPlayer Team
TS file format detected.
NO VIDEO! AUDIO MPA(pid=104) NO SUBS (yet)!
PROGRAM N. 0
==================================================================
Opening audio decoder: [mpg123] MPEG 1.0/2.0/2.5 layers I, II, III
AUDIO: 48000 Hz, 2 ch, s16le, 192.0 kbit/12.50% (ratio: 24000>192000)
Selected audio codec: [mpg123] afm: mpg123 (MPEG 1.0/2.0/2.5
layers I, II, III)
==================================================================
AO: [alsa] 48000Hz 2ch s16le (2 bytes per sample)
Video: no video
Starting playback...
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DVB transponder traffic monitor
$ dvbv5-zap -c dvb_channel.conf 573000000 -m
...
Lock
(0x1f) Quality= Good Signal= 100.00% C/N= -13.90dB
UCB= 384 postBER= 96.8x10^-6 PER= 0
dvb_set_pesfilter to 0x2000
PID
FREQ
SPEED
TOTAL
0000
9.88 p/s
14.5 Kbps
1 KB
0001
1.98 p/s
2.9 Kbps
376 B
0010
18.77 p/s
27.6 Kbps
3 KB
0011
48.42 p/s
71.1 Kbps
8 KB
0012
1455.53 p/s
2137.8 Kbps
270 KB
1fff
1033.60 p/s
1518.1 Kbps
192 KB
TOT
25296.44 p/s
37154.2 Kbps
4700 KB
...
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How to contribute
●
Main discussions and patches for TV on Linux:
–
●
●
Userspace/kernelspace: linux-media@vger.kernel.org
Upstream trees:
–
To test Kernel drivers: http://git.linuxtv.org/media_build.git
–
To develop Kernel drivers http://git.linuxtv.org/media_tree.git
–
v4l-utils, dvbv5 utils and libdvbv5: http://git.linuxtv.org/v4l-utils.git
Documentation:
–
Media APIs http://linuxtv.org/downloads/v4l-dvb-apis
–
libdvbv5 docs: http://linuxtv.org/docs/libdvbv5/index.html
●
Wiki pages: http://linuxtv.org/wiki/
●
IRC channel: irc.freenode.net
–
channels #v4l and #linuxtv
–
Can be assessed via http://webchat.freenode.net/
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Questions?
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