1seg

Lore & Background

1seg uses a single 428 kHz segment of an ISDB-T channel, with QPSK modulation, 2/3 forward error correction, and 1/4 guard ratio, providing a total datarate of 416 kbit/s. The television system employs H.264/MPEG-4 AVC video and HE-AAC audio multiplexed into an MPEG transport stream, with maximum video resolution of 320x240 pixels and video bitrate between 220 and 320 kbit/s. Audio bitrate ranges from 48 to 64 kbit/s, while additional data such as EPG and interactive services uses BML and occupies 10 to 100 kbit/s of bandwidth.

In Brazil, 1seg was established in late 2007 starting in a few cities, with a 30 fps transmission setting, differing from Japan's 15 fps setting. By 2014, approximately 62% of Brazil's population was covered by digital TV.

The first commercially available 1seg phone was the Sanyo W33SA, released in December 2005 or early 2006, though some sources cite the W32SA or other models as earlier contenders. The 1seg multi-program service (sometimes called 1seg2) began on April 1, 2008, with Tokyo MX being the first broadcaster to launch it.

Reader's Guide

1seg represents a significant innovation in mobile broadcasting, enabling television reception on portable devices such as mobile phones, car navigation systems, handheld game consoles, and electronic dictionaries. Its integration into ISDB-T allowed countries across Latin America and Asia to adopt a unified digital TV standard with mobile capabilities. The service's popularity in Japan was notable: by November 2007, approximately 63.5% of mobile phones sold in Japan could receive 1seg broadcasts, and by the end of fiscal year March 2008, 64.2% of phones had 1seg capability. Japanese regulation initially required 1seg programs to be the same as HDTV broadcasts, but this was revised on April 1, 2008, allowing experimental programs. Multiple-program arrangement (1seg2) began in June 2008, enabling simultaneous broadcast of two programs on a single segment. Conditional access and copy control are implemented via a Broadcast Flag-like structure, forcing devices to encrypt stored recordings and disallowing copies. In Brazil, the long-term outlook for 1seg is shifting as the country began commercial rollout of ATSC 3.0-based DTV+ in 2026, though ISDB-T and 1seg are expected to remain in parallel use for 10–15 years.

Did You Know?

• 1seg uses a single 428 kHz segment of an ISDB-T channel, leaving 12 segments for HDTV.
• The first mobile phone to support 1seg was the Sanyo W33SA, released by au by KDDI in autumn 2005.
• In Brazil, 1seg is broadcast at 30 fps, while Japanese broadcasts use 15 fps.
• Multiple-program arrangement (1seg2) began on June 23, 2008, with Tokyo MX being the first broadcaster.

Technical Architecture & Design Philosophy

1seg operates as a dedicated slice within the broader ISDB-T terrestrial broadcast framework. The system allocates each 6 MHz channel—spanning the UHF band from 470 to 770 MHz (806 MHz in Brazil)—into thirteen equal segments of 428 kHz bandwidth, separated by a 430 kHz guard band to prevent cross-channel interference. Twelve of these segments carry the full HDTV signal, while the thirteenth is reserved exclusively for mobile receivers, giving the service its name. The 1seg transport stream employs QPSK modulation with a 2/3 forward error correction code and a 1/4 guard interval, yielding a total datarate of 416 kbit/s. Video is encoded in H.264/MPEG-4 AVC at a maximum resolution of 320×240 pixels, with bitrates ranging from 220 to 320 kbit/s. Audio follows the HE-AAC profile at 48–64 kbit/s. The remaining 10 to 100 kbit/s is allocated to Broadcast Markup Language data, program guides, and interactive services. Conditional access is handled not through content encryption but via a Copy Control Descriptor that forces devices to encrypt stored recordings and blocks duplication.

Global Adoption & Regional Variations

What began as a Japanese mobile broadcasting experiment in 2005 and a commercial service on April 1, 2006, quickly transcended national borders. Brazil adopted the technology in late 2007, initially limited to a handful of cities, and introduced a notable modification: its 1seg streams run at 30 frames per second rather than Japan's 15 fps setting. By 2014, roughly 62 percent of Brazil's population fell within range of digital TV signals carrying 1seg, with the government setting a target of full national coverage by 2016. The standard, formalized regionally as ISDB-Tb, subsequently spread across South America—Argentina, Peru, Chile, Ecuador, Venezuela, Bolivia, and Paraguay all followed Brazil's lead in implementation. The Philippines joined the broader ISDB-T family through the closely related ISDB-T International variant. This wave of adoption made 1seg one of the most widely deployed mobile terrestrial broadcast technologies in the developing world, establishing a shared technical foundation for digital television across Latin America and parts of Southeast Asia.

Device Ecosystem & Market Penetration

The 1seg ecosystem extended far beyond mobile telephones, embedding itself into an astonishing variety of consumer electronics. In Japan, the first phone to carry the tuner was the Sanyo W33SA, released by carrier au in autumn 2005. By November 2007, JEITA data showed that 63.5 percent of the 4.806 million phones sold that month could receive 1seg, and the share climbed from 26.8 percent in April 2007 to 64.2 percent by March 2008. Beyond phones, the technology appeared in Sharp electronic dictionaries, Sony Walkman players, Kodak OLED displays, car navigation units from Sanyo and Pioneer, and even handheld gaming hardware—the PSP-2000 tuner and Nintendo DS's "DS Terebi" add-on both supported 1seg reception. PC-attachable USB receivers from Pixela, SKNET, and Cowon broadened access further. However, the rise of 5G NR and unlimited data plans has gradually diminished the service's relevance, and newer Japanese iOS and Android devices increasingly omit the tuner. In Brazil, the 2026 commercial rollout of ATSC 3.0-based DTV+ signals a similar long-term transition, though ISDB-T and 1seg are expected to persist in parallel for another ten to fifteen years.

Content Innovation & Interactive Services

1seg was never merely a low-resolution copy of the main broadcast; it evolved into a distinct content channel with its own interactive services. Broadcast Markup Language, or BML, allowed stations to push text-based data—news headlines, sports scores, weather forecasts, and critical emergency alerts such as Earthquake Early Warning—directly to viewers' screens at no cost, with hyperlinks directing users to the broadcaster's website for fuller stories. Program guide information, notably, travels in a separate EIT stream rather than within BML itself. A landmark regulatory shift on April 1, 2008, lifted the prior requirement that 1seg content mirror the HDTV feed, opening the door for experimental and third-party programming. The most ambitious technical innovation was multiple-program arrangement, or "1seg2," pioneered by Tokyo MX on June 23, 2008, which split the single segment to air two programs simultaneously. NHK Educational TV followed in April 2009 and Nara Television in December 2009. Most receivers manufactured after September 2008 were built to handle this dual-stream format, effectively doubling the service's programming capacity within the same 428 kHz slice.

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