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The hidden rules of SMPTE 291M: Why are these encoding formats so important?
In the fields of television broadcasting and digital media, with the advancement of technology, people have higher and higher requirements for data transmission. Against this background, the SMPTE 291M standard emerged to respond to this demand, providing rigorous specifications for the embedding of non-video data. This data is called "auxiliary data" (Ancillary data), which can be audio, other basic content or metadata, and plays a vital role in improving the viewing experience and transmission efficiency. This article will deeply explore the SMPTE 291M standard and its application in digital transmission, and remind readers to think: How will data transmission technology further evolve in the future?
Definition and application of auxiliary data
Auxiliary data is data that is appended to the primary data and transmitted using the same transfer form. Common examples include cover art images for media files or streams, or digital data added to radio or television broadcasts. In the context of television systems, ancillary data (referred to as ANC data) refers to a way of embedding non-video information through a serial digital interface. It standardizes the format of several such packets through the SMPTE standard.
Standards and technical details
Ancillary data is standardized by the SMPTE 291M standard, which specifies the placement of ancillary data packets and their spatial format. According to the standard, auxiliary data can be located in the non-video portion of the horizontal scan line, called horizontal auxiliary data (HANC). In addition, ancillary data can also be located in non-video areas of the video frame, called vertical ancillary data (VANC).
There are two common types of auxiliary data packets: HANC and VANC.
Data packet format
All ANC data packets must start with a startup sequence. For currently widely used component interfaces, the startup sequence is 0x000 0x3FF 0x3FF. After this startup sequence, the format of the data packet will include fields such as Data Identifier (DID), Secondary Data Identifier (SDID) or Data Block Number (DBN), and Data Count (DC).
Note: The value of DID ranges from 1 to 255, and 0 is a reserved value.
Application example: Embedding auxiliary information
Embedding auxiliary audio usually refers to the audio track of a film program. The standards SMPTE 272M (standard definition) and SMPTE 299M (high definition and 3G) define how to embed audio in the auxiliary space. These standards provide up to 16 channels of PCM audio, while 3G allows up to 32 channels. Unlike other data packets, embedded audio data packets are type 1 data packets that usually contain message-related metadata.
Error detection: EDH
In the standard definition interface, EDH packets are used for error detection, but this is no longer needed in the high definition interface because the HD-SDI interface has a built-in cyclic redundancy check (CRC). The development of these technologies not only effectively improves signal stability, but also improves quality and reliability during television production and broadcast.
Conclusion
As digital media technology continues to advance, the auxiliary data specified by the SMPTE 291M standard will become increasingly important in future applications. This standard not only ensures effective synchronization of audio and video, but also facilitates the seamless transmission of additional information. Taking into account potential future technological developments, could such a standard be combined with more efficient data transmission technologies to enhance the overall viewing experience?
