The Radio Data System transmits supplementary information in binary format, for example the station name or travel information, on an inaudible audio subcarrier of a radio program. This interface is aimed at devices capable of receiving and decoding RDS information. For more information see the core RDS standard and the RBDS standard . Note that the RBDS standard as is used in the USA is almost identical to the RDS standard. Any RDS decoder can also handle RBDS. Only some of the fields have slightly different meanings. See the RBDS standard for more information. The RBDS standard also specifies support for MMBS (Modified Mobile Search). This is a proprietary format which seems to be discontinued. The RDS interface does not support this format. Should support for MMBS (or the so-called 'E blocks' in general) be needed, then please contact the linux-media mailing list: &v4l-ml;.

Devices supporting the RDS capturing API set the V4L2_CAP_RDS_CAPTURE flag in the capabilities field of &v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl. Any tuner that supports RDS will set the V4L2_TUNER_CAP_RDS flag in the capability field of &v4l2-tuner;. Whether an RDS signal is present can be detected by looking at the rxsubchans field of &v4l2-tuner;: the V4L2_TUNER_SUB_RDS will be set if RDS data was detected. Devices supporting the RDS output API set the V4L2_CAP_RDS_OUTPUT flag in the capabilities field of &v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl. Any modulator that supports RDS will set the V4L2_TUNER_CAP_RDS flag in the capability field of &v4l2-modulator;. In order to enable the RDS transmission one must set the V4L2_TUNER_SUB_RDS bit in the txsubchans field of &v4l2-modulator;.

RDS data can be read from the radio device with the &func-read; function. The data is packed in groups of three bytes, as follows: __u8 lsb Least Significant Byte of RDS Block __u8 msb Most Significant Byte of RDS Block __u8 block Block description Bits 0-2 Block (aka offset) of the received data. Bits 3-5 Deprecated. Currently identical to bits 0-2. Do not use these bits. Bit 6 Corrected bit. Indicates that an error was corrected for this data block. Bit 7 Error bit. Indicates that an uncorrectable error occurred during reception of this block. V4L2_RDS_BLOCK_MSK 7 Mask for bits 0-2 to get the block ID. V4L2_RDS_BLOCK_A 0 Block A. V4L2_RDS_BLOCK_B 1 Block B. V4L2_RDS_BLOCK_C 2 Block C. V4L2_RDS_BLOCK_D 3 Block D. V4L2_RDS_BLOCK_C_ALT 4 Block C'. V4L2_RDS_BLOCK_INVALID 7 An invalid block. V4L2_RDS_BLOCK_CORRECTED 0x40 A bit error was detected but corrected. V4L2_RDS_BLOCK_ERROR 0x80 An incorrectable error occurred.