Retrieving ID3 Tags

Retrieving ID3 Tags

The video player must have the ability to extract ID3 tags and supply them to the Browser SDK, based on the HLS standard.

• An ID3 tag spans two PES packets.
  • In the first PES packet, look for www.nielsen.com, this is the start of the ID3 tag. Continue to parse the first PES packet until the undefined char "\ufffd" is found. This forms the first half of the ID3 tag
  • In the second PES packet, identify the end pattern – a regEx of /(\/\d+){3}/ and look to remove the lowest index of either "\x00" and/or "\ufffd". Now the second packet has been appended and the demarcation of the Nielsen-specific data has been defined.

Follow the procedure below, to extract Nielsen ID3 tags from an MPEG-2 transport stream (including HLS streams).

1. Parse the Program Map Table (PMT) to find the PID of the metadata stream. Confirm the presence of the metadata descriptor described in section 2.3.3 of Apple’s “HTTP Live Streaming Metadata Spec.pdf”. Only private streams with metadata descriptor present should be considered as ID3-tag metadata streams.
2. Parse the HLS/Transport stream for any PES header with the PID found in step 1.
3. Follow standard MPEG-2 parsing procedures to locate the start of the payload of the PES packet.
4. Copy the PES payload into a buffer.
5. The ID3 tag spans 2 PES packets. Parse the stream for the next packet whose PID is set to the PID found in step 1. Typically the ID3 Tag is of 249 bytes. The steps below guide towards extraction of the ID3 tag
   1. In the first PES packet, look for "www.nielsen.com" , this is the start of the ID3 tag. Keep on parsing the first PES packet until the undefined char "\ufffd" is found. This forms the first half of the ID3 tag
   2. In the second PES packet, identify the end pattern, a regEx of /(\/\d+){3}/ and look to remove the lowest index of either “\x00” and/or “\ufffd”. Now the second packet has been appended and the demarcation of the Nielsen specific data has been defined. This segment can be simply substringed.
   3. Concatenate this substringed segment with the payload derived from the first packet get the ID3 payload.
6. Check the length of the contents in the buffer to make sure that it is equal to the size of a Nielsen ID3 tag.
7. Ensure that the ID3 byte array is converted into the string and escape it, so that the SDK can consume it.

Repeat steps 2 through 7 for all ID3 tags in the stream.

References

• ISO/IEC 13818-1:2007 Information technology – Generic coding of moving pictures and associated audio information: Systems
• https://developer.apple.com/library/content/documentation/AudioVideo/Conceptual/HTTP_Live_Streaming_Metadata_Spec/

Sample ID3 tags

• www.nielsen.com/X100zdCIGeIlgZnkYj6UvQ==/X100zdCIGeIlgZnkYj6UvQ==/AAAB2Jz2_k74GXSzx4npHuI_JwJd3QSUpW30rDkGTcbHEzIMWleCzM-uvNOP9fzJcQMWQLJqzXMCAxParOb5sGijSV9dNM3QiBniJYGZ5GI-lL1fXTTN0IgZ4iWBmeRiPpS9AAAAAAAAAAAAAAAAAAAAAFJWFM5SVhTONNU=/00000/00000/00
• www.nielsen.com/X100zdCIGeIlgZnkYj6UvQ==/R8WHe7pEBeqBhu8jTeXydg==/AAICoyitYqlxT7n6aZ0oMCGheFi4CXFp46AMUPZz1lMr_M9tr3_cjee1SHqxrOiVerMDLeyn9xzocZSKwi746Re8vNOtpNCAZjYABs_J0R25IHpvOc1HS8QHGgD5TgOJeS6gX100zdCIGeIlgZnkYj6UvVJWFNhSVhTiPE0=/00000/46016/00

Note: ID3 tags are not applicable for International (Germany)