emergency-cap-profiles — archive

[Art Botterell]

As you're aware, one of the comments we've received on the draft profile has to do with the audio encoding format or formats supported for recorded and streaming audio, primarily for EAS. This is important because whatever format or formats are specified in the profile will, presumably, become mandatory for any next-generation EAS implementation. The ECIG (a semi-formal working group of some the major EAS equipment manufacturers) recommended two audio formats: WAV and MP3. The WAV format is non-proprietary but requires much more bandwidth than compressed formats such as MP3. The MP3 format is more bandwidth-efficient than WAV, but it's subject to patent restrictions and would require implementers to enter into licensing agreements and pay fees. Commenting on the Profile draft (# 69 in our current issues list), Tom Wood of Digital Alert Systems, an EAS manufacturer and ECIG member, suggested that the non-proprietary Ogg/Vorbis encoding be added to the list of acceptable formats. He argued that this format can provide audio quality and data compression comparable to MP3 but without patent restrictions. He also suggested the addition of the Ogg/Theora format for video. A note on the nomenclature: "Ogg" refers to a file format that can be used to store multimedia content in a number of encodings. "Vorbis," "Theora" and also "Speex" (see below) refer to encoding techniques for encoding analog content such as audio or video in digital form. In the case of fixed-length recordings an encoded bitstream can be packaged in an Ogg-format file; thus, for example, the label "ogg/vorbis." However, in a streaming-media application the encoding frequently is transmitted without the Ogg encapsulation, e.g., in an RTP-based streaming system such as IceCast or ShoutCast. In reviewing the literature on the Vorbis encoding it came to my attention that there is another codec in the same series of open-source, non-proprietary formats, one known as "Speex," that is more highly optimized for voice transmission over limited bandwidth links (2-44 kbps). The Speex webside explains that "Vorbis is mostly aimed at compressing music and audio in general, which Speex targets speech only. For that reason Speex can achieve much better results than Vorbis on speech, typically 2-4 times higher compression at equal quality." A few links for reference: * The Speex website: