[Vorbis-dev] Vorbis for digital radio at low bitrates

[Ralph Giles]

On 22 March 2010 06:58, Feilen, Michael <michael.feilen at tum.de> wrote:

> My name is Michael Feilen and I've been working on Digital Radio Mondiale (DRM) transmitters and receivers for quite a while now. DRM uses HE-AACv2 by Dolby to encode the audio content (see http://www.drm.org/uploads/media/es_201980v030101p.pdf - pages 23 ff). As I think Vorbis is an excellent alternative, I'd like to implement and define an interface for Vorbis encoded audio as unofficial amendment to the standard and I would be grateful if one of you could help me with the integration.

Sounds great; thanks for supporting free formats!

> The encoder requirements for DRM(+) are:
> * Support for 12 kHz, 24 kHz and 48 kHz sample rates.

This is no problem, although the reference encoder is tuned for 44/48
kHz and will perform better there than at 12 kHz.

> * A frame-format (transform length) of 960 samples per frame. At the moment, the codec seems only to support transform lengths of powers of two (e.g. 512, 1024, ...).

It's worse than that; Vorbis uses a mix of two different transform
lengths. There's no way this requirement can be met by a Vorbis
implementation. Can you explain why this is important?

> * Fixed bitrates from 12 kBit/s to ~128 kBit/s.

This is no problem. The reference encoder supports ABR/CBR output.

 -r