Re: [Red5] OT - Spark compression ratio for live audio

Fri, 21 Jul 2006 07:28:19 -0700

Spark is the video codec, not the audio codec. Audio encoded with the Flash player (i.e. a live stream recorded by Red5) uses the Nelly Moser ASAO codec. (Search the list archives for lots of Nelly Moser complaints.) I haven't looked into the innards of Nelly Moser, but the following info seems reasonable (from http://www.progettosinergia.com/flashvideo/flashvideoblog.htm):

Every ASAO packet are compressed of a 1 to 8 ratio. The original 256 audio samples are trasformed in frequency domain. Then is applyed an audio masking control to reduce the number of significant coefficients. A number of high amplitude frequency coefficients remained is finally quantized and Huffman encoded to reduce entropy and redundancies.

Not that this information is much help... since your only other option is MP3 audio (for on-demand videos only). I guess a better question is, why does the compression ratio matter? What exactly are you trying to do / figure out?


Rob


On Jul 19, 2006, at 10:45 PM, electroteque wrote:

Hi sorry, this is a little off topic, ive been trying to track down 
what the compression ratio for the microphone audio is and if its the 
same spark codec as for video. Its a shame it only does mono, i have 
tracked down an article saying its 2.5:1 , however it contradicts that 
on another article with its conversions from kHz to bps. Let me know 
thanks.

Dan

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