Archive for the ‘Audio’ Category

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Variety of lossless audio codecs

Saturday, September 23rd, 2006

There are currently 14 lossless audio codecs mentioned on MultiMedia Wiki page (look here for further links):

  • Proprietary (Apple Lossless, Meridian Lossless Packing, Real Lossless, WMA Lossless)
  • Closed source (LA, LPAC, LTAC, OptimFROG, RK Audio)
  • Open source (Bonk, FLAC, MPEG-4 ALS, Monkey’s Audio, Shorten, TrueAudio, WavPack)

FFmpeg currently has decoders for Bonk, FLAC, Shorten, TrueAudio and Apple Lossless. So, there are at least MPEG-4 ALS, Monkey’s Audio and WavPack decoders can be added.

I will work on WavPack decoder and ALS (I hope standard will appear soon). What about Monkey’s Audio? Yes, it’s popular but it has following difficulties for implementation:

  1. It has incredibly large  frame sizes (it may be more than one million samples) while competitors stick around 64k or less (hence the compression gain for MA). Current FFmpeg design cannot handle such frames.
  2. Source code is a mess – for almost every action there are at least several if(ver >= …) or if(ver< ...). Format is too unstable for me.

Well, I still hope it will be implemented some day.

Posted in Lossless Audio | 7 Comments »

TrueSpeech – 97% complete

Friday, December 30th, 2005

Now my TrueSpeech decoder decodes compressed audio almost as well as original decoder. Why not 100% complete? It decodes audio slightly different from original decoder, so it may take some time in future to make my decoder identical.

I hope to see it in FFmpeg source tree soon.

Posted in Audio, TrueSpeech | 2 Comments »

TrueSpeech – Some Information

Wednesday, October 12th, 2005

Here are main differences between TrueSpeech and G.723:
1) One bitrate (8 Kb/s) vs. two bitrates (6.3 and 5.3 Kb/s)
2) Lower complexity (TrueSpeech uses 8-point LPC, G.723 – 10-point LPC)

Frame structure is also differs, TrueSpeech packs everything into 32 byte frame where some values are spread between different doublewords (3d bit is in one dword, 2nd is in another one).

Posted in Audio, TrueSpeech | Comments Closed

TrueSpeech – Old Audio Codec

Tuesday, October 4th, 2005

DSP Group TrueSpeech audio codec is rumored to be a relative to ITU G.723. That may be partly true: DSP Group took part in developing G.723, but if you study recommendation G.723, you’ll see that there are two methods used in this rec., and they differ.
Studies showed that TrueSpeech may be one of predecessors of G.723 – it is simplier, needs higher bitrate than G.723 and such. But I hope to use some ideas to reconstruct TrueSpeech decoder using methods from G.723.

Posted in Audio, TrueSpeech | 1 Comment »

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