[tremor] Start up time / overhead

[Nicolas Pitre]

On Wed, 18 Sep 2002, David Hembrow wrote:

> The problems I have encountered are as follows:
> 
> 1. There is considerable overhead in the format, and our samples are short
>    (individual words which the software puts together). As a result, the
>    output file size is such that the bit rate works out on average as
>    effectively more like 28kb/s. Is there a way of reducing the size of
>    this overhead ?

The default header on encoded files is rather large.  There is a tool called 
rehuff that significantly reduces header size.  This is especially handy for 
multiple small files like you have.

I'm not sure where to find the latest version of rehuff, but here's a 
reference to start with:

        http://www.xiph.org/archives/vorbis-dev/200207/0210.html

> 2. There is also a time overhead in that the samples take a considerable
>    time to start playing. As our software has to speak many samples back
>    to back, this produces un-natural pauses between words. Is there a way
>    of decreasing this start up time overhead per sample ?

Maybe with the parsing of smaller headers you'll reduce that startup time.

> 3. In comparison with 11kHz ADPCM, any 8kHz format sounds lacking due to
>    the lack of sibilance. If I specify --resample 11025, oggenc requires
>    that I increase the -b argument to 12, and produces around 16kb/s
>    output. The resulting file is too time consuming for our slow processor
>    to decode in real time. Absolute sound quality is not nearly as important
>    to us as file size and decoding speed, but is there a way of encoding
>    vorbis so that I preserve the sibilance without increasing decoding time
>    or output file size ?

You could try my latest patch which saves about 12% on decoding time on a
StrongARM.  This might be just enough for your processor to reach real time
decoding.

> Also, I am using the ARM ADS v1.1. I have converted the inline assembler
> routines in arm_arm.h to compile with the inline assembler of the ADS.
> I have seen discussion of using MSVC with this header file, and suspect
> that what I have now is likely to be more similar to what MSVC would
> require. I can contribute this if it is wanted.

If you post it here people will certainly make good use of it.

<p>Nicolas

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