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  1. #1
    Beesley, S
    Guest

    bit rate limiting

    I am a bit confused by this. I understand what the limit setting essentially does. However, the help suggests that if (for example) I set the limit at 320 and I have a 128K WMA file that the result will be a 320K stream because of the decoding / encoding to MP3. Is this true or will the result never be larger than the original file? Also, what happens with "no limit"?

    In fact, can somebody describe how the Slimserver interacts with the decoding components - e.g. Slim to WMADEC to LAME to SB. What do all the bits do? I have to say it seems pretty clever how Slim must be interacting with LAME for WMA files...

    Thanks

  2. #2
    NOT a Slim Devices Employee kdf's Avatar
    Join Date
    Apr 2005
    Posts
    9,493

    bit rate limiting

    Quoting "Beesley, S" <sbeesley (AT) dsl (DOT) pipex.com>:

    > I am a bit confused by this. I understand what the limit setting essentially
    > does. However, the help suggests that if (for example) I set the limit at 320
    > and I have a 128K WMA file that the result will be a 320K stream because of
    > the decoding / encoding to MP3. Is this true or will the result never be
    > larger than the original file? Also, what happens with "no limit"?


    by default, a wired squeezebox and softsqueeze will be set at 'no limit' this
    means mp3 plays untouched as mp3 and all other formats are decompressed to WAV
    or AIFF and played. If you have a limit set, (wireless defaults to 320kbps),
    then any mp3 t will play native and all other formats are converted to WAV,
    then back down to 320kbps MP3. If you set a lower bitrate limit, then the
    server checks the bitrate of mp3 files, and will re-encode any files that are
    of a higher bitrate than the limit, playing lower limit files untouched.
    When/if other native formats are available on the suqeezebox hardware, bitrate
    limiting will also choose teh best format for output in order to meet the limit
    requirements.


    > In fact, can somebody describe how the Slimserver interacts with the decoding
    > components - e.g. Slim to WMADEC to LAME to SB. What do all the bits do? I
    > have to say it seems pretty clever how Slim must be interacting with LAME for
    > WMA files...


    its called STDOUT and STDIN. these are standardised ways of hading input and
    output of data. Most systems can then take this sream of data and "redirect"
    or "pipe" it to another programme with STDIN abilities. Thus, a WMA file is
    played by wmadec, which puts out WAV data that is sent to LAME, which spits
    out 320kbps MP3. the mp3 data is then sent on the fly to the squeezebox,
    decoded and heard.
    -kdf

  3. #3
    Beesley, S
    Guest

    bit rate limiting

    > by default, a wired squeezebox and softsqueeze will be set at 'no limit'
    > this
    > means mp3 plays untouched as mp3 and all other formats are decompressed to
    > WAV
    > or AIFF and played. If you have a limit set, (wireless defaults to
    > 320kbps),
    > then any mp3 t will play native and all other formats are converted to
    > WAV,
    > then back down to 320kbps MP3. If you set a lower bitrate limit, then the
    > server checks the bitrate of mp3 files, and will re-encode any files that
    > are
    > of a higher bitrate than the limit, playing lower limit files untouched.
    > When/if other native formats are available on the suqeezebox hardware,
    > bitrate
    > limiting will also choose teh best format for output in order to meet the
    > limit
    > requirements.
    >

    Thanks. I'm still unclear. When playing WMA you way it converts to WAV, but
    at what bit rate. If I have a 96K WMA and limit set to 128K, then what
    bitrate WAV and MP3 gets produced?

  4. #4
    NOT a Slim Devices Employee kdf's Avatar
    Join Date
    Apr 2005
    Posts
    9,493

    bit rate limiting

    Quoting "Beesley, S" <sbeesley (AT) dsl (DOT) pipex.com>:

    >
    > > by default, a wired squeezebox and softsqueeze will be set at 'no limit'
    > > this
    > > means mp3 plays untouched as mp3 and all other formats are decompressed to
    > > WAV
    > > or AIFF and played. If you have a limit set, (wireless defaults to
    > > 320kbps),
    > > then any mp3 t will play native and all other formats are converted to
    > > WAV,
    > > then back down to 320kbps MP3. If you set a lower bitrate limit, then the
    > > server checks the bitrate of mp3 files, and will re-encode any files that
    > > are
    > > of a higher bitrate than the limit, playing lower limit files untouched.
    > > When/if other native formats are available on the suqeezebox hardware,
    > > bitrate
    > > limiting will also choose teh best format for output in order to meet the
    > > limit
    > > requirements.
    > >

    > Thanks. I'm still unclear. When playing WMA you way it converts to WAV, but
    > at what bit rate. If I have a 96K WMA and limit set to 128K, then what
    > bitrate WAV and MP3 gets produced?


    WAV is played back as 44.1kHz, 16-bit/sample, stereo. This is (44100*16*2) 1411
    kbps.

    96kbps WMA is one of those examples where things, by necessity have to be an
    exception. The server should be forcing MP3 output whenever the bitrate limit
    is anything BUT 'no limit'. Thus you should get a 128kbps stream. The only
    native format supported that can do low bitrates is mp3, so that format is
    forced. bitrate is set to the bitrate limit, since lower bitrates require more
    cpu resources.

    -kdf

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