[alsa-devel] Question about Conversion to S24_LE from S24_3LE
tiwai at suse.de
Mon Aug 20 08:47:47 CEST 2012
At Mon, 20 Aug 2012 14:57:51 +0900 (JST),
etsuko suzuki wrote:
> Hello, Takashi.
> > Hm, I guess your message didn't reach properly, or was filtered by some spam
> > Better to contact with Jaroslav (Cc'ed), who maintains alsa-devel ML.
> I contacted him in August 17.
> However, there is no reply yet.
Didn't you read his mail in Aug. 16?
You were in Cc.
> > > http://msdn.microsoft.com/en-us/windows/hardware/gg463006.aspx
> > >
> > > In this, I found the statement 'left-alinged'.
> > > (In 'Details about wValidBitsPerSample')
> > >
> > > I understood 'left-alinged' was 'LSB padding'.
> > > So I thought S24_LE was LSB padding.
> > No. S24_LE has the MSB padding of 8 bits in 32 bit container.
> That is, does it mean that this document is not correct?
> (I don't understand why this document differs from what you say.)
Well, Microsoft doesn't conquer the whole world yet.
Their definition isn't what we define for our purpose.
> (This PDF is the same as what was written before.
> The page is written on this.)
> On the 6 page of this PDF, it is written to like this.
> 'If wValidBitsPerSample is less than wBitsPerSample,
> then the actual
> PCM data is "left-aligned" within the container.
> The sample itself is justified most significant;
> all extra bits are at the least-significant
> portion of the container.
> All non-valid data bits must be set to 0.'
> In S24_LE, I think 'wBitsPerSample' indicates
> 'the container size'(=32) and
> 'wValidBitsPerSample' indicates 'the bit of actual valid data'(=24).
You _think_ but you utterly misunderstand the terms.
ALSA S24 is not what you think. S24 is a special format, 3 bytes LSB
in 4 bytes container. This _is_ the definition. There is no such a
format in MS's WAV definition.
wValidBitsPerSample is rather corresponding to hw_params ms_bits
> It was written that Microsoft has defined
> the new structure 'WAVE_FORMAT_EXTENSIBLE'(FORMAT_CODE:0xFFFE).
> (On the 4 page of this PDF.)
> I think that the new structure should be used
> in this(the container size > the bit of actual valid data) case.
> But the structure recording
> by arecord was 'WAVE_FORMAT_PCM'(FORMAT_CODE:0x0001).
> > % od -t x4 ubuntu_rec_S24_LE_48000.wav
> > 0000000 46464952 003a9824 45564157 20746d66
> > 0000010 00000010 00020001 0000bb80 0005dc00
> ^^^^ 0x0001:WAVE_FORMAT_PCM
> (The 'FORMAT_CODE' is written in this page.
> Why does ALSA NOT use the new structure?
Because it's new, and no one cared such a thing.
> Has ALSA corresponded to the new structure?
Please send a fix patch if you'd like to improve :)
More information about the Alsa-devel