Subject: Re: [ecasound] ecasound 2.0.4 released!
From: Kai Vehmanen (k_AT_eca.cx)
Date: Thu Feb 14 2002 - 00:03:06 EET
On Thu, 24 Jan 2002, Tobiah wrote:
>> One possibility is that n-track uses different layout for 24bit
>> samples. Ecasound (and ALSA and most soundcards) handle 24bit samples
> That would be it then. With n-track I am able to make samples that
> really only use 3 bytes/sample. It can also pad on the right or
> left with a byte, but I like the savings in disk space.
I just committed the following change to CVS:
- changed: s24_le and s24_be sample formats are interpreted
as three-byte values, not as four-byte
24-in-32bits values as before; to access
unpacked 24bit data, use s32_le and s32_be
You should now be able to playback files saved in ntrack.
To access 24-in-32bits files, you can for instance do:
ecasound -f:s32_le,2,44100 -i typeselect,.raw,24bit_file.wav -o alsa
This works if the least significant byte has been zero padded. If the
align field is set correctly in the RIFF header (bits=24,
align=channel_count*3), ecasound can play these directly without need for
It's not possible to play 24bit files where the MS-byte is zero. On the
other hand these files are not standard RIFF PCM_WAVE files anymore.
> Because of the wBlockAlign field in the header,
> I don't object to padding 24bit samples to longs, but it is not
> clear from the above paragraph that this would be correct, and at least
> it suggests that a well behaved interpreter of wav files should catch the
> wBlockAlign size and be able to play true 3byte samples.
It's just that RIFF PCM_WAVE documents don't specify how the bits should
be physically laid out (ie. whether to pad extra msb or lsb bits).
Microsoft has issues a new RIFF-spec, WAVE_FORMAT_EXTENSIBLE, which tries
to solve these issues. Ecasound doesn't currently support it. Anyways, in
the extended format, valid sample bits are left-aligned and extra lsb bits
are padded to zero.
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