a52 - Add slavepcm option

- Added slavepcm option to specify the slave PCM string explicitly
- Don't use plug but linear plugin for default slave.
  We need only the linear format conversion, and the channel/rate
  conversion should be avoided.

1 files changed, 17 insertions, 0 deletions

diff --git a/doc/a52.txt b/doc/a52.txt
index 236e64a..ce7ee33 100644
--- a/doc/a52.txt
+++ b/doc/a52.txt
@@ -17,6 +17,11 @@ In addition, the following options are available:
   The output PCM becomes "iec958:{CARD=$CARD}" with extra AESx
   settings.  When omitted, the default card is used.
 
+- The "slavepcm" option specifies a string of the slave PCM
+  explicitly.  This is useful if a device has no proper SPDIF
+  configuration (e.g. usb-audio), or if you want to pass your own PCM
+  definition.  This option is exclusive with "card" option.
+
 - The "rate" option specifies the input/output sample rate in HZ.
   The accepted rate is either 44100 or 48000.
   When omitted, 48000 is used.
@@ -43,6 +48,18 @@ bitrate 256kbps and output format S16_BE looks like below:
 		format S16_BE
 	}
 
+For using slavepcm option,
+
+	pcm.mypcm {
+		card 1
+		device 2
+	}
+
+	pcm.myout {
+		type a52
+		slavepcm "mypcm"
+	}
+
 
 The plugin reads always S16 format (i.e. native-endian) as input, so
 you'd need plug layer appropriately to covert it.