alsa: Improve documentation of struct private_alsa_write_data.

Remove the stale reference to writer node groups and explain how
sample_rate and channel count are determined.

diff --git a/alsa_write.c b/alsa_write.c
index 0824640b9560d72a1eb886a355c3f07e5271681f..53854e08c012dd7952df4d94ce50dae987dc004a 100644 (file)
--- a/alsa_write.c
+++ b/alsa_write.c
@@ -34,16 +34,21 @@ struct private_alsa_write_data {
        snd_pcm_t *handle;
        /** Determined and set by alsa_init(). */
        int bytes_per_frame;
-       /**
-        * The sample rate given by command line option or the decoder
-        * of the writer node group.
+       /*
+        * If the sample rate is not given at the command line and no wav
+        * header was detected, the btr exec mechanism is employed to query the
+        * ancestor buffer tree nodes for this information. In a typical setup
+        * the decoder passes the sample rate back to the alsa writer.
+        *
+        *  \sa \ref btr_exec_up().
         */
        unsigned sample_rate;
-       snd_pcm_format_t sample_format;
-       /**
-        * The number of channels, given by command line option or the
-        * decoder of the writer node group.
+       /*
+        * The sample format (8/16 bit, signed/unsigned, little/big endian) is
+        * determined in the same way as the \a sample_rate.
         */
+       snd_pcm_format_t sample_format;
+       /* The number of channels, again determined like \a sample_rate. */
        unsigned channels;
        struct timeval drain_barrier;
        /* File descriptor for select(). */