Alsa fixes and cleanups.

This patch

- replaces the unused E_SND_PCM_INFO error by E_PHYSICAL_WIDTH,

- checks the return value of snd_pcm_format_physical_width() and returns
  -E_PHYSICAL_WIDTH if this causes bytes_per_frame being non-positive,

- introduces an upper bound for the start threshold. Without that
  change, playback could be delayed by several seconds on some alsa
  configurations (problem pointed out by Johannes Wörner, thanks).

- does not return early on input errors which could cause the last
  part of the audio stream being skipped.

- avoids calling snd_pcm_writei() with a frame count of zero which
  could happen with the old code in case there's more than zero but
  less than a full frame of audio data available.

- cleans up the documentation of struct private_alsa_write_data

diff --git a/alsa_write.c b/alsa_write.c
index e070399d3f0dbf0145fa39e090b46d5f7c6cbb63..0bb3de38d6a06dd81562a95e518453fd666e4991 100644 (file)
--- a/alsa_write.c
+++ b/alsa_write.c
@@ -29,19 +29,19 @@
 /** always use 16 bit little endian */
 #define FORMAT SND_PCM_FORMAT_S16_LE
 
-/** data specific to the alsa writer */
+/** Data specific to the alsa writer. */
 struct private_alsa_write_data {
-       /** the alsa handle */
+       /** The alsa handle */
        snd_pcm_t *handle;
-       /** determined and set by alsa_open() */
-       size_t bytes_per_frame;
-       /** don't write anything until this time */
+       /** Determined and set by alsa_open(). */
+       int bytes_per_frame;
+       /** Don't write anything until this time. */
        struct timeval next_chunk;
-       /** the return value of snd_pcm_hw_params_get_buffer_time_max() */
+       /** The approximate maximum buffer duration in us. */
        unsigned buffer_time;
        /**
-        * the samplerate given by command line option or the decoder
-        * of the writer node group
+        * The samplerate given by command line option or the decoder
+        * of the writer node group.
         */
        unsigned samplerate;
        /**
@@ -101,7 +101,8 @@ static int alsa_init(struct private_alsa_write_data *pad,
        if (buffer_size < 1)
                start_threshold = 1;
        else
-               start_threshold = buffer_size;
+               start_threshold = PARA_MIN(buffer_size,
+                       (snd_pcm_uframes_t)pad->samplerate);
        if (snd_pcm_sw_params_set_start_threshold(pad->handle, swparams,
                        start_threshold) < 0)
                return -E_START_THRESHOLD;
@@ -113,6 +114,8 @@ static int alsa_init(struct private_alsa_write_data *pad,
                PARA_WARNING_LOG("unable to install sw params\n");
        pad->bytes_per_frame = snd_pcm_format_physical_width(FORMAT)
                * pad->channels / 8;
+       if (pad->bytes_per_frame <= 0)
+               return -E_PHYSICAL_WIDTH;
        PARA_INFO_LOG("bytes per frame: %zu\n", pad->bytes_per_frame);
        if (snd_pcm_nonblock(pad->handle, 1))
                PARA_ERROR_LOG("failed to set nonblock mode\n");
@@ -168,6 +171,10 @@ static int alsa_write_post_select(__a_unused struct sched *s,
        struct timeval tv;
        snd_pcm_sframes_t ret;
 
+       if (*wng->input_error < 0 && (!pad->handle || bytes < pad->bytes_per_frame)) {
+               wn->written = *wng->loaded;
+               return *wng->input_error;
+       }
        if (!bytes) /* no data available */
                goto out;
        if (tv_diff(now, &pad->next_chunk, NULL) < 0)
@@ -178,6 +185,8 @@ static int alsa_write_post_select(__a_unused struct sched *s,
                        return err;
        }
        frames = bytes / pad->bytes_per_frame;
+       if (!frames) /* less than a single frame available */
+               goto out;
        ret = snd_pcm_writei(pad->handle, data, frames);
        if (ret == -EPIPE) {
                PARA_WARNING_LOG("EPIPE\n");
@@ -195,15 +204,11 @@ static int alsa_write_post_select(__a_unused struct sched *s,
                wn->written += ret * pad->bytes_per_frame;
        if (ret == frames) /* we wrote everything, try again immediately */
                pad->next_chunk = *now;
-       else {
-               ms2tv(pad->buffer_time / pad->bytes_per_frame / 1000, &tv);
+       else { /* wait until 50% buffer space is available */
+               ms2tv(pad->buffer_time / 2000, &tv);
                tv_add(now, &tv, &pad->next_chunk);
        }
 out:
-       if (*wng->input_error < 0) {
-               wn->written = *wng->loaded;
-               return *wng->input_error;
-       }
        return 1;
 }
 

diff --git a/error.h b/error.h
index 17f3703f41d20217540463f9fea64fa75b159cd2..604152233b003e44667f7b69fc2515c74b26f480 100644 (file)
--- a/error.h
+++ b/error.h
@@ -396,7 +396,7 @@ extern const char **para_errlist[];
        PARA_ERROR(BAD_PERIOD, "can not use period equal to buffer size"), \
        PARA_ERROR(ALSA_WRITE, "alsa write error"), \
        PARA_ERROR(PCM_OPEN, "unable to open pcm"), \
-       PARA_ERROR(SND_PCM_INFO, "pcm info error"), \
+       PARA_ERROR(PHYSICAL_WIDTH, "unable to determine bytes per frame"), \
        PARA_ERROR(GET_BUFFER_TIME, "snd_pcm_hw_params_get_buffer_time_max() failed"), \
        PARA_ERROR(SET_BUFFER_TIME, "snd_pcm_hw_params_set_buffer_time_near() failed"), \
        PARA_ERROR(SET_RATE, "snd_pcm_hw_params_set_rate_near failed"), \