From: Andre Noll <maan@tuebingen.mpg.de>
Date: Mon, 8 Sep 2014 20:38:35 +0000 (+0200)
Subject: oss: Avoid sound artefacts on some setups.
X-Git-Tag: v0.5.4~47^2
X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=commitdiff_plain;h=2ba45411ace62b419ce03a085491077deea38878

oss: Avoid sound artefacts on some setups.

Large buffers which result in short writes cause sound artefacts on
certain setups. For example, 22KHz audio on Linux/ALSA in OSS mode
is affected.

This patch caps the number of bytes to write to the maximum possible
value. This value is obtained through the SNDCTL_DSP_GETOSPACE ioctl.
---

diff --git a/oss_write.c b/oss_write.c
index 5b910742..35f7b628 100644
--- a/oss_write.c
+++ b/oss_write.c
@@ -189,6 +189,7 @@ static int oss_post_select(__a_unused struct sched *s, void *context)
 	size_t frames, bytes;
 	int ret;
 	char *data;
+	audio_buf_info abi;
 
 	ret = task_get_notification(wn->task);
 	if (ret < 0)
@@ -220,6 +221,15 @@ static int oss_post_select(__a_unused struct sched *s, void *context)
 	ret = 0;
 	if (!FD_ISSET(powd->fd, &s->wfds))
 		goto out;
+	/* get maximal number of bytes that can be written */
+	ret = ioctl(powd->fd, SNDCTL_DSP_GETOSPACE, &abi);
+	if (ret >= 0) {
+		size_t max_frames = abi.bytes / powd->bytes_per_frame;
+		if (max_frames == 0)
+			goto out;
+		/* cap number of frames to avoid sound artefacts */
+		frames = PARA_MIN(frames, max_frames);
+	}
 	ret = xwrite(powd->fd, data, frames * powd->bytes_per_frame);
 	if (ret < 0)
 		goto out;