decoder/vorbis: scale and clip tremor-decoded samples to 15 bits

Tremor decoder is unusable since commit 2ee43c40. Sound is distorted to the point where it's nothing but noise. The data from vorbis_synthesis_pcmout() needs to be scaled and clipped for 16 bit sample size. For reference see http://lists.xiph.org/pipermail/tremor/2010-April/001642.html and http://lists.xiph.org/pipermail/vorbis/2006-October/026513.html. Signed-off-by: Marcin Jurkowski <marcin1j@gmail.com>

decoder/vorbis: scale and clip tremor-decoded samples to 15 bits
3b23cf02 · Marcin Jurkowski · Max Kellermann · 28e864e0 · 3b23cf02 · 3b23cf02
Commit 3b23cf02 authored Oct 29, 2017 by Marcin Jurkowski Committed by Max Kellermann Nov 03, 2017
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NEWS NEWS +2 -0

VorbisDecoderPlugin.cxx src/decoder/plugins/VorbisDecoderPlugin.cxx +15 -1

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--- a/NEWS
+++ b/NEWS
 ver 0.20.12 (not yet released)
 * input
  - curl: fix seeking
+* decoder
+  - vorbis: fix Tremor support
 * player
  - log message when decoder is too slow


--- a/src/decoder/plugins/VorbisDecoderPlugin.cxx
+++ b/src/decoder/plugins/VorbisDecoderPlugin.cxx
@@ -178,6 +178,20 @@ VorbisDecoder::SubmitInit()
 	client.Ready(audio_format, eos_granulepos > 0, duration);
 }

+#ifdef HAVE_TREMOR
+static inline int16_t tremor_clip_sample(int32_t x)
+{
+	x >>= 9;
+
+	if (x < INT16_MIN)
+		return INT16_MIN;
+	if (x > INT16_MAX)
+		return INT16_MAX;
+
+	return x;
+}
+#endif
+
 bool
 VorbisDecoder::SubmitSomePcm()
 {
@@ -197,7 +211,7 @@ VorbisDecoder::SubmitSomePcm()
 		auto *dest = &buffer[c];

 		for (size_t i = 0; i < n_frames; ++i) {
-			*dest = *src++;
+			*dest = tremor_clip_sample(*src++);
 			dest += channels;
 		}
 	}