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authorMax Kellermann <max@duempel.org>2008-10-23 16:58:38 +0200
committerMax Kellermann <max@duempel.org>2008-10-23 16:58:38 +0200
commit2cc2420f8cb71be62851273fc4ce9bf5223155f6 (patch)
tree7cdd34de2e502e2703910de2fddc5d01f3557507
parentbf5774edbd29ecf4d14119e04acf65d16dd762fa (diff)
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mp3: send 24 bit PCM data
libmad produces samples of more than 24 bit. Rounding that down to 16 bits using dithering makes those people lose quality who have a 24 bit capable sound device. Send 24 bit PCM data, and let the receiver decide whether to apply 16 bit dithering.
Diffstat (limited to '')
-rw-r--r--src/inputPlugins/mp3_plugin.c87
1 files changed, 24 insertions, 63 deletions
diff --git a/src/inputPlugins/mp3_plugin.c b/src/inputPlugins/mp3_plugin.c
index 158a152cd..a0de30ba7 100644
--- a/src/inputPlugins/mp3_plugin.c
+++ b/src/inputPlugins/mp3_plugin.c
@@ -51,77 +51,39 @@ enum muteframe {
static int gaplessPlaybackEnabled;
-/* this is stolen from mpg321! */
-struct audio_dither {
- mad_fixed_t error[3];
- mad_fixed_t random;
-};
-
-static unsigned long prng(unsigned long state)
-{
- return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL;
-}
-
-static int16_t audio_linear_dither(mad_fixed_t sample,
- struct audio_dither *dither)
+static inline int32_t
+mad_fixed_to_24_sample(mad_fixed_t sample)
{
- mad_fixed_t output, mask, rnd;
-
enum {
- bits = 16,
- scalebits = MAD_F_FRACBITS + 1 - bits,
+ bits = 24,
MIN = -MAD_F_ONE,
MAX = MAD_F_ONE - 1
};
- sample += dither->error[0] - dither->error[1] + dither->error[2];
-
- dither->error[2] = dither->error[1];
- dither->error[1] = dither->error[0] / 2;
-
- output = sample + (1L << (MAD_F_FRACBITS + 1 - bits - 1));
-
- mask = (1L << scalebits) - 1;
+ /* round */
+ sample = sample + (1L << (MAD_F_FRACBITS - bits));
- rnd = prng(dither->random);
- output += (rnd & mask) - (dither->random & mask);
+ /* clip */
+ if (sample > MAX)
+ sample = MAX;
+ else if (sample < MIN)
+ sample = MIN;
- dither->random = rnd;
-
- if (output > MAX) {
- output = MAX;
-
- if (sample > MAX)
- sample = MAX;
- } else if (output < MIN) {
- output = MIN;
-
- if (sample < MIN)
- sample = MIN;
- }
-
- output &= ~mask;
-
- dither->error[0] = sample - output;
-
- return (int16_t)(output >> scalebits);
+ /* quantize */
+ return sample >> (MAD_F_FRACBITS + 1 - bits);
}
-static unsigned dither_buffer(int16_t *dest0, const struct mad_synth *synth,
- struct audio_dither *dither,
- unsigned int start, unsigned int end,
- unsigned int num_channels)
+static void
+mad_fixed_to_24_buffer(int32_t *dest, const struct mad_synth *synth,
+ unsigned int start, unsigned int end,
+ unsigned int num_channels)
{
- int16_t *dest = dest0;
unsigned int i, c;
for (i = start; i < end; ++i) {
for (c = 0; c < num_channels; ++c)
- *dest++ = audio_linear_dither(synth->pcm.samples[c][i],
- dither);
+ *dest++ = mad_fixed_to_24_sample(synth->pcm.samples[c][i]);
}
-
- return dest - dest0;
}
/* end of stolen stuff from mpg321 */
@@ -145,7 +107,7 @@ typedef struct _mp3DecodeData {
struct mad_synth synth;
mad_timer_t timer;
unsigned char readBuffer[READ_BUFFER_SIZE];
- int16_t outputBuffer[MP3_DATA_OUTPUT_BUFFER_SIZE];
+ int32_t outputBuffer[MP3_DATA_OUTPUT_BUFFER_SIZE];
float totalTime;
float elapsedTime;
enum muteframe muteFrame;
@@ -164,7 +126,6 @@ typedef struct _mp3DecodeData {
unsigned long bitRate;
struct decoder *decoder;
InputStream *inStream;
- struct audio_dither dither;
enum mad_layer layer;
} mp3DecodeData;
@@ -187,7 +148,6 @@ static void initMp3DecodeData(mp3DecodeData * data, struct decoder *decoder,
data->decoder = decoder;
data->inStream = inStream;
data->layer = 0;
- memset(&(data->dither), 0, sizeof(struct audio_dither));
mad_stream_init(&data->stream);
mad_stream_options(&data->stream, MAD_OPTION_IGNORECRC);
@@ -933,10 +893,11 @@ mp3Read(mp3DecodeData * data, ReplayGainInfo ** replayGainInfo)
i += num_samples;
- num_samples = dither_buffer(data->outputBuffer,
- &data->synth, &data->dither,
- i - num_samples, i,
- MAD_NCHANNELS(&(data->frame).header));
+ mad_fixed_to_24_buffer(data->outputBuffer,
+ &data->synth,
+ i - num_samples, i,
+ MAD_NCHANNELS(&(data->frame).header));
+ num_samples *= MAD_NCHANNELS(&(data->frame).header);
cmd = decoder_data(decoder, data->inStream,
data->inStream->seekable,
@@ -1022,7 +983,7 @@ mp3Read(mp3DecodeData * data, ReplayGainInfo ** replayGainInfo)
static void initAudioFormatFromMp3DecodeData(mp3DecodeData * data,
struct audio_format * af)
{
- af->bits = 16;
+ af->bits = 24;
af->sample_rate = (data->frame).header.samplerate;
af->channels = MAD_NCHANNELS(&(data->frame).header);
}