lfe-filter: Add rewind support

Store current filter state at every normal block process.
When a rewind happens, rewind back to the nearest saved state,
then calculate forward to the actual sample position.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>

src/pulsecore/filter/lfe-filter.c

@@ -23,9 +23,20 @@
 
 #include "lfe-filter.h"
 #include <pulse/xmalloc.h>
+#include <pulsecore/flist.h>
+#include <pulsecore/llist.h>
 #include <pulsecore/filter/biquad.h>
 #include <pulsecore/filter/crossover.h>
 
+struct saved_state {
+    PA_LLIST_FIELDS(struct saved_state);
+    pa_memchunk chunk;
+    int64_t index;
+    struct lr4 lr4[PA_CHANNELS_MAX];
+};
+
+PA_STATIC_FLIST_DECLARE(lfe_state, 0, pa_xfree);
+
 /* An LR4 filter, implemented as a chain of two Butterworth filters.
 
    Currently the channel map is fixed so that a highpass filter is applied to all
@@ -35,24 +46,37 @@
 */
 
 struct pa_lfe_filter {
+    int64_t index;
+    PA_LLIST_HEAD(struct saved_state, saved);
     float crossover;
     pa_channel_map cm;
     pa_sample_spec ss;
+    size_t maxrewind;
     bool active;
     struct lr4 lr4[PA_CHANNELS_MAX];
 };
 
-pa_lfe_filter_t * pa_lfe_filter_new(const pa_sample_spec* ss, const pa_channel_map* cm, float crossover_freq) {
+static void remove_state(pa_lfe_filter_t *f, struct saved_state *s) {
+    PA_LLIST_REMOVE(struct saved_state, f->saved, s);
+    pa_memblock_unref(s->chunk.memblock);
+    pa_xfree(s);
+}
+
+pa_lfe_filter_t * pa_lfe_filter_new(const pa_sample_spec* ss, const pa_channel_map* cm, float crossover_freq, size_t maxrewind) {
 
     pa_lfe_filter_t *f = pa_xnew0(struct pa_lfe_filter, 1);
     f->crossover = crossover_freq;
     f->cm = *cm;
     f->ss = *ss;
+    f->maxrewind = maxrewind;
     pa_lfe_filter_update_rate(f, ss->rate);
     return f;
 }
 
 void pa_lfe_filter_free(pa_lfe_filter_t *f) {
+    while (f->saved)
+        remove_state(f, f->saved);
+
     pa_xfree(f);
 }
 
@@ -60,26 +84,61 @@ void pa_lfe_filter_reset(pa_lfe_filter_t *f) {
     pa_lfe_filter_update_rate(f, f->ss.rate);
 }
 
-pa_memchunk * pa_lfe_filter_process(pa_lfe_filter_t *f, pa_memchunk *buf) {
+static void process_block(pa_lfe_filter_t *f, pa_memchunk *buf, bool store_result) {
     int samples = buf->length / pa_frame_size(&f->ss);
 
-    if (!f->active)
-        return buf;
+    void *garbage = store_result ? NULL : pa_xmalloc(buf->length);
+
     if (f->ss.format == PA_SAMPLE_FLOAT32NE) {
         int i;
         float *data = pa_memblock_acquire_chunk(buf);
         for (i = 0; i < f->cm.channels; i++)
-            lr4_process_float32(&f->lr4[i], samples, f->cm.channels, &data[i], &data[i]);
+            lr4_process_float32(&f->lr4[i], samples, f->cm.channels, &data[i], garbage ? garbage : &data[i]);
         pa_memblock_release(buf->memblock);
     }
     else if (f->ss.format == PA_SAMPLE_S16NE) {
         int i;
         short *data = pa_memblock_acquire_chunk(buf);
         for (i = 0; i < f->cm.channels; i++)
-            lr4_process_s16(&f->lr4[i], samples, f->cm.channels, &data[i], &data[i]);
+            lr4_process_s16(&f->lr4[i], samples, f->cm.channels, &data[i], garbage ? garbage : &data[i]);
         pa_memblock_release(buf->memblock);
     }
     else pa_assert_not_reached();
+
+    pa_xfree(garbage);
+    f->index += samples;
+}
+
+pa_memchunk * pa_lfe_filter_process(pa_lfe_filter_t *f, pa_memchunk *buf) {
+    struct saved_state *s, *s2;
+    void *data;
+
+    if (!f->active)
+        return buf;
+
+    /* Remove old states (FIXME: we could do better than searching the entire array here?) */
+    PA_LLIST_FOREACH_SAFE(s, s2, f->saved)
+        if (s->index + (int64_t) (s->chunk.length / pa_frame_size(&f->ss) + f->maxrewind) < f->index)
+            remove_state(f, s);
+
+    /* Insert our existing state into the flist */
+    if ((s = pa_flist_pop(PA_STATIC_FLIST_GET(lfe_state))) == NULL)
+        s = pa_xnew(struct saved_state, 1);
+    PA_LLIST_INIT(struct saved_state, s);
+
+    /* TODO: This actually memcpys the entire chunk into a new allocation, because we need to retain the original
+       in case of rewinding. Investigate whether this can be avoided. */
+    data = pa_memblock_acquire_chunk(buf);
+    s->chunk.memblock = pa_memblock_new_malloced(pa_memblock_get_pool(buf->memblock), pa_xmemdup(data, buf->length), buf->length);
+    s->chunk.length = buf->length;
+    s->chunk.index = 0;
+    pa_memblock_release(buf->memblock);
+
+    s->index = f->index;
+    memcpy(s->lr4, f->lr4, sizeof(struct lr4) * f->cm.channels);
+    PA_LLIST_PREPEND(struct saved_state, f->saved, s);
+
+    process_block(f, buf, true);
     return buf;
 }
 
@@ -87,6 +146,10 @@ void pa_lfe_filter_update_rate(pa_lfe_filter_t *f, uint32_t new_rate) {
     int i;
     float biquad_freq = f->crossover / (new_rate / 2);
 
+    while (f->saved)
+        remove_state(f, f->saved);
+
+    f->index = 0;
     f->ss.rate = new_rate;
     if (biquad_freq <= 0 || biquad_freq >= 1) {
         pa_log_warn("Crossover frequency (%f) outside range for sample rate %d", f->crossover, new_rate);
@@ -99,3 +162,37 @@ void pa_lfe_filter_update_rate(pa_lfe_filter_t *f, uint32_t new_rate) {
 
     f->active = true;
 }
+
+void pa_lfe_filter_rewind(pa_lfe_filter_t *f, size_t amount) {
+    struct saved_state *i, *s = NULL;
+    size_t samples = amount / pa_frame_size(&f->ss);
+    f->index -= samples;
+
+    /* Find the closest saved position */
+    PA_LLIST_FOREACH(i, f->saved) {
+        if (i->index > f->index)
+            continue;
+        if (s == NULL || i->index > s->index)
+            s = i;
+    }
+    if (s == NULL) {
+        pa_log_debug("Rewinding LFE filter %lu samples to position %lli. No saved state found", samples, (long long) f->index);
+        pa_lfe_filter_update_rate(f, f->ss.rate);
+        return;
+    }
+    pa_log_debug("Rewinding LFE filter %lu samples to position %lli. Found saved state at position %lli",
+        samples, (long long) f->index, (long long) s->index);
+    memcpy(f->lr4, s->lr4, sizeof(struct lr4) * f->cm.channels);
+
+    /* now fast forward to the actual position */
+    if (f->index > s->index) {
+        pa_memchunk x = s->chunk;
+        x.length = (f->index - s->index) * pa_frame_size(&f->ss);
+        if (x.length > s->chunk.length) {
+            pa_log_error("Hole in stream, cannot fast forward LFE filter");
+            return;
+        }
+        f->index = s->index;
+        process_block(f, &x, false);
+    }
+}

src/pulsecore/filter/lfe-filter.h

@@ -25,13 +25,14 @@
 #include <pulse/sample.h>
 #include <pulse/channelmap.h>
 #include <pulsecore/memchunk.h>
-
+#include <pulsecore/memblockq.h>
 
 typedef struct pa_lfe_filter pa_lfe_filter_t;
 
-pa_lfe_filter_t * pa_lfe_filter_new(const pa_sample_spec* ss, const pa_channel_map* cm, float crossover_freq);
+pa_lfe_filter_t * pa_lfe_filter_new(const pa_sample_spec* ss, const pa_channel_map* cm, float crossover_freq, size_t maxrewind);
 void pa_lfe_filter_free(pa_lfe_filter_t *);
 void pa_lfe_filter_reset(pa_lfe_filter_t *);
+void pa_lfe_filter_rewind(pa_lfe_filter_t *, size_t amount);
 pa_memchunk * pa_lfe_filter_process(pa_lfe_filter_t *filter, pa_memchunk *buf);
 void pa_lfe_filter_update_rate(pa_lfe_filter_t *, uint32_t new_rate);
 

src/pulsecore/resampler.c

@@ -419,7 +419,8 @@ pa_resampler* pa_resampler_new(
     if (lfe_filter_required) {
         pa_sample_spec wss = r->o_ss;
         wss.format = r->work_format;
-        r->lfe_filter = pa_lfe_filter_new(&wss, &r->o_cm, (float)crossover_freq);
+        /* FIXME: For now just hardcode maxrewind to 3 seconds */
+        r->lfe_filter = pa_lfe_filter_new(&wss, &r->o_cm, (float)crossover_freq, b->rate * 3);
         pa_log_debug("  lfe filter activated (LR4 type), the crossover_freq = %uHz", crossover_freq);
     }