avcodec: Add a RFC 3389 comfort noise codec

This isn't too useful as a normal codec, but can be used in
voip style applications. The decoder updates the noise
generator parameters when a packet is given to it for decoding,
but if called with an empty packet, it generates more noise
according to the last parameters.

Signed-off-by: Martin Storsjö <martin@martin.st>

1 files changed, 116 insertions, 0 deletions

diff --git a/libavcodec/cngenc.c b/libavcodec/cngenc.c
new file mode 100644
index 0000000000..1e3f8f0c8d
--- /dev/null
+++ b/libavcodec/cngenc.c
@@ -0,0 +1,116 @@
+/*
+ * RFC 3389 comfort noise generator
+ * Copyright (c) 2012 Martin Storsjo
+ *
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <math.h>
+
+#include "libavutil/common.h"
+#include "avcodec.h"
+#include "internal.h"
+#include "lpc.h"
+
+typedef struct CNGContext {
+    LPCContext lpc;
+    int order;
+    int32_t *samples32;
+    double *ref_coef;
+} CNGContext;
+
+static av_cold int cng_encode_close(AVCodecContext *avctx)
+{
+    CNGContext *p = avctx->priv_data;
+    ff_lpc_end(&p->lpc);
+    av_free(p->samples32);
+    av_free(p->ref_coef);
+    return 0;
+}
+
+static av_cold int cng_encode_init(AVCodecContext *avctx)
+{
+    CNGContext *p = avctx->priv_data;
+    int ret;
+
+    if (avctx->channels != 1) {
+        av_log(avctx, AV_LOG_ERROR, "Only mono supported\n");
+        return AVERROR(EINVAL);
+    }
+
+    avctx->frame_size = 640;
+    p->order = 10;
+    if ((ret = ff_lpc_init(&p->lpc, avctx->frame_size, p->order, FF_LPC_TYPE_LEVINSON)) < 0)
+        return ret;
+    p->samples32 = av_malloc(avctx->frame_size * sizeof(*p->samples32));
+    p->ref_coef = av_malloc(p->order * sizeof(*p->ref_coef));
+    if (!p->samples32 || !p->ref_coef) {
+        cng_encode_close(avctx);
+        return AVERROR(ENOMEM);
+    }
+
+    return 0;
+}
+
+static int cng_encode_frame(AVCodecContext *avctx, AVPacket *avpkt,
+                             const AVFrame *frame, int *got_packet_ptr)
+{
+    CNGContext *p = avctx->priv_data;
+    int ret, i;
+    double energy = 0;
+    int qdbov;
+    int16_t *samples = (int16_t*) frame->data[0];
+
+    if ((ret = ff_alloc_packet(avpkt, 1 + p->order))) {
+        av_log(avctx, AV_LOG_ERROR, "Error getting output packet\n");
+        return ret;
+    }
+
+    for (i = 0; i < frame->nb_samples; i++) {
+        p->samples32[i] = samples[i];
+        energy += samples[i] * samples[i];
+    }
+    energy /= frame->nb_samples;
+    if (energy > 0) {
+        double dbov = 10 * log10(energy / 1081109975);
+        qdbov = av_clip(-floor(dbov), 0, 127);
+    } else {
+        qdbov = 127;
+    }
+    ret = ff_lpc_calc_ref_coefs(&p->lpc, p->samples32, p->order, p->ref_coef);
+    avpkt->data[0] = qdbov;
+    for (i = 0; i < p->order; i++)
+        avpkt->data[1 + i] = p->ref_coef[i] * 127 + 127;
+
+    *got_packet_ptr = 1;
+    avpkt->size = 1 + p->order;
+
+    return 0;
+}
+
+AVCodec ff_comfortnoise_encoder = {
+    .name           = "comfortnoise",
+    .type           = AVMEDIA_TYPE_AUDIO,
+    .id             = AV_CODEC_ID_COMFORT_NOISE,
+    .priv_data_size = sizeof(CNGContext),
+    .init           = cng_encode_init,
+    .encode2        = cng_encode_frame,
+    .close          = cng_encode_close,
+    .long_name      = NULL_IF_CONFIG_SMALL("RFC 3389 comfort noise generator"),
+    .sample_fmts    = (const enum AVSampleFormat[]){ AV_SAMPLE_FMT_S16,
+                                                     AV_SAMPLE_FMT_NONE },
+};