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/*
* DFPWM encoder
* Copyright (c) 2022 Jack Bruienne
* Copyright (c) 2012, 2016 Ben "GreaseMonkey" Russell
*
* This file is part of FFmpeg.
*
* FFmpeg 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.
*
* FFmpeg 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 FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file
* DFPWM1a encoder
*/
#include "libavutil/internal.h"
#include "avcodec.h"
#include "codec_id.h"
#include "encode.h"
#include "internal.h"
typedef struct {
int fq, q, s, lt;
} DFPWMState;
// DFPWM codec from https://github.com/ChenThread/dfpwm/blob/master/1a/
// Licensed in the public domain
// note, len denotes how many compressed bytes there are (uncompressed bytes / 8).
static void au_compress(DFPWMState *state, int len, uint8_t *outbuf, uint8_t *inbuf)
{
unsigned d = 0;
for (int i = 0; i < len; i++) {
for (int j = 0; j < 8; j++) {
int nq, st, ns;
// get sample
int v = *(inbuf++) - 128;
// set bit / target
int t = (v > state->q || (v == state->q && v == 127) ? 127 : -128);
d >>= 1;
if(t > 0)
d |= 0x80;
// adjust charge
nq = state->q + ((state->s * (t-state->q) + 512)>>10);
if(nq == state->q && nq != t)
nq += (t == 127 ? 1 : -1);
state->q = nq;
// adjust strength
st = (t != state->lt ? 0 : 1023);
ns = state->s;
if(ns != st)
ns += (st != 0 ? 1 : -1);
if(ns < 8) ns = 8;
state->s = ns;
state->lt = t;
}
// output bits
*(outbuf++) = d;
}
}
static av_cold int dfpwm_enc_init(struct AVCodecContext *ctx)
{
DFPWMState *state = ctx->priv_data;
state->fq = 0;
state->q = 0;
state->s = 0;
state->lt = -128;
ctx->bits_per_coded_sample = 1;
return 0;
}
static int dfpwm_enc_frame(struct AVCodecContext *ctx, struct AVPacket *packet,
const struct AVFrame *frame, int *got_packet)
{
DFPWMState *state = ctx->priv_data;
int size = frame->nb_samples * frame->channels / 8 + (frame->nb_samples % 8 > 0 ? 1 : 0);
int ret = ff_get_encode_buffer(ctx, packet, size, 0);
if (ret) {
*got_packet = 0;
return ret;
}
au_compress(state, size, packet->data, frame->data[0]);
*got_packet = 1;
return 0;
}
const AVCodec ff_dfpwm_encoder = {
.name = "dfpwm",
.long_name = NULL_IF_CONFIG_SMALL("DFPWM1a audio"),
.type = AVMEDIA_TYPE_AUDIO,
.id = AV_CODEC_ID_DFPWM,
.priv_data_size = sizeof(DFPWMState),
.init = dfpwm_enc_init,
.encode2 = dfpwm_enc_frame,
.sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_U8, AV_SAMPLE_FMT_NONE},
.capabilities = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_VARIABLE_FRAME_SIZE,
.caps_internal = FF_CODEC_CAP_INIT_THREADSAFE,
};
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