libavcodec/dfpwmenc.c

   1 /*
   2  * DFPWM encoder
   3  * Copyright (c) 2022 Jack Bruienne
   4  * Copyright (c) 2012, 2016 Ben "GreaseMonkey" Russell
   5  *
   6  * This file is part of FFmpeg.
   7  *
   8  * FFmpeg is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * FFmpeg is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with FFmpeg; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 /**
  24  * @file
  25  * DFPWM1a encoder
  26  */
  27
  28 #include "libavutil/internal.h"
  29 #include "avcodec.h"
  30 #include "codec_id.h"
  31 #include "codec_internal.h"
  32 #include "encode.h"
  33
  34 typedef struct {
  35     int fq, q, s, lt;
  36 } DFPWMState;
  37
  38 // DFPWM codec from https://github.com/ChenThread/dfpwm/blob/master/1a/
  39 // Licensed in the public domain
  40
  41 // note, len denotes how many compressed bytes there are (uncompressed bytes / 8).
  42 static void au_compress(DFPWMState *state, int len, uint8_t *outbuf, const uint8_t *inbuf)
  43 {
  44     unsigned d = 0;
  45     for (int i = 0; i < len; i++) {
  46         for (int j = 0; j < 8; j++) {
  47             int nq, st, ns;
  48             // get sample
  49             int v = *(inbuf++) - 128;
  50             // set bit / target
  51             int t = (v > state->q || (v == state->q && v == 127) ? 127 : -128);
  52             d >>= 1;
  53             if(t > 0)
  54                 d |= 0x80;
  55
  56             // adjust charge
  57             nq = state->q + ((state->s * (t-state->q) + 512)>>10);
  58             if(nq == state->q && nq != t)
  59                 nq += (t == 127 ? 1 : -1);
  60             state->q = nq;
  61
  62             // adjust strength
  63             st = (t != state->lt ? 0 : 1023);
  64             ns = state->s;
  65             if(ns != st)
  66                 ns += (st != 0 ? 1 : -1);
  67             if(ns < 8) ns = 8;
  68             state->s = ns;
  69
  70             state->lt = t;
  71         }
  72
  73         // output bits
  74         *(outbuf++) = d;
  75     }
  76 }
  77
  78 static av_cold int dfpwm_enc_init(struct AVCodecContext *ctx)
  79 {
  80     DFPWMState *state = ctx->priv_data;
  81
  82     state->fq = 0;
  83     state->q = 0;
  84     state->s = 0;
  85     state->lt = -128;
  86
  87     ctx->bits_per_coded_sample = 1;
  88
  89     return 0;
  90 }
  91
  92 static int dfpwm_enc_frame(struct AVCodecContext *ctx, struct AVPacket *packet,
  93     const struct AVFrame *frame, int *got_packet)
  94 {
  95     DFPWMState *state = ctx->priv_data;
  96     int size = frame->nb_samples * frame->ch_layout.nb_channels / 8 + (frame->nb_samples % 8 > 0 ? 1 : 0);
  97     int ret = ff_get_encode_buffer(ctx, packet, size, 0);
  98
  99     if (ret) {
 100         *got_packet = 0;
 101         return ret;
 102     }
 103
 104     au_compress(state, size, packet->data, frame->data[0]);
 105
 106     *got_packet = 1;
 107     return 0;
 108 }
 109
 110 const FFCodec ff_dfpwm_encoder = {
 111     .p.name          = "dfpwm",
 112     CODEC_LONG_NAME("DFPWM1a audio"),
 113     .p.type          = AVMEDIA_TYPE_AUDIO,
 114     .p.id            = AV_CODEC_ID_DFPWM,
 115     .priv_data_size  = sizeof(DFPWMState),
 116     .init            = dfpwm_enc_init,
 117     FF_CODEC_ENCODE_CB(dfpwm_enc_frame),
 118     .p.sample_fmts   = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_U8, AV_SAMPLE_FMT_NONE},
 119     .p.capabilities  = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_VARIABLE_FRAME_SIZE |
 120                        AV_CODEC_CAP_ENCODER_REORDERED_OPAQUE,
 121 };