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* Interface to libgsm for gsm encoding/decoding
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* Copyright (c) 2005 Alban Bedel <albeu@free.fr>
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* Copyright (c) 2006, 2007 Michel Bardiaux <mbardiaux@mediaxim.be>
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* This file is part of FFmpeg.
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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* Interface to libgsm for gsm encoding/decoding
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// The idiosyncrasies of GSM-in-WAV are explained at http://kbs.cs.tu-berlin.de/~jutta/toast.html
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// gsm.h misses some essential constants
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#define GSM_BLOCK_SIZE 33
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#define GSM_MS_BLOCK_SIZE 65
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#define GSM_FRAME_SIZE 160
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static av_cold int libgsm_init(AVCodecContext *avctx) {
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if (avctx->channels > 1) {
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av_log(avctx, AV_LOG_ERROR, "Mono required for GSM, got %d channels\n",
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if(avctx->codec->decode){
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if(!avctx->sample_rate)
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avctx->sample_rate= 8000;
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avctx->sample_fmt = SAMPLE_FMT_S16;
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if (avctx->sample_rate != 8000) {
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av_log(avctx, AV_LOG_ERROR, "Sample rate 8000Hz required for GSM, got %dHz\n",
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if(avctx->strict_std_compliance > FF_COMPLIANCE_INOFFICIAL)
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if (avctx->bit_rate != 13000 /* Official */ &&
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avctx->bit_rate != 13200 /* Very common */ &&
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avctx->bit_rate != 0 /* Unknown; a.o. mov does not set bitrate when decoding */ ) {
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av_log(avctx, AV_LOG_ERROR, "Bitrate 13000bps required for GSM, got %dbps\n",
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if(avctx->strict_std_compliance > FF_COMPLIANCE_INOFFICIAL)
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avctx->priv_data = gsm_create();
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switch(avctx->codec_id) {
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avctx->frame_size = GSM_FRAME_SIZE;
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avctx->block_align = GSM_BLOCK_SIZE;
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case CODEC_ID_GSM_MS: {
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gsm_option(avctx->priv_data, GSM_OPT_WAV49, &one);
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avctx->frame_size = 2*GSM_FRAME_SIZE;
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avctx->block_align = GSM_MS_BLOCK_SIZE;
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avctx->coded_frame= avcodec_alloc_frame();
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avctx->coded_frame->key_frame= 1;
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static av_cold int libgsm_close(AVCodecContext *avctx) {
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av_freep(&avctx->coded_frame);
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gsm_destroy(avctx->priv_data);
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avctx->priv_data = NULL;
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static int libgsm_encode_frame(AVCodecContext *avctx,
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unsigned char *frame, int buf_size, void *data) {
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// we need a full block
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if(buf_size < avctx->block_align) return 0;
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switch(avctx->codec_id) {
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gsm_encode(avctx->priv_data,data,frame);
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case CODEC_ID_GSM_MS:
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gsm_encode(avctx->priv_data,data,frame);
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gsm_encode(avctx->priv_data,((short*)data)+GSM_FRAME_SIZE,frame+32);
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return avctx->block_align;
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AVCodec libgsm_encoder = {
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.sample_fmts = (const enum SampleFormat[]){SAMPLE_FMT_S16,SAMPLE_FMT_NONE},
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.long_name = NULL_IF_CONFIG_SMALL("libgsm GSM"),
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AVCodec libgsm_ms_encoder = {
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.sample_fmts = (const enum SampleFormat[]){SAMPLE_FMT_S16,SAMPLE_FMT_NONE},
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.long_name = NULL_IF_CONFIG_SMALL("libgsm GSM Microsoft variant"),
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static int libgsm_decode_frame(AVCodecContext *avctx,
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void *data, int *data_size,
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const uint8_t *buf = avpkt->data;
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int buf_size = avpkt->size;
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*data_size = 0; /* In case of error */
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if(buf_size < avctx->block_align) return -1;
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switch(avctx->codec_id) {
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if(gsm_decode(avctx->priv_data,buf,data)) return -1;
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*data_size = GSM_FRAME_SIZE*sizeof(int16_t);
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case CODEC_ID_GSM_MS:
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if(gsm_decode(avctx->priv_data,buf,data) ||
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gsm_decode(avctx->priv_data,buf+33,((int16_t*)data)+GSM_FRAME_SIZE)) return -1;
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*data_size = GSM_FRAME_SIZE*sizeof(int16_t)*2;
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return avctx->block_align;
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AVCodec libgsm_decoder = {
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.long_name = NULL_IF_CONFIG_SMALL("libgsm GSM"),
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AVCodec libgsm_ms_decoder = {
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.long_name = NULL_IF_CONFIG_SMALL("libgsm GSM Microsoft variant"),