xref: /third_party/ffmpeg/libavformat/gsmdec.c (revision cabdff1a) 
1/*
2 * RAW GSM demuxer
3 * Copyright (c) 2011 Justin Ruggles
4 *
5 * This file is part of FFmpeg.
6 *
7 * FFmpeg is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * FFmpeg is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with FFmpeg; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22#include "libavutil/channel_layout.h"
23#include "libavutil/mathematics.h"
24#include "libavutil/opt.h"
25#include "avformat.h"
26#include "internal.h"
27
28#define GSM_BLOCK_SIZE    33
29#define GSM_BLOCK_SAMPLES 160
30#define GSM_SAMPLE_RATE   8000
31
32typedef struct GSMDemuxerContext {
33    AVClass *class;
34    int sample_rate;
35} GSMDemuxerContext;
36
37static int gsm_probe(const AVProbeData *p)
38{
39    int valid = 0, invalid = 0;
40    uint8_t *b = p->buf;
41    while (b < p->buf + p->buf_size - 32) {
42        if ((*b & 0xf0) == 0xd0) {
43            valid++;
44        } else {
45            invalid++;
46        }
47        b += 33;
48    }
49    if (valid >> 5 > invalid)
50        return AVPROBE_SCORE_EXTENSION + 1;
51    return 0;
52}
53
54static int gsm_read_packet(AVFormatContext *s, AVPacket *pkt)
55{
56    int ret, size;
57
58    size = GSM_BLOCK_SIZE;
59
60    pkt->pos = avio_tell(s->pb);
61    pkt->stream_index = 0;
62
63    ret = av_get_packet(s->pb, pkt, size);
64    if (ret < GSM_BLOCK_SIZE) {
65        return ret < 0 ? ret : AVERROR(EIO);
66    }
67    pkt->duration = 1;
68    pkt->pts      = pkt->pos / GSM_BLOCK_SIZE;
69
70    return 0;
71}
72
73static int gsm_read_header(AVFormatContext *s)
74{
75    GSMDemuxerContext *c = s->priv_data;
76    AVStream *st = avformat_new_stream(s, NULL);
77    if (!st)
78        return AVERROR(ENOMEM);
79
80    st->codecpar->codec_type  = AVMEDIA_TYPE_AUDIO;
81    st->codecpar->codec_id    = s->iformat->raw_codec_id;
82    st->codecpar->ch_layout   = (AVChannelLayout)AV_CHANNEL_LAYOUT_MONO;
83    st->codecpar->sample_rate = c->sample_rate;
84    st->codecpar->bit_rate    = GSM_BLOCK_SIZE * 8 * c->sample_rate / GSM_BLOCK_SAMPLES;
85
86    avpriv_set_pts_info(st, 64, GSM_BLOCK_SAMPLES, GSM_SAMPLE_RATE);
87
88    return 0;
89}
90
91static const AVOption options[] = {
92    { "sample_rate", "", offsetof(GSMDemuxerContext, sample_rate),
93       AV_OPT_TYPE_INT, {.i64 = GSM_SAMPLE_RATE}, 1, INT_MAX / GSM_BLOCK_SIZE,
94       AV_OPT_FLAG_DECODING_PARAM },
95    { NULL },
96};
97
98static const AVClass gsm_class = {
99    .class_name = "gsm demuxer",
100    .item_name  = av_default_item_name,
101    .option     = options,
102    .version    = LIBAVUTIL_VERSION_INT,
103};
104
105const AVInputFormat ff_gsm_demuxer = {
106    .name           = "gsm",
107    .long_name      = NULL_IF_CONFIG_SMALL("raw GSM"),
108    .priv_data_size = sizeof(GSMDemuxerContext),
109    .read_probe     = gsm_probe,
110    .read_header    = gsm_read_header,
111    .read_packet    = gsm_read_packet,
112    .flags          = AVFMT_GENERIC_INDEX,
113    .extensions     = "gsm",
114    .raw_codec_id   = AV_CODEC_ID_GSM,
115    .priv_class     = &gsm_class,
116};
117