libavdevice/alsa-audio-dec.c

   1 /*
   2  * ALSA input and output
   3  * Copyright (c) 2007 Luca Abeni ( lucabe72 email it )
   4  * Copyright (c) 2007 Benoit Fouet ( benoit fouet free fr )
   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 libavdevice/alsa-audio-dec.c
  25  * ALSA input and output: input
  26  * @author Luca Abeni ( lucabe72 email it )
  27  * @author Benoit Fouet ( benoit fouet free fr )
  28  * @author Nicolas George ( nicolas george normalesup org )
  29  *
  30  * This avdevice decoder allows to capture audio from an ALSA (Advanced
  31  * Linux Sound Architecture) device.
  32  *
  33  * The filename parameter is the name of an ALSA PCM device capable of
  34  * capture, for example "default" or "plughw:1"; see the ALSA documentation
  35  * for naming conventions. The empty string is equivalent to "default".
  36  *
  37  * The capture period is set to the lower value available for the device,
  38  * which gives a low latency suitable for real-time capture.
  39  *
  40  * The PTS are an Unix time in microsecond.
  41  *
  42  * Due to a bug in the ALSA library
  43  * (https://bugtrack.alsa-project.org/alsa-bug/view.php?id=4308), this
  44  * decoder does not work with certain ALSA plugins, especially the dsnoop
  45  * plugin.
  46  */
  47
  48 #include "libavformat/avformat.h"
  49 #include <alsa/asoundlib.h>
  50
  51 #include "alsa-audio.h"
  52
  53 av_cold static int audio_read_header(AVFormatContext *s1,
  54                                      AVFormatParameters *ap)
  55 {
  56     AlsaData *s = s1->priv_data;
  57     AVStream *st;
  58     int ret;
  59     unsigned int sample_rate;
  60     enum CodecID codec_id;
  61     snd_pcm_sw_params_t *sw_params;
  62
  63     if (ap->sample_rate <= 0) {
  64         av_log(s1, AV_LOG_ERROR, "Bad sample rate %d\n", ap->sample_rate);
  65
  66         return AVERROR(EIO);
  67     }
  68
  69     if (ap->channels <= 0) {
  70         av_log(s1, AV_LOG_ERROR, "Bad channels number %d\n", ap->channels);
  71
  72         return AVERROR(EIO);
  73     }
  74
  75     st = av_new_stream(s1, 0);
  76     if (!st) {
  77         av_log(s1, AV_LOG_ERROR, "Cannot add stream\n");
  78
  79         return AVERROR(ENOMEM);
  80     }
  81     sample_rate = ap->sample_rate;
  82     codec_id    = ap->audio_codec_id;
  83
  84     ret = ff_alsa_open(s1, SND_PCM_STREAM_CAPTURE, &sample_rate, ap->channels,
  85         &codec_id);
  86     if (ret < 0) {
  87         return AVERROR(EIO);
  88     }
  89
  90     if (snd_pcm_type(s->h) != SND_PCM_TYPE_HW)
  91         av_log(s1, AV_LOG_WARNING,
  92                "capture with some ALSA plugins, especially dsnoop, "
  93                "may hang.\n");
  94
  95     ret = snd_pcm_sw_params_malloc(&sw_params);
  96     if (ret < 0) {
  97         av_log(s1, AV_LOG_ERROR, "cannot allocate software parameters structure (%s)\n",
  98                snd_strerror(ret));
  99         goto fail;
 100     }
 101
 102     snd_pcm_sw_params_current(s->h, sw_params);
 103     snd_pcm_sw_params_set_tstamp_mode(s->h, sw_params, SND_PCM_TSTAMP_ENABLE);
 104
 105     ret = snd_pcm_sw_params(s->h, sw_params);
 106     snd_pcm_sw_params_free(sw_params);
 107     if (ret < 0) {
 108         av_log(s1, AV_LOG_ERROR, "cannot install ALSA software parameters (%s)\n",
 109                snd_strerror(ret));
 110         goto fail;
 111     }
 112
 113     /* take real parameters */
 114     st->codec->codec_type  = CODEC_TYPE_AUDIO;
 115     st->codec->codec_id    = codec_id;
 116     st->codec->sample_rate = sample_rate;
 117     st->codec->channels    = ap->channels;
 118     av_set_pts_info(st, 64, 1, 1000000);  /* 64 bits pts in us */
 119
 120     return 0;
 121
 122 fail:
 123     snd_pcm_close(s->h);
 124     return AVERROR(EIO);
 125 }
 126
 127 static int audio_read_packet(AVFormatContext *s1, AVPacket *pkt)
 128 {
 129     AlsaData *s  = s1->priv_data;
 130     AVStream *st = s1->streams[0];
 131     int res;
 132     snd_htimestamp_t timestamp;
 133     snd_pcm_uframes_t ts_delay;
 134
 135     if (av_new_packet(pkt, s->period_size) < 0) {
 136         return AVERROR(EIO);
 137     }
 138
 139     while ((res = snd_pcm_readi(s->h, pkt->data, pkt->size / s->frame_size)) < 0) {
 140         if (res == -EAGAIN) {
 141             av_free_packet(pkt);
 142
 143             return AVERROR(EAGAIN);
 144         }
 145         if (ff_alsa_xrun_recover(s1, res) < 0) {
 146             av_log(s1, AV_LOG_ERROR, "ALSA read error: %s\n",
 147                    snd_strerror(res));
 148             av_free_packet(pkt);
 149
 150             return AVERROR(EIO);
 151         }
 152     }
 153
 154     snd_pcm_htimestamp(s->h, &ts_delay, &timestamp);
 155     ts_delay += res;
 156     pkt->pts = timestamp.tv_sec * 1000000LL
 157                + (timestamp.tv_nsec * st->codec->sample_rate
 158                   - ts_delay * 1000000000LL + st->codec->sample_rate * 500LL)
 159                / (st->codec->sample_rate * 1000LL);
 160
 161     pkt->size = res * s->frame_size;
 162
 163     return 0;
 164 }
 165
 166 AVInputFormat alsa_demuxer = {
 167     "alsa",
 168     NULL_IF_CONFIG_SMALL("ALSA audio input"),
 169     sizeof(AlsaData),
 170     NULL,
 171     audio_read_header,
 172     audio_read_packet,
 173     ff_alsa_close,
 174     .flags = AVFMT_NOFILE,
 175 };