ffmpeg -formats 
ffmpeg -sample_fmts
ffmpeg -i ../english14.mp3 -ar 44100 -ac 2 -sample_fmt s16 -f wav english14.wav
ffmpeg -i ../english14.mp3 -ar 44100 -ac 2 -sample_fmt s16 -f s16le english14.pcm其中针对PCM个数的数据aplay正确的播放格式为：
aplay -r 48000 -c 2 english14.pcm 
下面都是错误的格式，声音不能正常识别
aplay -c 2 english14.pcm 
aplay -r 48000 english14.pcm 
aplay english14.pcm/home/suiyuan626/share/alsa-utils-1.2.6/aplay/aplay -v -t raw -f S16_LE -r 48000 -c 2 english14.pcm此处的aplay来自alsa-utils-1.2.6中源码编译
suiyuan626@ubuntu:~/share/ffmpeg/ffmpeg/doc/examples/data$ /home/suiyuan626/share/alsa-utils-1.2.6/aplay/aplay -v -f S16_LE -r 48000 -c 2 english14.pcm 
Playing raw data 'english14.pcm' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
ALSA <-> PulseAudio PCM I/O Plugin
Its setup is:stream       : PLAYBACKaccess       : RW_INTERLEAVEDformat       : S16_LEsubformat    : STDchannels     : 2rate         : 48000exact rate   : 48000 (48000/1)msbits       : 16buffer_size  : 24000period_size  : 6000period_time  : 125000tstamp_mode  : NONEtstamp_type  : GETTIMEOFDAYperiod_step  : 1avail_min    : 6000period_event : 0start_threshold  : 24000stop_threshold   : 24000silence_threshold: 0silence_size : 0boundary     : 6755399441055744000
^CAborted by signal Interrupt...
上面的命令中使用 -f -r -c 参数参数 -f ,其主要配置的是 根据用户给定的参数格式找出PCM.h中定义的采样个事，采样率和通道数case 'f':force_sample_format = 1;if (strcasecmp(optarg, "cd") == 0 || strcasecmp(optarg, "cdr") == 0) {if (strcasecmp(optarg, "cdr") == 0)rhwparams.format = SND_PCM_FORMAT_S16_BE;elserhwparams.format = file_type == FORMAT_AU ? SND_PCM_FORMAT_S16_BE : SND_PCM_FORMAT_S16_LE;rhwparams.rate = 44100;rhwparams.channels = 2;} else if (strcasecmp(optarg, "dat") == 0) {rhwparams.format = file_type == FORMAT_AU ? SND_PCM_FORMAT_S16_BE : SND_PCM_FORMAT_S16_LE;rhwparams.rate = 48000;rhwparams.channels = 2;} else {rhwparams.format = snd_pcm_format_value(optarg);if (rhwparams.format == SND_PCM_FORMAT_UNKNOWN) {error(_("wrong extended format '%s'"), optarg);prg_exit(EXIT_FAILURE);}}break;case 'r':tmp = parse_long(optarg, &err);if (err < 0) {error(_("invalid rate argument '%s'"), optarg);return 1;}if (tmp < 1000)tmp *= 1000;rhwparams.rate = tmp;if (tmp < 2000 || tmp > 768000) {error(_("bad speed value %i"), tmp);return 1;}breakcase 'c':rhwparams.channels = parse_long(optarg, &err);if (err < 0) {error(_("invalid channels argument '%s'"), optarg);return 1;}if (rhwparams.channels < 1 || rhwparams.channels > 256) {error(_("value %i for channels is invalid"), rhwparams.channels);return 1;}break;使用aplay要么record，要么播放文件，从stream的定义中可以知道
/** PCM stream (direction) */
typedef enum _snd_pcm_stream {/** Playback stream */SND_PCM_STREAM_PLAYBACK = 0,/** Capture stream */SND_PCM_STREAM_CAPTURE,SND_PCM_STREAM_LAST = SND_PCM_STREAM_CAPTURE
} snd_pcm_stream_t;static void header(int rtype, char *name)
{if (!quiet_mode) {if (! name)name = (stream == SND_PCM_STREAM_PLAYBACK) ? "stdout" : "stdin";fprintf(stderr, "%s %s '%s' : ",(stream == SND_PCM_STREAM_PLAYBACK) ? _("Playing") : _("Recording"),gettext(fmt_rec_table[rtype].what),name);fprintf(stderr, "%s, ", snd_pcm_format_description(hwparams.format));fprintf(stderr, _("Rate %d Hz, "), hwparams.rate);if (hwparams.channels == 1)fprintf(stderr, _("Mono"));else if (hwparams.channels == 2)fprintf(stderr, _("Stereo"));elsefprintf(stderr, _("Channels %i"), hwparams.channels);fprintf(stderr, "\n");}
}有没有设置-I参数，故执行playback()函数进行播放，同时我们可以添加参数 -t 来执行播放文件类型case 't':if (strcasecmp(optarg, "raw") == 0)file_type = FORMAT_RAW;else if (strcasecmp(optarg, "voc") == 0)file_type = FORMAT_VOC;else if (strcasecmp(optarg, "wav") == 0)file_type = FORMAT_WAVE;else if (strcasecmp(optarg, "au") == 0 || strcasecmp(optarg, "sparc") == 0)file_type = FORMAT_AU;else {error(_("unrecognized file format %s"), optarg);return 1;}break;static void playback(char *name)
{int loaded = 0;pbrec_count = LLONG_MAX;fdcount = 0;if (!name || !strcmp(name, "-")) {fd = fileno(stdin);name = "stdin";} else {init_stdin();if ((fd = open(name, O_RDONLY, 0)) == -1) {perror(name);prg_exit(EXIT_FAILURE);}}printf("name:%s,file_type:%d\n",name,file_type);switch(file_type) {case FORMAT_AU:playback_au(name, &loaded);break;case FORMAT_VOC:playback_voc(name, &loaded);break;case FORMAT_WAVE:playback_wave(name, &loaded);break;case FORMAT_RAW:playback_raw(name, &loaded);break;default:/* parse the file header */printf("file_type:%d\n",file_type);if (playback_au(name, &loaded) < 0 &&playback_voc(name, &loaded) < 0 &&playback_wave(name, &loaded) < 0)playback_raw(name, &loaded); /* should be raw data */break;}if (fd != fileno(stdin))close(fd);
}
其四个函数的额处理差异，主要是处理了文件头，比如播放的为PCM或者WAV格式的文件，而给定的参数-t au/voc 将不会进行播放。