ast->codec->codec_type = AVMEDIA_TYPE_AUDIO;
ast->codec->codec_id = CODEC_ID_PCM_U8;
ast->codec->channels = 1;
ast->codec->bits_per_coded_sample = 8;
ast->codec->bit_rate = ast->codec->sample_rate * 8;
ast->codec->codec_type = AVMEDIA_TYPE_AUDIO;
ast->codec->codec_id = CODEC_ID_PCM_U8;
ast->codec->channels = 1;
ast->codec->bits_per_coded_sample = 8;
ast->codec->bit_rate = ast->codec->sample_rate * 8;