FFmpeg简单使用：音频解码 ---- 提取pcm
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FFmpeg简单使用：过滤器 ---- h264_mp4toannexb
FFmpeg简单使用：解封装h264 ---- 提取SPS PPS
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基本流程：
编码：
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <libavutil/frame.h> #include <libavutil/mem.h> #include <libavcodec/avcodec.h> #define AUDIO_INBUF_SIZE 20480 #define AUDIO_REFILL_THRESH 4096 static char err_buf[128] = {0}; static char* av_get_err(int errnum) { av_strerror(errnum, err_buf, 128); return err_buf; } static void print_sample_format(const AVFrame *frame) { printf("ar-samplerate: %uHz\n", frame->sample_rate); printf("ac-channel: %u\n", frame->channels); printf("f-format: %u\n", frame->format);// 格式需要注意，实际存储到本地文件时已经改成交错模式 } static void decode(AVCodecContext *dec_ctx, AVPacket *pkt, AVFrame *frame, FILE *outfile) { int i, ch; int ret, data_size; /* send the packet with the compressed data to the decoder */ ret = avcodec_send_packet(dec_ctx, pkt); if(ret == AVERROR(EAGAIN)) { fprintf(stderr, "Receive_frame and send_packet both returned EAGAIN, which is an API violation.\n"); } else if (ret < 0) { fprintf(stderr, "Error submitting the packet to the decoder, err:%s, pkt_size:%d\n", av_get_err(ret), pkt->size); // exit(1); return; } /* read all the output frames (infile general there may be any number of them */ while (ret >= 0) { // 对于frame, avcodec_receive_frame内部每次都先调用 ret = avcodec_receive_frame(dec_ctx, frame); if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) return; else if (ret < 0) { fprintf(stderr, "Error during decoding\n"); exit(1); } data_size = av_get_bytes_per_sample(dec_ctx->sample_fmt); if (data_size < 0) { /* This should not occur, checking just for paranoia */ fprintf(stderr, "Failed to calculate data size\n"); exit(1); } static int s_print_format = 0; if(s_print_format == 0) { s_print_format = 1; print_sample_format(frame); } /** P表示Planar（平面），其数据格式排列方式为 : LLLLLLRRRRRRLLLLLLRRRRRRLLLLLLRRRRRRL...（每个LLLLLLRRRRRR为一个音频帧） 而不带P的数据格式（即交错排列）排列方式为： LRLRLRLRLRLRLRLRLRLRLRLRLRLRLRLRLRLRL...（每个LR为一个音频样本） 播放范例： ffplay -ar 48000 -ac 2 -f f32le believe.pcm */ for (i = 0; i < frame->nb_samples; i++) { for (ch = 0; ch < dec_ctx->channels; ch++) // 交错的方式写入, 大部分float的格式输出 fwrite(frame->data[ch] + data_size*i, 1, data_size, outfile); } } } // 播放范例： ffplay -ar 48000 -ac 2 -f f32le believe.pcm int main(int argc, char **argv) { const char *outfilename; const char *filename; const AVCodec *codec; AVCodecContext *codec_ctx= NULL; AVCodecParserContext *parser = NULL; int len = 0; int ret = 0; FILE *infile = NULL; FILE *outfile = NULL; uint8_t inbuf[AUDIO_INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE]; uint8_t *data = NULL; size_t data_size = 0; AVPacket *pkt = NULL; AVFrame *decoded_frame = NULL; if (argc <= 2) { fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]); exit(0); } filename = argv[1]; outfilename = argv[2]; pkt = av_packet_alloc(); enum AVCodecID audio_codec_id = AV_CODEC_ID_AAC; if(strstr(filename, "aac") != NULL) { audio_codec_id = AV_CODEC_ID_AAC; } else if(strstr(filename, "mp3") != NULL) { audio_codec_id = AV_CODEC_ID_MP3; } else { printf("default codec id:%d\n", audio_codec_id); } // 查找解码器 codec = avcodec_find_decoder(audio_codec_id); // AV_CODEC_ID_AAC if (!codec) { fprintf(stderr, "Codec not found\n"); exit(1); } // 获取裸流的解析器 AVCodecParserContext(数据) + AVCodecParser(方法) parser = av_parser_init(audio_codec_id); if (!parser) { fprintf(stderr, "Parser not found\n"); exit(1); } // 分配codec上下文 codec_ctx = avcodec_alloc_context3(codec); if (!codec_ctx) { fprintf(stderr, "Could not allocate audio codec context\n"); exit(1); } // 将解码器和解码器上下文进行关联 if (avcodec_open2(codec_ctx, codec, NULL) < 0) { fprintf(stderr, "Could not open codec\n"); exit(1); } // 打开输入文件 infile = fopen(filename, "rb"); if (!infile) { fprintf(stderr, "Could not open %s\n", filename); exit(1); } // 打开输出文件 outfile = fopen(outfilename, "wb"); if (!outfile) { av_free(codec_ctx); exit(1); } // 读取文件进行解码 data = inbuf; data_size = fread(inbuf, 1, AUDIO_INBUF_SIZE, infile); while (data_size > 0) { if (!decoded_frame) { if (!(decoded_frame = av_frame_alloc())) { fprintf(stderr, "Could not allocate audio frame\n"); exit(1); } } ret = av_parser_parse2(parser, codec_ctx, &pkt->data, &pkt->size, data, data_size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0); if (ret < 0) { fprintf(stderr, "Error while parsing\n"); exit(1); } data += ret; // 跳过已经解析的数据 data_size -= ret; // 对应的缓存大小也做相应减小 if (pkt->size) decode(codec_ctx, pkt, decoded_frame, outfile); if (data_size < AUDIO_REFILL_THRESH) // 如果数据少了则再次读取 { memmove(inbuf, data, data_size); // 把之前剩的数据拷贝到buffer的起始位置 data = inbuf; // 读取数据 长度: AUDIO_INBUF_SIZE - data_size len = fread(data + data_size, 1, AUDIO_INBUF_SIZE - data_size, infile); if (len > 0) data_size += len; } } /* 冲刷解码器 */ pkt->data = NULL; // 让其进入drain mode pkt->size = 0; decode(codec_ctx, pkt, decoded_frame, outfile); fclose(outfile); fclose(infile); avcodec_free_context(&codec_ctx); av_parser_close(parser); av_frame_free(&decoded_frame); av_packet_free(&pkt); printf("main finish, please enter Enter and exit\n"); return 0; }
