云南网站建设专业品牌,自动生成设计logo图标,成都公司注册地址有什么要求,软件开发好学吗?对于从音频流buffer中解码的场景中#xff0c;我们需要实现自己的io context 去从buffer中解码#xff0c;参考ffmepg官方实例#xff1a;doc/examples/avio_reading.c
关于是否要实现avio context中的seek函数#xff0c;需要看需要解码什么格式#xff0c;大部分格式不… 对于从音频流buffer中解码的场景中我们需要实现自己的io context 去从buffer中解码参考ffmepg官方实例doc/examples/avio_reading.c
关于是否要实现avio context中的seek函数需要看需要解码什么格式大部分格式不需要seek,但是有些格式需要比如apple开发的ALAC格式这个格式的音频有的时候它的头文件moov信息是在文件的结尾这就很坑一般都是在开头所以在获取音频的时候需要先seek到文件的结尾获取moov的信息然后再seek回来继续解析格式并解码。
关于moov格式的坑【开发笔记】终于我们解决了iOS播放器的一个Bug... - 哔哩哔哩
如果你不想实现seek有没有办法直接把音频文件的moov信息从结尾提到开头呢也是有的
ffmpeg -i ./old.mp4 -movflags faststart -c copy new.mp4
通过这个命令转换后再去解码文件信息就在开头就可以不用seek了。
可以通过以下命令去查看头文件信息
ffprobe -v trace filename
直接贴代码
#include libavcodec/avcodec.h
#include libavformat/avformat.h
#include libavformat/avio.h
#include libavutil/file.h
#include libavutil/frame.h
#include libavutil/mem.h
#include stdio.h
#include stdlib.h
#include string.h#define BUF_SIZE 20480FILE *in_file NULL;struct buffer_data {uint8_t *ptr;uint8_t *ori_ptr; // for seek file streamsize_t size; /// size left in the buffersize_t file_size; /// size of the file to decode
};static char *av_get_err(int errnum) {static char err_buf[128] {0};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
}
/*
int read_size;static int read_packet(void *opaque, uint8_t *buf, int buf_size) {// FILE *in_file (FILE *)opaque;read_size fread(buf, 1, buf_size, in_file);printf(read_packet read_size:%d, buf_size:%d\n, read_size, buf_size);if (read_size 0) {return AVERROR_EOF; // 数据读取完毕}return read_size;
}
*/
static int read_packet(void *opaque, uint8_t *buf, int buf_size) {struct buffer_data *bd (struct buffer_data *)opaque;buf_size FFMIN(buf_size, bd-size);if (!buf_size) return AVERROR_EOF;// printf(ptr:%p size:%zu buf_size: %d\n, bd-ptr, bd-size, buf_size);/* copy internal buffer data to buf */memcpy(buf, bd-ptr, buf_size);bd-ptr buf_size;bd-size - buf_size;return buf_size;
}// for some format like ALAC (apple format) , which moov partten is located at
// the end of file so we need to implement seek function during demux to seek to
// the end of file for paring the moov info and then seek back to the front
static int64_t seek_packet(void *opaque, int64_t offset, int whence) {// FILE *in_file (FILE *)opaque;struct buffer_data *bd (struct buffer_data *)opaque;int64_t ret -1;printf(whence%d , offset%lld \n, whence, offset);switch (whence) {case AVSEEK_SIZE:printf(AVSEEK_SIZE \n);ret bd-file_size;break;case SEEK_SET:printf(SEEK_SET \n);bd-ptr bd-ori_ptr offset;bd-size bd-file_size - offset;ret bd-ptr;break;case SEEK_CUR:printf(SEEK_cur \n);break;case SEEK_END:printf(SEEK_end \n);break;}return ret;
}static void decode(AVCodecContext *dec_ctx, AVPacket *packet, AVFrame *frame,FILE *outfile) {int ret 0;ret avcodec_send_packet(dec_ctx, packet);if (ret AVERROR(EAGAIN)) {printf(Receive_frame and send_packet both returned EAGAIN, which is an API violation.\n);} else if (ret 0) {printf(Error submitting the packet to the decoder, err:%s\n,av_get_err(ret));return;}while (ret 0) {ret avcodec_receive_frame(dec_ctx, frame);if (ret AVERROR(EAGAIN) || ret AVERROR_EOF) {return;} else if (ret 0) {printf(Error during decoding\n);exit(1);}if (!packet) {printf(get flush frame\n);}int out_sample_bytes av_get_bytes_per_sample(dec_ctx-sample_fmt);int out_sample_is_plannar av_sample_fmt_is_planar(dec_ctx-sample_fmt);// printf(debug %d is out_sample_is_plannar : %d \n, __LINE__,// out_sample_is_plannar);// print_sample_format(frame);if (out_sample_bytes 0) {/* This should not occur, checking just for paranoia */fprintf(stderr, Failed to calculate data size\n);exit(1);}// printf(debug %d out_sample_bytes: %d samples: %d ch:%d\n, __LINE__,// out_sample_bytes, frame-nb_samples,// dec_ctx-ch_layout.nb_channels);if (out_sample_is_plannar) { // plannar frames/**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并不是每一种都是这样的格式*/// 这里的写法不是通用通用要调用重采样的函数去实现// 这里只是针对解码出来是planar格式的转换for (int i 0; i frame-nb_samples; i) {for (int ch 0; ch frame-channels; ch) {// for(int ch 0; ch 1; ch) {fwrite(frame-data[ch] out_sample_bytes * i, 1, out_sample_bytes,outfile);}}} else // packed framefwrite(frame-data[0],frame-nb_samples * out_sample_bytes * frame-channels, 1,outfile);}
}int main(int argc, char **argv) {if (argc ! 3) {printf(usage: %s intput file out file\n, argv[0]);return -1;}av_log_set_level(AV_LOG_TRACE);const char *in_file_name argv[1];const char *out_file_name argv[2];// FILE *in_file NULL;FILE *out_file NULL;// 1. 打开参数文件in_file fopen(in_file_name, rb);if (!in_file) {printf(open file %s failed\n, in_file_name);return -1;}out_file fopen(out_file_name, wb);if (!out_file) {printf(open file %s failed\n, out_file_name);return -1;}struct buffer_data bd {0};uint8_t *buffer NULL;size_t buffer_size;int ret av_file_map(in_file_name, buffer, buffer_size, 0, NULL);printf(file size: %d\n, buffer_size);bd.ptr buffer;bd.ori_ptr buffer;bd.file_size buffer_size;bd.size buffer_size;// AVInputFormat* in_fmt av_find_input_format(flac);// 2自定义 iouint8_t *io_buffer av_malloc(BUF_SIZE);// AVIOContext *avio_ctx avio_alloc_context(io_buffer, BUF_SIZE, 0, (void// *)in_file,AVIOContext *avio_ctx avio_alloc_context(io_buffer, BUF_SIZE, 0, bd,read_packet, NULL, seek_packet);// avio_alloc_context(io_buffer, BUF_SIZE, 0, bd, read_packet, NULL, NULL);AVFormatContext *format_ctx avformat_alloc_context();format_ctx-pb avio_ctx;format_ctx-flags AVFMT_FLAG_CUSTOM_IO;// int ret avformat_open_input(format_ctx, NULL, in_fmt, NULL);// 从输入源读取封装格式文件头ret avformat_open_input(format_ctx, NULL, NULL, NULL);if (ret 0) {printf(avformat_open_input failed:%s\n, av_err2str(ret));return -1;}// 从输入源读取一段数据尝试解码以获取流信息if ((ret avformat_find_stream_info(format_ctx, NULL)) 0) {av_log(NULL, AV_LOG_ERROR, Cannot find stream information\n);return ret;}av_dump_format(format_ctx, 0, NULL, 0);int audioStreamIndex av_find_best_stream(format_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);AVStream *st format_ctx-streams[audioStreamIndex];// 编码器查找// AVCodec *codec avcodec_find_decoder(AV_CODEC_ID_ALAC);// set codec id from famat paramsAVCodec *codec avcodec_find_decoder(st-codecpar-codec_id);if (!codec) {printf(avcodec_find_decoder failed\n);return -1;}AVCodecContext *codec_ctx avcodec_alloc_context3(codec);if (!codec_ctx) {printf(avcodec_alloc_context3 failed\n);return -1;}// copy params from format to codecret avcodec_parameters_to_context(codec_ctx, format_ctx-streams[audioStreamIndex]-codecpar);if (ret 0) {printf(Failed to copy in_stream codecpar to codec context\n);}ret avcodec_open2(codec_ctx, codec, NULL);if (ret 0) {printf(avcodec_open2 failed:%s\n, av_err2str(ret));return -1;}printf(%d debug codec_ctx-sample_rate: %d\n, __LINE__,codec_ctx-sample_rate);AVPacket *packet av_packet_alloc();AVFrame *frame av_frame_alloc();while (1) {ret av_read_frame(format_ctx, packet);if (ret 0) {printf(av_read_frame failed:%s\n, av_err2str(ret));break;}decode(codec_ctx, packet, frame, out_file);}printf(read file finish\n);decode(codec_ctx, NULL, frame, out_file);fclose(in_file);fclose(out_file);av_frame_free(frame);av_packet_free(packet);avformat_close_input(format_ctx);avcodec_free_context(codec_ctx);printf(main finish\n);return 0;
}m4a moov 格式解析MP4格式解析---M4A是MP4中的音频部分_m4a格式解析_一个专研技术的小蜜蜂的博客-CSDN博客mp4文件格式解析 - 知乎参考ffmpeg 利用AVIOContext自定义IO 输出结果写buffer - 知乎
Creating Custom FFmpeg IO-Context - CodeProject
ffmpeg AVIOContext 自定义 IO 及 seek
