FFmpeg(五) 重采样相关函数理解
一、重采样流程
重采样(解码音频数据之后格式不可以直接播放，需要重采样，类似图像的像素转换)
1.分配上下文
2.设置参数（分为（前几个是）输出格式和（后几个）输入格式，两个相对应的） 可以通过改变样本率来改变音频的播放速度，但是会失帧。
3.初始化
4.开始转换
二、相关函数说明
1、 SwrContext *actx = swr_alloc(); //进行分配和初始化
2、 actx = swr_alloc_set_opts(actx,
av_get_default_channel_layout(2), //输出标准（左右声道)
AV_SAMPLE_FMT_S16, //样本格式：float 、s16、s24
ac->sample_rate,//样本率，一般使用原始的
av_get_default_channel_layout(ac->channels),
ac->sample_fmt,
ac->sample_rate,
0,0 );
3、 re = swr_init(actx);
4、 //将一帧一帧的音频进行重采样 （参数对应输入输出）
int len = swr_convert(actx, //重采样上下文
out, //输出的指针
frame->nb_samples, //样本数量：单声道的样本数量
(const uint8_t**)frame->data,//解码出来的data
frame->nb_samples);//单通的样本数量
代码说明：
#include <jni.h> #include <string> #include <android/log.h> #include <android/native_window.h> #include <android/native_window_jni.h> #define LOGW(...) __android_log_print(ANDROID_LOG_WARN,"testff",__VA_ARGS__) extern "C"{ #include <libavcodec/avcodec.h> #include <libavformat/avformat.h> #include <libavcodec/jni.h> #include <libswscale/swscale.h> #include <libswresample/swresample.h> } #include<iostream> using namespace std; static double r2d(AVRational r) { return r.num==0||r.den == 0 ? 0 :(double)r.num/(double)r.den; } //当前时间戳 clock long long GetNowMs() { struct timeval tv; gettimeofday(&tv,NULL); int sec = tv.tv_sec%360000; long long t = sec*1000+tv.tv_usec/1000; return t; } extern "C" JNIEXPORT jint JNI_OnLoad(JavaVM *vm,void *res) { av_jni_set_java_vm(vm,0); return JNI_VERSION_1_4; } extern "C" JNIEXPORT jstring JNICALL Java_aplay_testffmpeg_MainActivity_stringFromJNI( JNIEnv *env, jobject /* this */) { std::string hello = "Hello from C++ "; // TODO hello += avcodec_configuration(); return env->NewStringUTF(hello.c_str()); } extern "C" JNIEXPORT void JNICALL Java_aplay_testffmpeg_XPlay_Open(JNIEnv *env, jobject instance, jstring url_, jobject surface) { const char *path = env->GetStringUTFChars(url_, 0); //初始化解封装 av_register_all(); //初始化网络 avformat_network_init(); avcodec_register_all(); //打开文件 AVFormatContext *ic = NULL; //char path[] = "/sdcard/video.flv"; int re = avformat_open_input(&ic,path,0,0); if(re != 0) { LOGW("avformat_open_input failed!:%s",av_err2str(re)); return; } LOGW("avformat_open_input %s success!",path); //获取流信息 re = avformat_find_stream_info(ic,0); if(re != 0) { LOGW("avformat_find_stream_info failed!"); } LOGW("duration = %lld nb_streams = %d",ic->duration,ic->nb_streams); int fps = 0; int videoStream = 0; int audioStream = 1; for(int i = 0; i < ic->nb_streams; i++) { AVStream *as = ic->streams[i]; if(as->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) { LOGW("视频数据"); videoStream = i; fps = r2d(as->avg_frame_rate); LOGW("fps = %d,width=%d height=%d codeid=%d pixformat=%d",fps, as->codecpar->width, as->codecpar->height, as->codecpar->codec_id, as->codecpar->format ); } else if(as->codecpar->codec_type ==AVMEDIA_TYPE_AUDIO ) { LOGW("音频数据"); audioStream = i; LOGW("sample_rate=%d channels=%d sample_format=%d", as->codecpar->sample_rate, as->codecpar->channels, as->codecpar->format ); } } //ic->streams[videoStream]; //获取音频流信息 audioStream = av_find_best_stream(ic,AVMEDIA_TYPE_AUDIO,-1,-1,NULL,0); LOGW("av_find_best_stream audioStream = %d",audioStream); ////////////////////////////////////////////////////////// //打开视频解码器 //软解码器 AVCodec *codec = avcodec_find_decoder(ic->streams[videoStream]->codecpar->codec_id); //硬解码 codec = avcodec_find_decoder_by_name("h264_mediacodec"); if(!codec) { LOGW("avcodec_find failed!"); return; } //解码器初始化 AVCodecContext *vc = avcodec_alloc_context3(codec); avcodec_parameters_to_context(vc,ic->streams[videoStream]->codecpar); vc->thread_count = 8; //打开解码器 re = avcodec_open2(vc,0,0); //vc->time_base = ic->streams[videoStream]->time_base; LOGW("vc timebase = %d/ %d",vc->time_base.num,vc->time_base.den); if(re != 0) { LOGW("avcodec_open2 video failed!"); return; } ////////////////////////////////////////////////////////// //打开音频解码器 //软解码器 AVCodec *acodec = avcodec_find_decoder(ic->streams[audioStream]->codecpar->codec_id); //硬解码 //codec = avcodec_find_decoder_by_name("h264_mediacodec"); if(!acodec) { LOGW("avcodec_find failed!"); return; } //音频解码器初始化 AVCodecContext *ac = avcodec_alloc_context3(acodec); avcodec_parameters_to_context(ac,ic->streams[audioStream]->codecpar); ac->thread_count = 8; //打开解码器 re = avcodec_open2(ac,0,0); if(re != 0) { LOGW("avcodec_open2 audio failed!"); return; } //读取帧数据 AVPacket *pkt = av_packet_alloc(); AVFrame *frame = av_frame_alloc(); long long start = GetNowMs(); int frameCount = 0; //初始化像素格式转换的上下文 SwsContext *vctx = NULL; int outWidth = 1280; int outHeight = 720; char *rgb = new char[1920*1080*4]; char *pcm = new char[48000*4*2]; //音频重采样上下文初始化 SwrContext *actx = swr_alloc(); actx = swr_alloc_set_opts(actx, av_get_default_channel_layout(2), AV_SAMPLE_FMT_S16,ac->sample_rate, av_get_default_channel_layout(ac->channels), ac->sample_fmt,ac->sample_rate, 0,0 ); re = swr_init(actx); if(re != 0) { LOGW("swr_init failed!"); } else { LOGW("swr_init success!"); } //显示窗口初始化 ANativeWindow *nwin = ANativeWindow_fromSurface(env,surface); ANativeWindow_setBuffersGeometry(nwin,outWidth,outHeight,WINDOW_FORMAT_RGBA_8888); ANativeWindow_Buffer wbuf; for(;;) { //超过三秒 if(GetNowMs() - start >= 3000) { LOGW("now decode fps is %d",frameCount/3); start = GetNowMs(); frameCount = 0; } int re = av_read_frame(ic,pkt); if(re != 0) { LOGW("读取到结尾处!"); int pos = 20 * r2d(ic->streams[videoStream]->time_base); av_seek_frame(ic,videoStream,pos,AVSEEK_FLAG_BACKWARD|AVSEEK_FLAG_FRAME ); continue; } AVCodecContext *cc = vc; if(pkt->stream_index == audioStream) cc=ac; //发送到线程中解码 re = avcodec_send_packet(cc,pkt); //清理 int p = pkt->pts; av_packet_unref(pkt); if(re != 0) { LOGW("avcodec_send_packet failed!"); continue; } for(;;) { re = avcodec_receive_frame(cc,frame); if(re !=0) { //LOGW("avcodec_receive_frame failed!"); break; } //LOGW("avcodec_receive_frame %lld",frame->pts); //如果是视频帧 if(cc == vc) { frameCount++; vctx = sws_getCachedContext(vctx, frame->width, frame->height, (AVPixelFormat)frame->format, outWidth, outHeight, AV_PIX_FMT_RGBA, SWS_FAST_BILINEAR, 0,0,0 ); if(!vctx) { LOGW("sws_getCachedContext failed!"); } else { uint8_t *data[AV_NUM_DATA_POINTERS] = {0}; data[0] =(uint8_t *)rgb; int lines[AV_NUM_DATA_POINTERS] = {0}; lines[0] = outWidth * 4; int h = sws_scale(vctx, (const uint8_t **)frame->data, frame->linesize,0, frame->height, data,lines); LOGW("sws_scale = %d",h); if(h > 0) { ANativeWindow_lock(nwin,&wbuf,0); uint8_t *dst = (uint8_t*)wbuf.bits; memcpy(dst,rgb,outWidth*outHeight*4); ANativeWindow_unlockAndPost(nwin); } } } else //音频 { uint8_t *out[2] = {0}; out[0] = (uint8_t*) pcm; //音频重采样 int len = swr_convert(actx,out, frame->nb_samples, (const uint8_t**)frame->data, frame->nb_samples); LOGW("swr_convert = %d",len); } } ////////////////////// } delete rgb; delete pcm; //关闭上下文 avformat_close_input(&ic); env->ReleaseStringUTFChars(url_, path); }