使用FFmpeg获取PCM和YUV数据的流程基本上一样的，下面就以获取YUV数据的流程为例，说明这个过程：
- 初始化AVFormatContext 。
- 打开文件，获取流信息，获取视频流/音频流。
- 找到解码器，并且初始化解码器。
- 初始化AVPacket ，AVFrame ，和buffer。
- 对输出格式进行规范，如视频的宽高，音频的采用率，声道数等。
- 读取一帧数据，然后把数据写入到文件。
- 读完数据后，释放内存。
#include <jni.h>
#include <string.h>
#include <stdlib.h>
#include "android/log.h"
extern "C"{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libswresample/swresample.h"
};
#define LOGD(FORMAT,...) __android_log_print(ANDROID_LOG_INFO,"jni",FORMAT,##__VA_ARGS__);
extern "C"
JNIEXPORT jint JNICALL
Java_audioplayer_MainActivity_getYuvData(JNIEnv *env, jobject instance, jstring srcPath_,
jstring desPath_) {
const char *srcPath = env->GetStringUTFChars(srcPath_, 0);
const char *desPath = env->GetStringUTFChars(desPath_, 0);
AVFormatContext *pFormatCtx;
int i,videoIndex;
AVCodecContext *pCodecCtx;
AVCodec *pCodec;
/* init */
av_register_all();
avformat_network_init();
pFormatCtx = avformat_alloc_context();
/* open file,find streams,and then find a video stream */
if(avformat_open_input(&pFormatCtx,srcPath,NULL,NULL)!=0){
LOGD("Couldn't open input stream.");
return -1;
}
if(avformat_find_stream_info(pFormatCtx,NULL)<0){
LOGD("Couldn't find stream information.");
return -1;
}
videoIndex = -1;
for(i=0;i<pFormatCtx->nb_streams;i++){
if(pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO){
videoIndex = i;
break;
}
}
if(videoIndex == -1){
LOGD("Don't find a video stream.");
return -1;
}
/* find a decoder */
pCodecCtx = pFormatCtx->streams[videoIndex]->codec;
pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
if(pCodec == NULL){
LOGD("Codec not found.\n");
return -1;
}
if(avcodec_open2(pCodecCtx,pCodec,NULL)<0){
LOGD("Could not open codec.");
return -1;
}
LOGD("File format: %s.\nVideo duration: %lld.\nVideo width: %d,Video height: %d.",
pFormatCtx->iformat->name,pFormatCtx->duration,pCodecCtx->width,pCodecCtx->height);
/* init Buffer */
AVPacket *packet = (AVPacket *)malloc(sizeof(AVPacket));
AVFrame *pFrame = av_frame_alloc();
AVFrame *pFrameYuv = av_frame_alloc();
uint8_t *out_buffer = (uint8_t *)av_malloc(avpicture_get_size(AV_PIX_FMT_YUV420P,pCodecCtx->width,pCodecCtx->height));
avpicture_fill((AVPicture *)pFrameYuv,out_buffer,AV_PIX_FMT_YUV420P,pCodecCtx->width,pCodecCtx->height);
struct SwsContext *swsContext= sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
int ret,got_picture;
FILE *fp = fopen(desPath,"wb+");
int frame_cnt = 0;
/* ever time read a frame and decode it */
while(av_read_frame(pFormatCtx,packet)>=0){
if(packet->stream_index == videoIndex){
ret = avcodec_decode_video2(pCodecCtx,pFrame,&got_picture,packet);
if(ret < 0){
LOGD("Decode Error.");
return -1;
}
if(got_picture){
sws_scale(swsContext, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
pFrameYuv->data, pFrameYuv->linesize);
LOGD("Decoded frame index: %d\n",frame_cnt);
fwrite(pFrameYuv->data[0],1,pCodecCtx->width * pCodecCtx->height,fp);
fwrite(pFrameYuv->data[1],1,pCodecCtx->width * pCodecCtx->height / 4,fp);
fwrite(pFrameYuv->data[2],1,pCodecCtx->width * pCodecCtx->height / 4,fp);
fflush(fp);
frame_cnt++;
}
}
av_free_packet(packet);
}
LOGD("Decode end");
fclose(fp);
sws_freeContext(swsContext);
av_frame_free(&pFrameYuv);
av_frame_free(&pFrame);
avcodec_close(pCodecCtx);
avformat_close_input(&pFormatCtx);
env->ReleaseStringUTFChars(srcPath_, srcPath);
env->ReleaseStringUTFChars(desPath_, desPath);
return 0;
}
extern "C"
JNIEXPORT jint JNICALL
Java_audioplayer_MainActivity_getPcmData(JNIEnv *env, jobject instance, jstring srcPath_,
jstring desPath_) {
const char *srcPath = env->GetStringUTFChars(srcPath_, 0);
const char *desPath = env->GetStringUTFChars(desPath_, 0);
AVFormatContext *pFormatCtx;
int i,audioIndex;
AVCodecContext *pCodecCtx;
AVCodec *pCodec;
/* init */
av_register_all();
avformat_network_init();
pFormatCtx = avformat_alloc_context();
/* open file,find streams,and then find a video stream */
if(avformat_open_input(&pFormatCtx,srcPath,NULL,NULL)!=0){
LOGD("Couldn't open input stream.");
return -1;
}
if(avformat_find_stream_info(pFormatCtx,NULL)<0){
LOGD("Couldn't find stream information.");
return -1;
}
audioIndex = -1;
for(i=0;i<pFormatCtx->nb_streams;i++){
if(pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO){
audioIndex = i;
break;
}
}
if(audioIndex == -1){
LOGD("Don't find a video stream.");
return -1;
}
/* find a decoder */
pCodecCtx = pFormatCtx->streams[audioIndex]->codec;
pCodec = avcodec_find_decoder(pCodecCtx->codec_id);
if(pCodec == NULL){
LOGD("Codec not found.\n");
return -1;
}
if(avcodec_open2(pCodecCtx,pCodec,NULL)<0){
LOGD("Could not open codec.");
return -1;
}
LOGD("File format: %s.\nVideo duration: %lld.\nVideo width: %d,Video height: %d.",
pFormatCtx->iformat->name,pFormatCtx->duration,pCodecCtx->width,pCodecCtx->height);
/* init Buffer */
AVPacket *packet = (AVPacket *)malloc(sizeof(AVPacket));
AVFrame *pFrame = av_frame_alloc();
/* change sample rate and format to a standard format */
SwrContext *swrCtx = swr_alloc();
enum AVSampleFormat in_sample_fmt = pCodecCtx->sample_fmt;
enum AVSampleFormat out_sample_fmt = AV_SAMPLE_FMT_S16;
int in_sample_rate = pCodecCtx->sample_rate;
int out_sample_rate = 44100;
uint64_t in_ch_layout = pCodecCtx->channel_layout;
uint64_t out_ch_layout = AV_CH_LAYOUT_STEREO;
swr_alloc_set_opts(swrCtx,out_ch_layout,out_sample_fmt,out_sample_rate,
in_ch_layout,in_sample_fmt,in_sample_rate,0,NULL);
swr_init(swrCtx);
int out_channel_nb = av_get_channel_layout_nb_channels(out_ch_layout);
uint8_t *out_buffer = (uint8_t *) av_malloc(2 * 44100);
FILE *fp = fopen(desPath,"wb+");
int ret,got_frame,frame_cnt = 0;
while(av_read_frame(pFormatCtx,packet)>=0){
if(packet->stream_index == audioIndex){
ret = avcodec_decode_audio4(pCodecCtx,pFrame,&got_frame,packet);
if(ret < 0){
LOGD("Decode end");
}
if(got_frame){
LOGD("Decoded frame index: %d\n",frame_cnt);
swr_convert(swrCtx,&out_buffer,2 * 44100,(const uint8_t **)pFrame->data,pFrame->nb_samples);
int out_buffer_size = av_samples_get_buffer_size(NULL, out_channel_nb, pFrame->nb_samples, out_sample_fmt, 1);
fwrite(out_buffer, 1, out_buffer_size, fp);
fflush(fp);
frame_cnt++;
}
}
av_free_packet(packet);
}
LOGD("Decode finish");
fclose(fp);
swr_free(&swrCtx);
av_frame_free(&pFrame);
avcodec_close(pCodecCtx);
avformat_close_input(&pFormatCtx);
env->ReleaseStringUTFChars(srcPath_, srcPath);
env->ReleaseStringUTFChars(desPath_, desPath);
return 0;
}
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