4 FFmpeg4Android：視頻解碼
4.1 視頻解碼流程
a) 視頻播放流程
視頻播放器播放視頻文件陆盘，需要經(jīng)過以下幾個(gè)步驟：解封裝奈揍，解碼視音頻拥褂，視音頻同步镇匀。如果播放本地文件則不需要解協(xié)議，為以下幾個(gè)步驟：解封裝，解碼視音頻序目，視音頻同步臂痕。他們的過程如圖所示。
視頻播放流程
（參考雷神博客：[總結(jié)]視音頻編解碼技術(shù)零基礎(chǔ)學(xué)習(xí)方法）
b) 解碼流程
解碼流程
解碼者是這固定的幾個(gè)流程猿涨，只要按照這個(gè)固定模式來調(diào)用函數(shù)即可握童，下面是各函數(shù)的作用：
av_register_all()：注冊(cè)所有組件
avformat_open_input()：打開輸入視頻文件
avformat_find_stream_info()：獲取視頻文件信息
avcodec_find_decoder()：查找解碼器
avcodec_open2()：打開解碼器
av_read_frame()：從輸入文件讀取一幀壓縮數(shù)據(jù)
avcodec_decode_video2()：解碼一幀壓縮數(shù)據(jù)
接下來的4.2、4.3分別介紹視頻叛赚、音頻的解碼過程
4.2 視頻解碼
該實(shí)例實(shí)現(xiàn)的作用為澡绩，將.mp4文件轉(zhuǎn)換成.yuv文件。
項(xiàng)目目錄結(jié)構(gòu)：
目錄結(jié)構(gòu)
Java端代碼俺附，MainActivity.java：
package com.lzp.sffmpegandroiddecoder;
import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button startButton = (Button) this.findViewById(R.id.button_start);
final EditText urlEdittext_input= (EditText) this.findViewById(R.id.input_url);
final EditText urlEdittext_output= (EditText) this.findViewById(R.id.output_url);
startButton.setOnClickListener(new OnClickListener() {
public void onClick(View arg0){
String folderurl=Environment.getExternalStorageDirectory().getPath();
String urltext_input=urlEdittext_input.getText().toString();
String inputurl=folderurl+"/"+urltext_input;
Log.e("path", inputurl);
String urltext_output=urlEdittext_output.getText().toString();
String outputurl=folderurl+"/"+urltext_output;
Log.i("inputurl",inputurl);
Log.i("outputurl",outputurl);
decode(inputurl,outputurl);
}
});
}
//JNI
public native int decode(String inputurl, String outputurl);
static{
System.loadLibrary("avutil-54");
System.loadLibrary("swresample-1");
System.loadLibrary("avcodec-56");
System.loadLibrary("avformat-56");
System.loadLibrary("swscale-3");
System.loadLibrary("postproc-53");
System.loadLibrary("avfilter-5");
System.loadLibrary("avdevice-56");
System.loadLibrary("sffdecoder");
}
}
C端源代碼位于jni/simplest_ffmpeg_decoder.c肥卡，其負(fù)責(zé)對(duì)*.mp4文件的解碼操作，根據(jù)上節(jié)中視頻解碼流程事镣，實(shí)現(xiàn)過的代碼如下所示：
#include <stdio.h>
#include <time.h>
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libavutil/log.h"
#ifdef ANDROID
#include <jni.h>
#include <android/log.h>
#define LOGE(format, ...) __android_log_print(ANDROID_LOG_ERROR, "(>_<)", format, ##__VA_ARGS__)
#define LOGI(format, ...) __android_log_print(ANDROID_LOG_INFO, "(^_^)", format, ##__VA_ARGS__)
#else
#define LOGE(format, ...) printf("(>_<) " format "\n", ##__VA_ARGS__)
#define LOGI(format, ...) printf("(^_^) " format "\n", ##__VA_ARGS__)
#endif
//Output FFmpeg's av_log()
void custom_log(void *ptr, int level, const char* fmt, va_list vl)
{
FILE *fp=fopen("/storage/emulated/0/av_log.txt","a+");
if(fp){
vfprintf(fp,fmt,vl);
fflush(fp);
fclose(fp);
}
}
JNIEXPORT jint JNICALL Java_com_lzp_sffmpegandroiddecoder_MainActivity_decode
(JNIEnv *env, jobject obj, jstring input_jstr, jstring output_jstr)
{
AVFormatContext *pFormatCtx;
int i, videoindex;
AVCodecContext *pCodecCtx;
AVCodec *pCodec;
AVFrame *pFrame,*pFrameYUV;
uint8_t *out_buffer;
AVPacket *packet;
int y_size;
int ret, got_picture;
struct SwsContext *img_convert_ctx;
FILE *fp_yuv;
int frame_cnt;
clock_t time_start, time_finish;
double time_duration = 0.0;
char input_str[500]={0};
char output_str[500]={0};
char info[1000]={0};
sprintf(input_str,"%s",(*env)->GetStringUTFChars(env,input_jstr, NULL));
sprintf(output_str,"%s",(*env)->GetStringUTFChars(env,output_jstr, NULL));
//FFmpeg av_log() callback
av_log_set_callback(custom_log);
av_register_all();
avformat_network_init();
pFormatCtx = avformat_alloc_context();
if(avformat_open_input(&pFormatCtx,input_str,NULL,NULL)!=0){
LOGE("Couldn't open input stream.\n");
return -1;
}
if(avformat_find_stream_info(pFormatCtx,NULL)<0){
LOGE("Couldn't find stream information.\n");
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){
LOGE("Couldn't find a video stream.\n");
return -1;
}
pCodecCtx=pFormatCtx->streams[videoindex]->codec;
pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
if(pCodec==NULL){
LOGE("Couldn't find Codec.\n");
return -1;
}
if(avcodec_open2(pCodecCtx, pCodec,NULL)<0){
LOGE("Couldn't open codec.\n");
return -1;
}
pFrame=av_frame_alloc();
pFrameYUV=av_frame_alloc();
out_buffer=(unsigned char *)av_malloc(av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height,1));
av_image_fill_arrays(pFrameYUV->data, pFrameYUV->linesize,out_buffer,
AV_PIX_FMT_YUV420P,pCodecCtx->width, pCodecCtx->height,1);
packet=(AVPacket *)av_malloc(sizeof(AVPacket));
img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt,
pCodecCtx->width, pCodecCtx->height, AV_PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL);
sprintf(info, "[Input ]%s\n", input_str);
sprintf(info, "%s[Output ]%s\n",info,output_str);
sprintf(info, "%s[Format ]%s\n",info, pFormatCtx->iformat->name);
sprintf(info, "%s[Codec ]%s\n",info, pCodecCtx->codec->name);
sprintf(info, "%s[Resolution]%dx%d\n",info, pCodecCtx->width,pCodecCtx->height);
fp_yuv=fopen(output_str,"wb+");
if(fp_yuv==NULL){
printf("Cannot open output file.\n");
return -1;
}
frame_cnt=0;
time_start = clock();
while(av_read_frame(pFormatCtx, packet)>=0){
// 這里只要處理視頻幀
if(packet->stream_index==videoindex){
ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
if(ret < 0){
LOGE("Decode Error.\n");
return -1;
}
if(got_picture){
sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
pFrameYUV->data, pFrameYUV->linesize);
y_size=pCodecCtx->width*pCodecCtx->height;
fwrite(pFrameYUV->data[0],1,y_size,fp_yuv); //Y
fwrite(pFrameYUV->data[1],1,y_size/4,fp_yuv); //U
fwrite(pFrameYUV->data[2],1,y_size/4,fp_yuv); //V
//Output info
char pictype_str[10]={0};
switch(pFrame->pict_type){
case AV_PICTURE_TYPE_I:sprintf(pictype_str,"I");break;
case AV_PICTURE_TYPE_P:sprintf(pictype_str,"P");break;
case AV_PICTURE_TYPE_B:sprintf(pictype_str,"B");break;
default:sprintf(pictype_str,"Other");break;
}
LOGI("Frame Index: %5d. Type:%s",frame_cnt,pictype_str);
frame_cnt++;
}
}
av_free_packet(packet);
}
//flush decoder
//FIX: Flush Frames remained in Codec
while (1)
{
ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
if (ret < 0)
break;
if (!got_picture)
break;
sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height,
pFrameYUV->data, pFrameYUV->linesize);
int y_size=pCodecCtx->width*pCodecCtx->height;
fwrite(pFrameYUV->data[0],1,y_size,fp_yuv); //Y
fwrite(pFrameYUV->data[1],1,y_size/4,fp_yuv); //U
fwrite(pFrameYUV->data[2],1,y_size/4,fp_yuv); //V
//Output info
char pictype_str[10]={0};
switch(pFrame->pict_type){
case AV_PICTURE_TYPE_I:sprintf(pictype_str,"I");break;
case AV_PICTURE_TYPE_P:sprintf(pictype_str,"P");break;
case AV_PICTURE_TYPE_B:sprintf(pictype_str,"B");break;
default:sprintf(pictype_str,"Other");break;
}
LOGI("Frame Index: %5d. Type:%s",frame_cnt,pictype_str);
frame_cnt++;
}
time_finish = clock();
time_duration=(double)(time_finish - time_start);
sprintf(info, "%s[Time ]%fms\n",info,time_duration);
sprintf(info, "%s[Count ]%d\n",info,frame_cnt);
sws_freeContext(img_convert_ctx);
fclose(fp_yuv);
av_frame_free(&pFrameYUV);
av_frame_free(&pFrame);
avcodec_close(pCodecCtx);
avformat_close_input(&pFormatCtx);
return 0;
}
Android.mk文件位于jni/Android.mk步鉴，如下所示：
LOCAL_PATH := $(call my-dir)
# FFmpeg library
include $(CLEAR_VARS)
LOCAL_MODULE := avcodec
LOCAL_SRC_FILES := libavcodec-56.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := avdevice
LOCAL_SRC_FILES := libavdevice-56.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := avfilter
LOCAL_SRC_FILES := libavfilter-5.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := avformat
LOCAL_SRC_FILES := libavformat-56.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := avutil
LOCAL_SRC_FILES := libavutil-54.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := postproc
LOCAL_SRC_FILES := libpostproc-53.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := swresample
LOCAL_SRC_FILES := libswresample-1.so
include $(PREBUILT_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_MODULE := swscale
LOCAL_SRC_FILES := libswscale-3.so
include $(PREBUILT_SHARED_LIBRARY)
# Program
include $(CLEAR_VARS)
LOCAL_MODULE := sffdecoder
LOCAL_SRC_FILES :=simplest_ffmpeg_decoder.c
LOCAL_C_INCLUDES += $(LOCAL_PATH)/include
LOCAL_LDLIBS := -llog -lz
LOCAL_SHARED_LIBRARIES := avcodec avdevice avfilter avformat avutil postproc swresample swscale
include $(BUILD_SHARED_LIBRARY)
build.gradle文件位于，如下所示：
import org.apache.tools.ant.taskdefs.condition.Os
apply plugin: 'com.android.application'
android {
compileSdkVersion 26
buildToolsVersion "26.0.1"
defaultConfig {
applicationId "com.lzp.sffmpegandroiddecoder"
minSdkVersion 15
targetSdkVersion 26
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
//指定動(dòng)態(tài)庫路徑
sourceSets {
main{
jni.srcDirs = [] // disable automatic ndk-build call, which ignore our Android.mk
jniLibs.srcDir 'src/main/libs'
}
}
// call regular ndk-build(.cmd) script from app directory
task ndkBuild(type: Exec) {
workingDir file('src/main')
commandLine getNdkBuildCmd()
//commandLine 'E:/Android/android-ndk-r10e/ndk-build.cmd' //也可以直接使用絕對(duì)路徑
}
tasks.withType(JavaCompile) {
compileTask -> compileTask.dependsOn ndkBuild
}
task cleanNative(type: Exec) {
workingDir file('src/main')
commandLine getNdkBuildCmd(), 'clean'
}
clean.dependsOn cleanNative
}
//獲取NDK目錄路徑
def getNdkDir() {
if (System.env.ANDROID_NDK_ROOT != null)
return System.env.ANDROID_NDK_ROOT
Properties properties = new Properties()
properties.load(project.rootProject.file('local.properties').newDataInputStream())
def ndkdir = properties.getProperty('ndk.dir', null)
if (ndkdir == null)
throw new GradleException("NDK location not found. Define location with ndk.dir in the local.properties file or with an ANDROID_NDK_ROOT environment variable.")
return ndkdir
}
//根據(jù)不同系統(tǒng)獲取ndk-build腳本
def getNdkBuildCmd() {
def ndkbuild = getNdkDir() + "/ndk-build"
if (Os.isFamily(Os.FAMILY_WINDOWS))
ndkbuild += ".cmd"
return ndkbuild
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
exclude group: 'com.android.support', module: 'support-annotations'
})
compile 'com.android.support:appcompat-v7:26.+'
compile 'com.android.support.constraint:constraint-layout:1.0.2'
testCompile 'junit:junit:4.12'
}
將sintel.mp4文件拷到手機(jī)SDK根目錄璃哟，運(yùn)行并點(diǎn)擊Star按鈕后氛琢，在AndroidMonitor中打印如下信息：
運(yùn)行結(jié)果
Type：I、P随闪、B是各視頻幀的類型阳似。
