1. 注冊所有容器格式和CODEC:av_register_all()2. 打開文件:av_open_input_file()3. 從文件中提取流信息:av_find_stream_info()4. 窮舉所有的流，查找其中種類為CODEC_TYPE_VIDEO5. 查找對應的解碼器:avcodec_find_decoder()6. 打開編解碼器:avcodec_open()7. 為解碼幀分配內存:avcodec_alloc_frame()8. 不停地從碼流中提取出幀數據:av_read_frame()9. 判斷幀的類型，對于視頻幀調用:avcodec_decode_video()10. 解碼完后，釋放解碼器:avcodec_close()11. 關閉輸入文件:av_close_input_file()

FfmpegEncoder.h

/* * FfmpegEncoder.h * * Current, Can Support YUV422sp encoder and decoder * *  Created on: Dec 5, 2010 *      Author: Henry.Wen*/#ifndef _H264ENCODER_H#define _H264ENCODER_Hvoid save_image(const char* filePath, const void* bufferBase, int width, int height);int encoder_init(const char* filePath, int width, int height);int encoder_frame(const void* frame);int encoder_frame_yuv422(const void* frame);void encoder_close();#endif

　FfmpegEncoder.cpp

#include <math.h>#include <stdio.h>#include <stdlib.h>#include <string.h>extern "C"{#include <libavutil/mathematics.h>#include <libavformat/avformat.h>//#include <libswscale/swscale.h>}#include <skia/core/SkBitmap.h>#include <skia/images/SkImageEncoder.h>#include <android_runtime/AndroidRuntime.h>#include "FfmpegEncoder.h"AVOutputFormat   *g_fmt           = 0;AVFormatContext  *g_oc            = 0;AVCodec          *g_video_codec   = 0;AVStream         *g_video_st      = 0;AVFrame          *g_frame         = 0;AVPicture         g_picture;int               g_frame_count   = 0;double            g_video_pts     = 0;int               g_flagInit      = 0;int               g_width         = 0;int               g_height        = 0;using namespace android;static Mutex sg_mutexLock;#ifndef LOGI#define LOGI(...) ((void)__android_log_PRint(ANDROID_LOG_INFO,  "H264ENCODE", __VA_ARGS__))#define LOGE(...) ((void)__android_log_print(ANDROID_LOG_ERROR, "H264ENCODE", __VA_ARGS__))#endifvoid save_image(const char* filePath, const void* bufferBase, int width, int height){Mutex::Autolock lock(sg_mutexLock);SkBitmap b;#if (ANDROID_r4_4_0)b.setConfig(SkBitmap::kARGB_8888_Config, width, height,(size_t)0);#elseb.setConfig(SkBitmap::kARGB_8888_Config, width, height);#endifb.setPixels((void*)bufferBase);SkImageEncoder::EncodeFile(filePath, b, SkImageEncoder::kJPEG_Type, SkImageEncoder::kDefaultQuality);LOGI("save_image image ok====================");}AVStream *add_stream(AVFormatContext *oc, AVCodec **codec, enum AVCodecID codec_id, int width, int height){    AVCodecContext *c;    AVStream *st;    /* find the encoder */    *codec = avcodec_find_encoder(codec_id);    LOGI("encoder_init add_stream find encoder='%s'", avcodec_get_name(codec_id));    if (!(*codec))    {    LOGE("encoder_init add_stream could not find encoder for '%s'/n", avcodec_get_name(codec_id));    return 0;    }    st = avformat_new_stream(oc, *codec);    if (!st)    {    LOGE("encoder_init add_stream could not allocate stream");    return 0;    }    st->id = oc->nb_streams-1;    c = st->codec;    avcodec_get_context_defaults3(c, *codec);c->codec_id      = codec_id;//AV_CODEC_ID_MPEG4;c->bit_rate      = 40000;/* Resolution must be a multiple of two. */c->width         = width;c->height        = height;c->time_base.den = 25;c->time_base.num = 1;c->gop_size      = 12; /* emit one intra frame every twelve frames at most */c->pix_fmt       = AV_PIX_FMT_YUV420P;if (c->codec_id == AV_CODEC_ID_MPEG2VIDEO){c->max_b_frames = 2;}if (c->codec_id == AV_CODEC_ID_MPEG1VIDEO){c->mb_decision = 2;}    /* Some formats want stream headers to be separate. */    if (oc->oformat->flags & AVFMT_GLOBALHEADER)        c->flags |= CODEC_FLAG_GLOBAL_HEADER;    if(!strcmp(oc->oformat->name, "mp4") || !strcmp(oc->oformat->name, "mov") || !strcmp(oc->oformat->name, "3gp"))    c->flags |= CODEC_FLAG_GLOBAL_HEADER;    return st;}AVFrame* alloc_picture(AVPixelFormat pix_fmt, int width, int height){AVFrame *picture;uint8_t *picture_buf;int size;picture = avcodec_alloc_frame();if (!picture)return NULL;size = avpicture_get_size(pix_fmt, width, height);picture_buf = (uint8_t *)av_malloc(size);if (!picture_buf){av_free(picture);return NULL;}avpicture_fill((AVPicture *)picture, picture_buf, pix_fmt, width, height);return picture;}int open_video(AVFormatContext *oc, AVCodec *codec, AVStream *st){    int ret = 0;    AVCodecContext *c = st->codec;    /* open the codec */    ret = avcodec_open2(c, codec, NULL);    if (ret < 0)    {    LOGE("encoder_init open_video could not open video codec: %s", av_err2str(ret));    return -1;    }    g_frame = avcodec_alloc_frame();if (!g_frame){LOGE("encoder_init open_video could not allocate video frame");return -1;}ret = avpicture_alloc(&g_picture, c->pix_fmt, c->width, c->height);if (ret < 0){LOGE("encoder_init open_video could not allocate picture: %s", av_err2str(ret));free(g_frame);g_frame = 0;return -1;}*((AVPicture *)g_frame) = g_picture;    return 0;}void close_video(AVStream *st){if(st->codec){avcodec_close(st->codec);st->codec = 0;}if(g_frame){av_free(g_picture.data[0]);av_free(g_frame);g_frame = 0;}}int encoder_init(const char* filePath, int width, int height){if(g_flagInit)return 0;Mutex::Autolock lock(sg_mutexLock);int ret = 0;LOGI("encoder_init ============begin");if(!filePath || width <= 0 || height <= 0){LOGE("encoder_init input parameters error ret = %d", (ret = -1));return -1;}av_register_all();/* allocate the output media context */avformat_alloc_output_context2(&g_oc, NULL, NULL, filePath);if (!g_oc){LOGI("Could not deduce output format from file extension: using MPEG.");return -1;}g_fmt = g_oc->oformat;g_video_st = add_stream(g_oc, &g_video_codec, g_fmt->video_codec, width, height);av_dump_format(g_oc, 0, filePath, 1);if (g_video_st){if(open_video(g_oc, g_video_codec, g_video_st) < 0){LOGE("encoder_init open_video fail!");close_video(g_video_st);av_free(g_oc);g_oc = 0;return -1;}}else{LOGE("encoder_init g_video_st is null, not enough memory!");av_free(g_oc);g_oc = 0;return -1;}/* open the output file, if needed */if (!(g_fmt->flags & AVFMT_NOFILE)){LOGI("encoder_init avio_open ============begin");ret = avio_open(&g_oc->pb, filePath, AVIO_FLAG_WRITE);LOGI("encoder_init avio_open ret:%d============end", ret);if (ret < 0){LOGE("encoder_init could not open '%s': %s", filePath, av_err2str(ret));close_video(g_video_st);av_free(g_oc);g_oc = 0;return -1;}}LOGI("encoder_init avformat_write_header video file");ret = avformat_write_header(g_oc, NULL);if (ret < 0){LOGE("encoder_init error occurred when opening output file: %s/n", av_err2str(ret));close_video(g_video_st);av_free(g_oc);g_oc = 0;return -1;}if (g_frame)g_frame->pts = 0;g_flagInit  = 1;g_width     = width;g_height    = height;LOGI("encoder_init ============end");return 0;}static struct SwsContext *swsContext;void fill_yuv_image(AVFrame *pict, const void* frame){    int x, y, tmpIndex = 0, tmpWdith = g_width >> 1, tmpHeight = g_height >> 1;    unsigned char* tmpBuffer_yuv = (unsigned char*)frame;    /* Y */    for (y = 0; y < g_height; ++y)    {        for (x = 0; x < g_width; ++x)        {            pict->data[0][y * pict->linesize[0] + x] = *(tmpBuffer_yuv + tmpIndex);            ++tmpIndex;        }    }    tmpIndex = 0;    int tmpLength = g_width * g_height;    unsigned char* tmpBuffer_uv = tmpBuffer_yuv + tmpLength;    /* Cb and Cr */    for (y = 0; y < tmpHeight; ++y)    {        for (x = 0; x < tmpWdith; ++x)        {            pict->data[1][y * pict->linesize[1] + x] = *(tmpBuffer_uv + tmpIndex + 1);            pict->data[2][y * pict->linesize[2] + x] = *(tmpBuffer_uv + tmpIndex);            tmpIndex+= 2;        }    }}//fill AVFrame with YUV422p buffervoid fill_yuv422p_image(AVFrame *pict, const void* frameYUV422p){int width = g_width, height = g_height;unsigned char * pyuv422 = (unsigned char *)frameYUV422p;unsigned char * pyuv420y = &pict->data[0][0];unsigned char * pyuv420u= &pict->data[1][0];unsigned char * pyuv420v= &pict->data[2][0];int uv_count = 0;int i, j;for (i = 0; i < height; i += 2)for (j = 0; j < width; j += 2) {memcpy(pyuv420y + i * width + j, pyuv422 + i * width * 2 + j * 2,1);memcpy(pyuv420y + (i + 1) * width + j,pyuv422 + (i + 1) * width * 2 + j * 2, 1);memcpy(pyuv420y + i * width + (j + 1),pyuv422 + i * width * 2 + (j + 1) * 2, 1);memcpy(pyuv420y + (i + 1) * width + (j + 1),pyuv422 + (i + 1) * width * 2 + (j + 1) * 2, 1);//±£ÁôU ·ÖÁ¿memcpy(pyuv420u + uv_count, pyuv422 + i * width * 2 + j * 2 + 1, 1);//±£ÁôV·ÖÁ¿;memcpy(pyuv420v + uv_count,pyuv422 + (i + 1) * width * 2 + (j + 1) * 2 + 1, 1);uv_count++;}/*int x, y, tmpIndex = 0, tmpWdith = g_width >> 1, tmpHeight = g_height >> 1;unsigned char* tmpBuffer_yuv = (unsigned char*)frameYUV422p;/* Y *//*for (y = 0; y < g_height; ++y){for (x = 0; x < g_width; ++x){pict->data[0][y * pict->linesize[0] + x] = *(tmpBuffer_yuv + tmpIndex);++tmpIndex;}}tmpIndex = 0;int tmpLength = g_width * g_height;unsigned char* tmpBuffer_uv = tmpBuffer_yuv + tmpLength;// Cb and Crfor (y = 0; y < tmpHeight; ++y){for (x = 0; x < tmpWdith; ++x){pict->data[1][y * pict->linesize[1] + x] = *(tmpBuffer_uv + tmpIndex);pict->data[2][y * pict->linesize[2] + x] = *(tmpBuffer_uv + tmpIndex +1);tmpIndex += 2;}tmpIndex += g_width;}*/}void write_video_frame(AVFormatContext *oc, AVStream *st){    int ret;    static struct SwsContext *sws_ctx;    AVCodecContext *c = st->codec;    /* encode the image */AVPacket pkt;int got_output;av_init_packet(&pkt);pkt.data = NULL;    // packet data will be allocated by the encoderpkt.size = 0;ret = avcodec_encode_video2(c, &pkt, g_frame, &got_output);if (ret < 0){LOGE("encoder_init error encoding video frame: %s/n", av_err2str(ret));return;}//If size is zero, it means the image was buffered.if (got_output){   if (c->coded_frame->key_frame)   pkt.flags |= AV_PKT_FLAG_KEY;   pkt.stream_index = st->index;   ret = av_interleaved_write_frame(oc, &pkt);}else{   ret = 0;}av_free_packet(&pkt);    if (ret != 0)    {        LOGE("encoder_init error while writing video frame: %s/n", av_err2str(ret));        return;    }    ++g_frame_count = 0;}int encoder_frame(const void* frame){if(!g_flagInit)return 0;Mutex::Autolock lock(sg_mutexLock);fill_yuv_image(g_frame, frame);if (g_video_st)g_video_pts = (double)g_video_st->pts.val * g_video_st->time_base.num / g_video_st->time_base.den;elseg_video_pts = 0.0;write_video_frame(g_oc, g_video_st);g_frame->pts += av_rescale_q(1, g_video_st->codec->time_base, g_video_st->time_base);return 0;}int encoder_frame_yuv422(const void* frame){if(!g_flagInit)return 0;Mutex::Autolock lock(sg_mutexLock);fill_yuv422p_image(g_frame, frame);if (g_video_st)g_video_pts = (double)g_video_st->pts.val * g_video_st->time_base.num / g_video_st->time_base.den;elseg_video_pts = 0.0;write_video_frame(g_oc, g_video_st);g_frame->pts += av_rescale_q(1, g_video_st->codec->time_base, g_video_st->time_base);return 0;}void encoder_close(){LOGI("encoder_close ============begin");Mutex::Autolock lock(sg_mutexLock);if(g_oc){av_write_trailer(g_oc);if (g_video_st)close_video(g_video_st);for(int i = 0; i < (int)g_oc->nb_streams; ++i){av_freep(&g_oc->streams[i]->codec);av_freep(&g_oc->streams[i]);}if (!(g_fmt->flags & AVFMT_NOFILE))avio_close(g_oc->pb);av_free(g_oc);}g_oc            = 0;g_video_st      = 0;g_flagInit      = 0;g_frame_count   = 0;g_width         = 0;g_height        = 0;LOGI("encoder_close ============end");}

　　首先第一件事情就是開一個視頻文件并從中得到流。我們要做的第一件事情就是使用av_register_all();來初始化libavformat/libavcodec:

這一步注冊庫中含有的所有可用的文件格式和編碼器，這樣當打開一個文件時，它們才能夠自動選擇相應的文件格式和編碼器。av_register_all()只需調用一次，所以，要放在初始化代碼中。也可以僅僅注冊個人的文件格式和編碼?！　∠乱徊?，打開文件：AVFormatContext *pFormatCtx;const char *filename="myvideo.mpg";av_open_input_file(&pFormatCtx, filename, NULL, 0, NULL)； // 打開視頻文件最后三個參數描述了文件格式，緩沖區大?。╯ize）和格式參數；我們通過簡單地指明NULL或0告訴 libavformat 去自動探測文件格式并且使用默認的緩沖區大小。這里的格式參數指的是視頻輸出參數，比如寬高的坐標。　　下一步，我們需要取出包含在文件中的流信息：av_find_stream_info(pFormatCtx)； // 取出流信息AVFormatContext 結構體dump_format(pFormatCtx, 0, filename, false);//我們可以使用這個函數把獲取到得參數全部輸出。for(i=0; i<pFormatCtx->nb_streams; i++) //區分視頻流和音頻流 if(pFormatCtx->streams->codec.codec_type==CODEC_TYPE_VIDEO) //找到視頻流，這里也可以換成音頻 { videoStream=i; break; }接下來就需要尋找解碼器AVCodec *pCodec;pCodec=avcodec_find_decoder(pCodecCtx->codec_id);avcodec_open(pCodecCtx, pCodec)； // 打開解碼器給視頻幀分配空間以便存儲解碼后的圖片：AVFrame *pFrame;pFrame=avcodec_alloc_frame();/////////////////////////////////////////開始解碼///////////////////////////////////////////第一步當然是讀數據：我們將要做的是通過讀取包來讀取整個視頻流，然后把它解碼成幀，最后轉換格式并且保存。while(av_read_frame(pFormatCtx, &packet)>=0) { //讀數據 if(packet.stream_index==videoStream){ //判斷是否視頻流 avcodec_decode_video(pCodecCtx,pFrame, &frameFinished,packet.data, packet.size); //解碼 if(frameFinished) {img_convert((AVPicture *)pFrameRGB, PIX_FMT_RGB24,(AVPicture*)pFrame, pCodecCtx->pix_fmt, pCodecCtx->width,pCodecCtx->height);//轉換 SaveFrame(pFrameRGB, pCodecCtx->width,pCodecCtx->height, i); //保存數據av_free_packet(&packet); //釋放av_read_frame()讀取一個包并且把它保存到AVPacket結構體中。這些數據可以在后面通過av_free_packet()來釋 放。函數avcodec_decode_video()把包轉換為幀。然而當解碼一個包的時候，我們可能沒有得到我們需要的關于幀的信息。因此，當我們得 到下一幀的時候，avcodec_decode_video()為我們設置了幀結束標志frameFinished。最后，我們使用 img_convert()函數來把幀從原始格式（pCodecCtx->pix_fmt）轉換成為RGB格式。要記住，你可以把一個 AVFrame結構體的指針轉換為AVPicture結構體的指針。最后，我們把幀和高度寬度信息傳遞給我們的SaveFrame函數。到此解碼完畢，顯示過程使用SDL完成考慮到我們以后會使用firmware進行顯示操作，SDL忽略不講。音視頻同步DTS（解碼時間戳）和PTS（顯示時間戳）當我們調用av_read_frame()得到一個包的時候，PTS和DTS的信息也會保存在包中。但是我們真正想要的PTS是我們剛剛解碼出來的 原始幀 的PTS，這樣我們才能知道什么時候來顯示它。然而，我們從avcodec_decode_video()函數中得到的幀只是一個AVFrame，其中并 沒有包含有用的PTS值（注意：AVFrame并沒有包含時間戳信息，但當我們等到幀的時候并不是我們想要的樣子）。。我們保存一幀的第一個包的PTS： 這將作為整個這一幀的PTS。我們 可以通過函數avcodec_decode_video()來計算出哪個包是一幀的第一個包。怎樣實現呢？任何時候當一個包開始一幀的時 候，avcodec_decode_video()將調用一個函數來為一幀申請一個緩沖。當然，ffmpeg允許我們重新定義那個分配內存的函數。計算前 一幀和現在這一幀的時間戳來預測出下一個時間戳的時間。同時，我們需要同步視頻到音頻。我們將設置一個音頻時間audioclock；一個內部值記錄了我 們正在播放的音頻的位置。就像從任意的mp3播放器中讀出來的數字一樣。既然我們把視頻同步到音頻，視頻線程使用這個值來算出是否太快還是太慢。