17.FFmpeg学习笔记 - 解码视频

上篇文章用libavcodec API解码音频文件，本篇文章解码视频。

#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
#include <libavutil/imgutils.h>
#include <libavutil/samplefmt.h>
#include <libavutil/timestamp.h>


static uint8_t *video_dst_data[4] = {NULL};
static int video_dst_linesize[4];
static int video_dst_bufsize;

static int width;
static int height;
static const char *fmt_name = NULL;


#define VIDEO_INBUF_SIZE 20480
#define VIDEO_REFILL_THRESH 4096


static void decode(AVCodecContext *dec_ctx, AVPacket *pkt, AVFrame *frame,
                   FILE *outfile)
{
    int ret;
    
    /* send the packet with the compressed data to the decoder */
    ret = avcodec_send_packet(dec_ctx, pkt);
    if (ret < 0) {
        fprintf(stderr, "Error submitting the packet to the decoder\n");
        exit(1);
    }
    
    /* read all the output frames (in general there may be any number of them */
    while (ret >= 0) {
        ret = avcodec_receive_frame(dec_ctx, frame);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
            return;
        else if (ret < 0) {
            fprintf(stderr, "Error during decoding\n");
            exit(1);
        }
        
        if (!video_dst_data[0]) {
            
            width = frame->width;
            height = frame->height;
            fmt_name = av_get_pix_fmt_name(frame->format);
            
            ret = av_image_alloc(video_dst_data, video_dst_linesize, width, height, frame->format, 1);
            if (ret < 0) {
                printf("Could not allocate raw video buffer\n");
                exit(1);
            }
            video_dst_bufsize = ret;
        }
        
        //复制解码后的视频到之前创建的缓存区
        av_image_copy(video_dst_data, video_dst_linesize, (const uint8_t **)frame->data, frame->linesize, frame->format, frame->width, frame->height);
        
        //写入视频
        fwrite(video_dst_data[0], 1, video_dst_bufsize, outfile);
        
    }
}

static void decode_video(void)
{
    const char *infilename = "/Users/zhw/Desktop/sintel.h264";
    const char *outfilename = "/Users/zhw/Desktop/sintel.yuv";
    const AVCodec *codec;
    AVCodecContext *c= NULL;
    AVCodecParserContext *parser = NULL;
    size_t len, ret;
    FILE *f, *outfile;
    uint8_t inbuf[VIDEO_INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
    uint8_t *data;
    size_t   data_size;
    AVPacket *pkt;
    AVFrame *decoded_frame = NULL;
    
    pkt = av_packet_alloc();
    
    /* 此处应根据输入文件的实际编码格式选择正确的编码ID */
    codec = avcodec_find_decoder(AV_CODEC_ID_H264);
    if (!codec) {
        fprintf(stderr, "Codec not found\n");
        exit(1);
    }
    
    parser = av_parser_init(codec->id);
    if (!parser) {
        fprintf(stderr, "Parser not found\n");
        exit(1);
    }
    
    c = avcodec_alloc_context3(codec);
    if (!c) {
        fprintf(stderr, "Could not allocate video codec context\n");
        exit(1);
    }
    
    /* open it */
    if (avcodec_open2(c, codec, NULL) < 0) {
        fprintf(stderr, "Could not open codec\n");
        exit(1);
    }
    
    f = fopen(infilename, "rb");
    if (!f) {
        fprintf(stderr, "Could not open %s\n", infilename);
        exit(1);
    }
    outfile = fopen(outfilename, "wb");
    if (!outfile) {
        exit(1);
    }
    
    /* decode until eof */
    data      = inbuf;
    data_size = fread(inbuf, 1, VIDEO_INBUF_SIZE, f);
    
    while (data_size > 0) {
        if (!decoded_frame) {
            if (!(decoded_frame = av_frame_alloc())) {
                fprintf(stderr, "Could not allocate video frame\n");
                exit(1);
            }
        }
        
        ret = av_parser_parse2(parser, c, &pkt->data, &pkt->size,
                               data, (int)data_size,
                               AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
        if (ret < 0) {
            fprintf(stderr, "Error while parsing\n");
            exit(1);
        }
        data      += ret;
        data_size -= ret;
        
        if (pkt->size){
            decode(c, pkt, decoded_frame, outfile);
            av_packet_unref(pkt);
        }
        
        if (data_size < VIDEO_REFILL_THRESH) {
            memmove(inbuf, data, data_size);
            data = inbuf;
            len = fread(data + data_size, 1,
                        VIDEO_INBUF_SIZE - data_size, f);
            if (len > 0)
                data_size += len;
        }
    }
    
    /* flush the decoder */
    pkt->data = NULL;
    pkt->size = 0;
    decode(c, pkt, decoded_frame, outfile);
    av_packet_unref(pkt);
    
    fclose(outfile);
    fclose(f);
    
    avcodec_free_context(&c);
    av_parser_close(parser);
    av_frame_free(&decoded_frame);
    av_packet_free(&pkt);
    
    printf("finish decode video\n");
    printf("Play the output video file with the command:\n"
           "ffplay -f rawvideo -pixel_format %s -video_size %dx%d %s\n",
           fmt_name, width, height,
           outfilename);

    
}