ffmpeg 解码示例

相关

x264编码
ffmpeg 编码示例
码流控制
h264编解码末尾丢帧

示例

1. 编码前初始化，返回视频宽高
   int* decode_init(char * in_filename)
   {
   avcodec_register_all();
   av_register_all();
   decode_frame = av_frame_alloc();
   AVPacket pkt;
   //获取各种上下文
   if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
   retu = -1;
   goto end;
   }
   if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
   retu = -2;
   goto end;
   }
   //例遍流，找到流所对应得下标
   for (i = 0; i < ifmt_ctx->nb_streams; i++) {
   / /Create output AVStream according to input AVStream
   AVFormatContext *ofmt_ctx;
   AVStream *in_stream = ifmt_ctx->streams[i];
   AVStream *out_stream = NULL;

            if (ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
                videoindex = i;
   
            }
        }
        //open decoder
        video_dec_ctx = ifmt_ctx->streams[videoindex]->codec;
        video_dec = avcodec_find_decoder(video_dec_ctx->codec_id);
        if(avcodec_open2(video_dec_ctx,video_dec,NULL)<0)
        {
            retu = -3;
            goto end;
        }
        double g_height = ifmt_ctx->streams[videoindex]->codec->height;
        double g_width = ifmt_ctx->streams[videoindex]->codec->width;
   
        int* wh = malloc(sizeof(int)*2);
        wh[0] = g_width;
        wh[1] = g_height;
    end: 
        if(retu != 0)
            return NULL;
        else
            return wh;
    }   
   

2. 解码一帧
   AVFrame* decode_next()
   {
   if(decode_frame!=NULL)
   av_frame_unref(decode_frame);
   int ret = 0;
   int got_frame = 0;
   int error_time = 0;
   while(1)
   {
   //Get an AVPacket
   if (av_read_frame(ifmt_ctx, &pkt) < 0)
   {
   av_free_packet(&pkt);
   goto decode_free;
   }
   if (pkt.stream_index == videoindex)
   {
   ret = avcodec_decode_video2(video_dec_ctx,decode_frame, &got_frame, &pkt);
   if(got_frame)
   goto decode_success;
   else
   {
   if(failed_times ++<30)
   continue;
   else
   goto decode_free;
   }
   }
   av_free_packet(&pkt);
   }
   decode_free:
   av_free_packet(&pkt);
   return NULL;

    decode_success:
        return decode_frame;
    }
   

仅仅是在读取packet之后就停止解码会丢帧，参看
所以要在读取packet失败之后接着调用解码，获取剩余的帧。使用一个变量failed_times 记录编码器中存在的帧数。在读取结束之后接着调用failed_times 次avcodec_decode_video2
int failed_times = 0；
int read_packet_failed = 0;
AVFrame* decode_next()
{
if(decode_frame!=NULL;
av_frame_unref(decode_frame);
int ret = 0;
int got_frame = 0;
int error_time = 0;
while(1)
{
if (av_read_frame(ifmt_ctx, &pkt) < 0)
{
read_packet_failed = 1;
av_free_packet(&pkt);
if(failed_times > 0)
{
failed_times--;
goto decode;
}
else
goto decode_free;
}
if (pkt.stream_index == videoindex)
{
decode:
ret = avcodec_decode_video2(video_dec_ctx,decode_frame, &got_frame, &pkt);
if(got_frame)
goto decode_success;
else
{
if(read_packet_failed)
goto decode_free;
else
{
failed_times ++;
continue;
}
else
goto decode_free;
}
}
av_free_packet(&pkt);
}
decode_free:
av_free_packet(&pkt);
return NULL;
decode_success:
return decode_frame;
}

3. 解码完成之后释放
   int decode_release() { avcodec_close(video_dec_ctx); avformat_close_input(&ifmt_ctx); if(decode_frame!=NULL) { av_frame_free(&decode_frame); decode_frame = NULL; } }