[問題] ffmpeg跳格或倒撥
開發平台(Platform): (Ex: VC++, GCC, Linux, ...)
VC++
額外使用到的函數庫(Library Used): (Ex: OpenGL, ...)
FFMpeg
問題(Question)：
想把影片倒撥與順撥
但每次進入10毫秒的迴圈讀取(av_read_fream讀取)
是用av_seek_frame搜影片一倍速時
發現明顯播放速度不對(太慢)
餵入的資料(Input)：
以下是抓取fps、duration的方法。
AVFormatContext *pFormatCtx;
AVCodecContext *pCodecCtx;
int videoStream;
int fps;
int64_t duration;
if( avformat_open_input(&pFormatCtx, fileName.c_str(), NULL, NULL) != 0)
return AVAFRetValue::IO_ERR;
if(avformat_find_stream_info(pFormatCtx, NULL) < 0)
return AVAFRetValue::IO_ERR;
av_dump_format(pFormatCtx, 0, "avi", 0);
videoStream=-1;
for(int i = 0; i < pFormatCtx->nb_streams; i++)
{
if(pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
{
videoStream = i;
break;
}
}
if(videoStream == -1)
return AVAFRetValue::IO_ERR; // Didn
pCodecCtx=pFormatCtx->streams[videoStream]->codec;
pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
if(pCodec==NULL) {
return AVAFRetValue::IO_ERR;
}
if(avcodec_open2(pCodecCtx, pCodec, NULL)<0)
return AVAFRetValue::IO_ERR;
int64_t duration = pFormatCtx->duration/1000000;
fps = pCodecCtx->pkt_timebase.den;
預期的正確結果(Expected Output)：
期望能在撥放時能有正確的撥放速度
錯誤結果(Wrong Output)：
每次用都下av_seek_frame會使得畫面變慢
是否是milliseconds設法錯誤?
程式碼(Code)：(請善用置底文網頁, 記得排版)
if(direction==PlayDirection::FORWARD)
{
if( speed == PlaySpeed::X1)
milliseconds += (1.0/fps*1000);
if( speed == PlaySpeed::X2)
milliseconds += (2.0/(fps*1000));
if( speed == PlaySpeed::X4)
milliseconds += (4.0/(fps*1000));
if( speed == PlaySpeed::X8)
milliseconds += (8.0/fps*1000);
if( speed == PlaySpeed::X16)
milliseconds += (16.0/fps*1000);
if ( milliseconds >= duration*1000 )
{
milliseconds = duration*1000;
}
}
else
{
if( speed == PlaySpeed::X1)
milliseconds -= (1.0/fps);
if( speed == PlaySpeed::X2)
milliseconds -= (2.0/fps);
if( speed == PlaySpeed::X4)
milliseconds -= (4.0/fps);
if( speed == PlaySpeed::X8)
milliseconds -= (8.0/fps);
if( speed == PlaySpeed::X16)
milliseconds -= (16.0/fps);
if( milliseconds <= -duration*1000 )
{
milliseconds = -duration*1000 ;
}
}
av_init_packet(&packet);
packet.data = NULL;
packet.size = 0;
////////////////搜尋影格//////////////////
if(av_seek_frame(pFormatCtx,-1,milliseconds*1000,AVSEEK_FLAG_ANY)<0)
return &packet;
while(av_read_frame(pFormatCtx, &packet)>=0) {
if(packet.stream_index==videoStream) {
return &packet;
}
}
--
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