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• Downscale and padding with FFmpeg

  26 juin 2022, par nrofis

  I have an input video with a resolution of 3000x2160. I want to downscale it to 1920x1080 but keep the aspect ratio and center the original view by adding padding.

  


  I tried this command :

  


  ffmpeg -i input.mkv -c:v libx264 -vf scale=-1:1080,pad=1920:1080:'(ow-iw)/2':0 output.1080.mp4


  


  But I get an error :

  


  


  Padded dimensions cannot be smaller than input dimensions.

  


  


  Of course, since I want to add padding relatively to the output video size.

  


  How can I downscale and add padding to the output view ?

  


• screenrecorder appliaction. video output size issues [closed]

  25 juin 2022, par jNc

  Having working github project
https://github.com/abdullahfarwees/screen-recorder-ffmpeg-cpp

  


  All works perfectly fine, but output video resolution is not correct
I need to change output video resolution

  


  Using ubuntu/gcc/opencv/

  


  [...]
outAVCodecContext->bit_rate = 400000; // 2500000
outAVCodecContext->width = 1920; // <- change this one
outAVCodecContext->height = 1080; // <- and also this one
outAVCodecContext->gop_size = 3;
[...]


  


• Screenrecorder application output video resolution issues [closed]

  23 juin 2022, par JessieK

  Using Github code for ScreenRecorder on Linux
Everything works fine, besides the resolution of output video.
Tried to play with setting, quality has significantly improved, but still no way to change resolution.
I need to get output video with the same size as input video

  


  using namespace std;

    /* initialize the resources*/
    ScreenRecorder::ScreenRecorder()
    {
    
        av_register_all();
        avcodec_register_all();
        avdevice_register_all();
        cout<<"\nall required functions are registered successfully";
    }
    
    /* uninitialize the resources */
    ScreenRecorder::~ScreenRecorder()
    {
    
        avformat_close_input(&pAVFormatContext);
        if( !pAVFormatContext )
        {
            cout<<"\nfile closed sucessfully";
        }
        else
        {
            cout<<"\nunable to close the file";
            exit(1);
        }
    
        avformat_free_context(pAVFormatContext);
        if( !pAVFormatContext )
        {
            cout<<"\navformat free successfully";
        }
        else
        {
            cout<<"\nunable to free avformat context";
            exit(1);
        }
    
    }
    
    /* function to capture and store data in frames by allocating required memory and auto deallocating the memory.   */
    int ScreenRecorder::CaptureVideoFrames()
    {
        int flag;
        int frameFinished;//when you decode a single packet, you still don't have information enough to have a frame [depending on the type of codec, some of them //you do], when you decode a GROUP of packets that represents a frame, then you have a picture! that's why frameFinished will let //you know you decoded enough to have a frame.
    
        int frame_index = 0;
        value = 0;
    
        pAVPacket = (AVPacket *)av_malloc(sizeof(AVPacket));
        av_init_packet(pAVPacket);
    
        pAVFrame = av_frame_alloc();
        if( !pAVFrame )
        {
         cout<<"\nunable to release the avframe resources";
         exit(1);
        }
    
        outFrame = av_frame_alloc();//Allocate an AVFrame and set its fields to default values.
        if( !outFrame )
        {
         cout<<"\nunable to release the avframe resources for outframe";
         exit(1);
        }
    
        int video_outbuf_size;
        int nbytes = av_image_get_buffer_size(outAVCodecContext->pix_fmt,outAVCodecContext->width,outAVCodecContext->height,32);
        uint8_t *video_outbuf = (uint8_t*)av_malloc(nbytes);
        if( video_outbuf == NULL )
        {
            cout<<"\nunable to allocate memory";
            exit(1);
        }
    
        // Setup the data pointers and linesizes based on the specified image parameters and the provided array.
        value = av_image_fill_arrays( outFrame->data, outFrame->linesize, video_outbuf , AV_PIX_FMT_YUV420P, outAVCodecContext->width,outAVCodecContext->height,1 ); // returns : the size in bytes required for src
        if(value < 0)
        {
            cout<<"\nerror in filling image array";
        }
    
        SwsContext* swsCtx_ ;
    
        // Allocate and return swsContext.
        // a pointer to an allocated context, or NULL in case of error
        // Deprecated : Use sws_getCachedContext() instead.
        swsCtx_ = sws_getContext(pAVCodecContext->width,
                            pAVCodecContext->height,
                            pAVCodecContext->pix_fmt,
                            outAVCodecContext->width,
                    outAVCodecContext->height,
                            outAVCodecContext->pix_fmt,
                            SWS_BICUBIC, NULL, NULL, NULL);
    
    
    int ii = 0;
    int no_frames = 100;
    cout<<"\nenter No. of frames to capture : ";
    cin>>no_frames;
    
        AVPacket outPacket;
        int j = 0;
    
        int got_picture;
    
        while( av_read_frame( pAVFormatContext , pAVPacket ) >= 0 )
        {
        if( ii++ == no_frames )break;
            if(pAVPacket->stream_index == VideoStreamIndx)
            {
                value = avcodec_decode_video2( pAVCodecContext , pAVFrame , &frameFinished , pAVPacket );
                if( value < 0)
                {
                    cout<<"unable to decode video";
                }
    
                if(frameFinished)// Frame successfully decoded :)
                {
                    sws_scale(swsCtx_, pAVFrame->data, pAVFrame->linesize,0, pAVCodecContext->height, outFrame->data,outFrame->linesize);
                    av_init_packet(&outPacket);
                    outPacket.data = NULL;    // packet data will be allocated by the encoder
                    outPacket.size = 0;
    
                    avcodec_encode_video2(outAVCodecContext , &outPacket ,outFrame , &got_picture);
    
                    if(got_picture)
                    {
                        if(outPacket.pts != AV_NOPTS_VALUE)
                            outPacket.pts = av_rescale_q(outPacket.pts, video_st->codec->time_base, video_st->time_base);
                        if(outPacket.dts != AV_NOPTS_VALUE)
                            outPacket.dts = av_rescale_q(outPacket.dts, video_st->codec->time_base, video_st->time_base);
                    
                        printf("Write frame %3d (size= %2d)\n", j++, outPacket.size/1000);
                        if(av_write_frame(outAVFormatContext , &outPacket) != 0)
                        {
                            cout<<"\nerror in writing video frame";
                        }
    
                    av_packet_unref(&outPacket);
                    } // got_picture
    
                av_packet_unref(&outPacket);
                } // frameFinished
    
            }
        }// End of while-loop


  


  One part of two parts is above...Actually original app seem to record video of same size as does my application, but still it has not any use

  


  ---

  


  Second part of the code

  


  av_free(video_outbuf);

}

/* establishing the connection between camera or screen through its respective folder */
int ScreenRecorder::openCamera()
{

    value = 0;
    options = NULL;
    pAVFormatContext = NULL;

    pAVFormatContext = avformat_alloc_context();//Allocate an AVFormatContext.
/*

X11 video input device.
To enable this input device during configuration you need libxcb installed on your system. It will be automatically detected during configuration.
This device allows one to capture a region of an X11 display. 
refer : https://www.ffmpeg.org/ffmpeg-devices.html#x11grab
*/
    /* current below is for screen recording. to connect with camera use v4l2 as a input parameter for av_find_input_format */ 
    pAVInputFormat = av_find_input_format("x11grab");
    value = avformat_open_input(&pAVFormatContext, ":0.0+10,250", pAVInputFormat, NULL);
    if(value != 0)
    {
       cout<<"\nerror in opening input device";
       exit(1);
    }

    /* set frame per second */
    value = av_dict_set( &options,"framerate","30",0 );
    if(value < 0)
    {
      cout<<"\nerror in setting dictionary value";
       exit(1);
    }

    value = av_dict_set( &options, "preset", "medium", 0 );
    if(value < 0)
    {
      cout<<"\nerror in setting preset values";
      exit(1);
    }

//  value = avformat_find_stream_info(pAVFormatContext,NULL);
    if(value < 0)
    {
      cout<<"\nunable to find the stream information";
      exit(1);
    }

    VideoStreamIndx = -1;

    /* find the first video stream index . Also there is an API available to do the below operations */
    for(int i = 0; i < pAVFormatContext->nb_streams; i++ ) // find video stream posistion/index.
    {
      if( pAVFormatContext->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO )
      {
         VideoStreamIndx = i;
         break;
      }

    } 

    if( VideoStreamIndx == -1)
    {
      cout<<"\nunable to find the video stream index. (-1)";
      exit(1);
    }

    // assign pAVFormatContext to VideoStreamIndx
    pAVCodecContext = pAVFormatContext->streams[VideoStreamIndx]->codec;

    pAVCodec = avcodec_find_decoder(pAVCodecContext->codec_id);
    if( pAVCodec == NULL )
    {
      cout<<"\nunable to find the decoder";
      exit(1);
    }

    value = avcodec_open2(pAVCodecContext , pAVCodec , NULL);//Initialize the AVCodecContext to use the given AVCodec.
    if( value < 0 )
    {
      cout<<"\nunable to open the av codec";
      exit(1);
    }
}

/* initialize the video output file and its properties  */
int ScreenRecorder::init_outputfile()
{
    outAVFormatContext = NULL;
    value = 0;
    output_file = "../media/output.mp4";

    avformat_alloc_output_context2(&outAVFormatContext, NULL, NULL, output_file);
    if (!outAVFormatContext)
    {
        cout<<"\nerror in allocating av format output context";
        exit(1);
    }

/* Returns the output format in the list of registered output formats which best matches the provided parameters, or returns NULL if there is no match. */
    output_format = av_guess_format(NULL, output_file ,NULL);
    if( !output_format )
    {
     cout<<"\nerror in guessing the video format. try with correct format";
     exit(1);
    }

    video_st = avformat_new_stream(outAVFormatContext ,NULL);
    if( !video_st )
    {
        cout<<"\nerror in creating a av format new stream";
        exit(1);
    }

    outAVCodecContext = avcodec_alloc_context3(outAVCodec);
    if( !outAVCodecContext )
    {
        cout<<"\nerror in allocating the codec contexts";
        exit(1);
    }

    /* set property of the video file */
    outAVCodecContext = video_st->codec;
    outAVCodecContext->codec_id = AV_CODEC_ID_MPEG4;// AV_CODEC_ID_MPEG4; // AV_CODEC_ID_H264 // AV_CODEC_ID_MPEG1VIDEO
    outAVCodecContext->codec_type = AVMEDIA_TYPE_VIDEO;
    outAVCodecContext->pix_fmt  = AV_PIX_FMT_YUV420P;
    outAVCodecContext->bit_rate = 2500000; // 2500000
    outAVCodecContext->width = 1920;
    outAVCodecContext->height = 1080;
    outAVCodecContext->gop_size = 3;
    outAVCodecContext->max_b_frames = 2;
    outAVCodecContext->time_base.num = 1;
    outAVCodecContext->time_base.den = 30; // 15fps

    {
     av_opt_set(outAVCodecContext->priv_data, "preset", "slow", 0);
    }

    outAVCodec = avcodec_find_encoder(AV_CODEC_ID_MPEG4);
    if( !outAVCodec )
    {
     cout<<"\nerror in finding the av codecs. try again with correct codec";
    exit(1);
    }

    /* Some container formats (like MP4) require global headers to be present
       Mark the encoder so that it behaves accordingly. */

    if ( outAVFormatContext->oformat->flags & AVFMT_GLOBALHEADER)
    {
        outAVCodecContext->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    }

    value = avcodec_open2(outAVCodecContext, outAVCodec, NULL);
    if( value < 0)
    {
        cout<<"\nerror in opening the avcodec";
        exit(1);
    }

    /* create empty video file */
    if ( !(outAVFormatContext->flags & AVFMT_NOFILE) )
    {
     if( avio_open2(&outAVFormatContext->pb , output_file , AVIO_FLAG_WRITE ,NULL, NULL) < 0 )
     {
      cout<<"\nerror in creating the video file";
      exit(1);
     }
    }

    if(!outAVFormatContext->nb_streams)
    {
        cout<<"\noutput file dose not contain any stream";
        exit(1);
    }

    /* imp: mp4 container or some advanced container file required header information*/
    value = avformat_write_header(outAVFormatContext , &options);
    if(value < 0)
    {
        cout<<"\nerror in writing the header context";
        exit(1);
    }


    cout<<"\n\nOutput file information :\n\n";
    av_dump_format(outAVFormatContext , 0 ,output_file ,1);


  


  Github link https://github.com/abdullahfarwees/screen-recorder-ffmpeg-cpp