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• How to save h264 frames as jpeg images using ffmpeg ?

  17 août 2020, par Matthew Czarnek

  I would like to save thumbnails from a h264 stream that I'm turning into ffmpeg avpackets as jpegs.

  


  I'm started with a h264 AVPacket (iframe) and decode it into an AVFrame using avcodec_send_packet/avcodec_receive_frame. Now trying to go from AVFrame and convert into AVPacket using avcodec_send_frame/avcodec_receive_packet

  


  I can convert to png instead jpg, though I do get a the video looking like it's outputting three separate frames squeezed side by side into one. Wondering if it's one frame is R, next G, and finally B. I'm not sure, clearly I'm doing something wrong there. I figured it's possible it's the png encoder and I don't need it, so let's get jpg working first. But jpg is outputting unopenable files.

  


  Any advice ?

  


  Here is my code :

  


  int output_thumbnails(AVPacket* video_packet)
{
    char png_file_name[max_chars_per_filename];
    char thumbnail_id_char[10];
    _itoa_s(thumbnail_id, thumbnail_id_char, 10);
    strcpy_s(png_file_name, max_chars_per_filename, time_stamped_filepath);
    strcat_s(png_file_name, max_chars_per_filename, time_stamped_filename);
    strcat_s(png_file_name, max_chars_per_filename, thumbnail_id_char);
    strcat_s(png_file_name, max_chars_per_filename, ".jpg");
    thumbnail_id++;

    int error_code = send_AVPacket_to_videocard(video_packet, av_codec_context_RTSP);

    //if (error_code == AVERROR_EOF)
    //{
    //  //  error_code = videocard_to_PNG(png_file_name, av_codec_context_RTSP, av_codec_RTSP);
    //}
    if (error_code == AVERROR(EAGAIN)) //send packets to videocard until function returns EAGAIN
    {
        error_code = videocard_to_PNG(png_file_name, av_codec_context_RTSP);

        //EAGAIN means that the video card buffer is ready to have the png pulled off of it
        if (error_code == AVERROR_EOF)
        {
            //  error_code = videocard_to_PNG(png_file_name, av_codec_context_RTSP, av_codec_RTSP);
        }
        else if (error_code == AVERROR(EAGAIN))
        {

        }
        else
        {
            deal_with_av_errors(error_code, __LINE__, __FILE__);
        }
    }
    else
    {
        deal_with_av_errors(error_code, __LINE__, __FILE__);
    }
    
    return 0;
}


  


  VideoThumbnailGenerator.h :
#include "VideoThumbnailGenerator.h"

  


  bool decoder_context_created = false;
bool encoder_context_created = false;

AVCodecContext* h264_decoder_codec_ctx;
AVCodecContext* thumbnail_encoder_codec_ctx;

int send_AVPacket_to_videocard(AVPacket* packet, AVCodecContext* codec_ctx)
{
    if(!decoder_context_created)
    {
        AVCodec* h264_codec = avcodec_find_decoder(codec_ctx->codec_id);
        h264_decoder_codec_ctx = avcodec_alloc_context3(h264_codec);

        h264_decoder_codec_ctx->width = codec_ctx->width;
        h264_decoder_codec_ctx->height = codec_ctx->height;
        h264_decoder_codec_ctx->pix_fmt = AV_PIX_FMT_RGB24;
        h264_decoder_codec_ctx->codec_type = AVMEDIA_TYPE_VIDEO;
        h264_decoder_codec_ctx->skip_frame = AVDISCARD_NONINTRA;//AVDISCARD_NONREF;//AVDISCARD_NONINTRA;
        
        h264_decoder_codec_ctx->time_base.num = 1;
        h264_decoder_codec_ctx->time_base.den = 30;

        h264_decoder_codec_ctx->extradata = codec_ctx->extradata;
        h264_decoder_codec_ctx->extradata_size = codec_ctx->extradata_size;
        
        int error_code = avcodec_open2(h264_decoder_codec_ctx, h264_codec, NULL);
        if (!h264_codec) {
            return -1;
        }

        if (error_code < 0)
        {
            return error_code;
        }
        decoder_context_created = true;
    }

    
    //use hardware decoding to decode video frame
    int error_code = avcodec_send_packet(h264_decoder_codec_ctx, packet);
    if(error_code == AVERROR(EAGAIN))
    {
        return AVERROR(EAGAIN);
    }
    if(error_code<0)
    {
        printf("Error: Could not send packet to video card");
        return error_code;
    }

    return 0;
}

int videocard_to_PNG(char *png_file_path, AVCodecContext* codec_ctx)
{
    if (!encoder_context_created)
    {
        //AVCodec* thumbnail_codec = avcodec_find_encoder(AV_CODEC_ID_PNG);
        AVCodec* thumbnail_codec = avcodec_find_encoder(AV_CODEC_ID_JPEG2000);
        thumbnail_encoder_codec_ctx = avcodec_alloc_context3(thumbnail_codec);

        thumbnail_encoder_codec_ctx->width = 128;
        thumbnail_encoder_codec_ctx->height = (int)(((float)codec_ctx->height/(float)codec_ctx->width) * 128);
        thumbnail_encoder_codec_ctx->pix_fmt = AV_PIX_FMT_RGB24; //AV_PIX_FMT_YUVJ420P
        thumbnail_encoder_codec_ctx->codec_type = AVMEDIA_TYPE_VIDEO;

        thumbnail_encoder_codec_ctx->time_base.num = 1;
        thumbnail_encoder_codec_ctx->time_base.den = 30;

        bool thread_check = thumbnail_encoder_codec_ctx->thread_type & FF_THREAD_FRAME;
        bool frame_threads_check = thumbnail_encoder_codec_ctx->codec->capabilities & AV_CODEC_CAP_FRAME_THREADS;
        
        int error_code = avcodec_open2(thumbnail_encoder_codec_ctx, thumbnail_codec, NULL);
        if (!thumbnail_codec) {
            return -1;
        }

        if (error_code < 0)
        {
            return error_code;
        }
        encoder_context_created = true;
    }
    
    AVFrame* thumbnail_frame = av_frame_alloc();
    AVPacket* thumbnail_packet = av_packet_alloc();
    //av_init_packet(png_packet);
    int error_code = avcodec_receive_frame(h264_decoder_codec_ctx, thumbnail_frame);

    //check for errors everytime
    //note EAGAIN errors won't get here since they won't get past while
    if (error_code < 0 && error_code != AVERROR(EAGAIN))
    {
        printf("Error: Could not get frame from video card");
        return error_code;
    }
    //empty buffer if there are any more frames to pull (there shouldn't be)
    //while(error_code != AVERROR(EAGAIN))
    //{
    //  //check for errors everytime
    //  //note EAGAIN errors won't get here since they won't get past while
    //  if (error_code < 0)
    //  {
    //      printf("Error: Could not get frame from video card");
    //      return error_code;
    //  }
    //  
    //  error_code = avcodec_receive_frame(h264_decoder_codec_ctx, png_frame);
    //}

    //now we convert back to AVPacket, this time one holding PNG info, so we can store to file
    error_code = avcodec_send_frame(thumbnail_encoder_codec_ctx, thumbnail_frame);

    if (error_code >= 0) {
        error_code = avcodec_receive_packet(thumbnail_encoder_codec_ctx, thumbnail_packet);

        FILE* out_PNG;

        errno_t err = fopen_s(&out_PNG, png_file_path, "wb");
        if (err == 0) {
            fwrite(thumbnail_packet->data, thumbnail_packet->size, 1, out_PNG);
        }
        fclose(out_PNG);

    }
    return error_code;
}


  


• .bat script : loop over files and save command to variable

  29 septembre 2020, par Rolf vd H

  Gooddday,

  


  I want to shorten a folder of movies to cut the last part of it. To do that I use ffmpeg & ffprobe.
The time to be cut off is 5.52 seconds.
If I want to do that, first I have to get the time of the movie and then (the second command in the loop), I have to subtract the 5.52 seconds.

  


  For now I have the following but I can't get it right :

  


  mkdir outputsss
for %%a in ("FOLDER\*.mp4") do (
 ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 "FOLDER\%%~na.mp4"
 ffmpeg -i "FOLDER\%%~na.mp4" -t 18.6 -c copy output.mp4
)
pause


  


  In the above code example the "ffprobe" calculates the time of the movie.
The "ffmpeg" renders the movie again for 18.6 seconds. But the time should be calculated by subtract 5.52 seconds from the "ffprobe" result.

  


  Can anyone help me please on how to do this ?

  


• FFMPEG / MJPEG Encoding / How to add DQT table in packet data ?

  20 mai 2020, par GoodSimon

  I write my own transcoder in C++ to convert any image to jpeg based on the examples in ffmpeg sources. I use the MJPEG codec to create a jpeg image. By sending AVFrame to the MJPEG encoder I get AVPacket. Then I just take the data from the packet->data structure with the size avpacket->size and save it to a file with the jpg extension.
The problem is that the finished JPEG image has only one DQT (Define Quantization Table). As far as I understand, there should be two tables in the file.

  



  What do I need to do to have 2 quantization tables in avpacket->data ?