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• ffmpeg avformat / avcodec unexpected pts / dts values are written to output when encoding video

  2 août 2022, par ray_ray_ray

  I try to follow the examples for encoding video using ffmpeg C API given in https://ffmpeg.org/doxygen/trunk/transcoding_8c-example.html and https://ffmpeg.org/doxygen/trunk/encode_video_8c-example.html

  


  I put together the following code to do some very simple encoding

  


  void encode(AVFormatContext* fmt_ctx, AVCodecContext* enc_ctx, AVFrame *frame, AVPacket *pkt) {
    int ret = avcodec_send_frame(enc_ctx, frame);

    while (ret >= 0) {
        ret = avcodec_receive_packet(enc_ctx, pkt);
        if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
            return;

        } else if (ret < 0) {
            std::printf("Error during encoding\n");
            exit(1);
        }

        std::printf("pts=%zd dts=%zd\n", pkt->pts, pkt->dts);
        av_interleaved_write_frame(fmt_ctx, pkt);
    }
}

int main() {
    av_log_set_level(AV_LOG_ERROR);

    AVFormatContext* fmt_ctx = nullptr;
    avformat_alloc_output_context2(&fmt_ctx, NULL, NULL, "f:/videoOut.mp4");
    AVStream* videoStream = avformat_new_stream(fmt_ctx, NULL);
    const AVCodec* codec = avcodec_find_encoder(AV_CODEC_ID_H264);
    AVCodecContext* codec_ctx = avcodec_alloc_context3(codec);

    int w = 100;
    int h = 100;
    codec_ctx->width = w;
    codec_ctx->height = h;
    codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;
    codec_ctx->time_base = { 1, 10 };
    codec_ctx->framerate = { 10, 1 };
    codec_ctx->gop_size = 20;
    codec_ctx->max_b_frames = 4;

    avcodec_parameters_from_context(videoStream->codecpar, codec_ctx);
    avio_open(&fmt_ctx->pb, fmt_ctx->url, AVIO_FLAG_WRITE);
    avformat_write_header(fmt_ctx, NULL);

    AVPacket* videoPacket = av_packet_alloc();
    avcodec_open2(codec_ctx, codec, NULL);
    AVFrame* frame = av_frame_alloc();
    frame->format = codec_ctx->pix_fmt;
    frame->width = codec_ctx->width;
    frame->height = codec_ctx->height;

    av_frame_get_buffer(frame, 0);
    av_frame_make_writable(frame);

    for (int i = 0; i < 25; i++) {
        av_frame_make_writable(frame);

        for (int y = 0; y < codec_ctx->height; y++) {
            for (int x = 0; x < codec_ctx->width; x++) {
                frame->data[0][y * frame->linesize[0] + x] = i * 4;
            }
        }
        for (int y = 0; y < codec_ctx->height / 2; y++) {
            for (int x = 0; x < codec_ctx->width / 2; x++) {
                frame->data[1][y * frame->linesize[1] + x] = 20 + i * 2;
                frame->data[2][y * frame->linesize[2] + x] = 20 + i * 2;
            }
        }

        frame->pts = i;
        encode(fmt_ctx, codec_ctx, frame, videoPacket);
    }

    encode(fmt_ctx, codec_ctx, nullptr, videoPacket);
    
    av_write_trailer(fmt_ctx);
    avio_close(fmt_ctx->pb);

    av_packet_free(&videoPacket);
    avcodec_free_context(&codec_ctx);
    av_frame_free(&frame);
    avformat_free_context(fmt_ctx);
}


  


  this will output the following pts and dts values directly before handing over to av_interleaved_write

  


  pts=0 dts=-2
pts=5 dts=-1
pts=2 dts=0
pts=1 dts=1
pts=3 dts=2
pts=4 dts=3
pts=10 dts=4
pts=7 dts=5
pts=6 dts=6
pts=8 dts=7
pts=9 dts=8
pts=15 dts=9
pts=12 dts=10
pts=11 dts=11
pts=13 dts=12
pts=14 dts=13
pts=19 dts=14
pts=17 dts=15
pts=16 dts=16
pts=18 dts=17
pts=20 dts=18
pts=24 dts=19
pts=22 dts=20
pts=21 dts=21
pts=23 dts=22


  


  But when I afterwards examine the written file using the command ffprobe videoOut.mp4 -show_frames > frames.txt those values end up being identical for each frame, starting at pts=0 / pkt_dts=0 for the first frame, increasing for each frame, and the last two frames even end up having pts=23 / pkt_dts=N/A and pts=24 / pkt_dts=N/A respectively.

  


  This seems wrong to me ? These values should not be the same at least for B frames, right ? And there certainly are B frames in the written video. Why are these values reset at all somewhere inside the av_interleaved_write function ? Is there some setting I am missing ?

  


• ffmpeg combining three images into a looped video

  28 juin 2018, par Armand

  So I have three images that I need to combine into a 10 second video, I have searched around and in the end I came up with the following command, it is generating a video but not what I expected.

  ffmpeg.exe -loop 1 -framerate 1 -i 20180627124135055101050.JPG -i 20180627124135056101051.JPG -i 20180627124135057101052.JPG -i 20180627124135056101051.JPG -vf framestep=4,setpts=N/FRAME_RATE/TB -c:v mpeg4 -t 10 video.mp4

  It is currently generating a video of 12 seconds in length, but it is also only showing the first image, I have played around with the framerate option and the framestep option values but all change that I can see is in the length of the video, it never actually shows the images in the order I need them to display. What I basically need as a result is a giff of the 3 images in the order image 1, image 2, image 3, image 2. But as a mp4 of 10 seconds long.

  Any assistance would be greatly appreciated

  EDIT 1

  So I have made some progress, I am now using the following command to get the correct video output, but now I need it to loop so the total video length can be 10 seconds

  ffmpeg -loop 1 -framerate 25 -t 0.25 -i 20180627124135055101050.JPG  -loop 1 -framerate 24 -t 0.25 -i 20180627124135056101051.JPG -loop 1 -framerate 24 -t 0.25 -i 20180627124135057101052.JPG -loop 1 -framerate 24 -t 0.25 -i 20180627124135056101051.JPG -filter_complex "[0][1][2][3]concat=n=4:v=1:a=0"  video.mp4

• Corrupted output video from ffmpeg combining few videos

  22 février 2019, par David

  Ran ffmpeg on Windows 10 to concatanate 4 videos in this sequence :
  introduction.mp4 1.mp4 2.mp4 3.mp4
  to create combined.mp4

  1.mp4 2.mp4 and 3.mp4 were created identically by ffmpeg from a longer video

  When playing combined.mp4 the introduction.mp4 part was OK, but after that the video stopped.
  If I jumped forward got green and other color blank screen

  This was the ffmpeg command to concatenate :

  set parm=-probesize 1000 -analyzeduration 100000000 -fpsprobesize 1000
  
  c:/tools/ffmpeg64/bin/ffmpeg %parm% -loglevel warning -y -strict -2 -f concat -i videoList.txt -c copy combined.mp4 

  This was the videoList.txt file :

  file introduction.mp4
  
  file 1.mp4
  
  file 2.mp4
  
  file 3.mp4

  The input files attributes are not the same

  introduction.mp4 1456x1028 25fps 111knps total 175kbps

  1.mp4 1280x720 29.97fpd 1107kbps total 1233kbps

  OUTPUT : combined.mp4 1456x1028 4.11 fps 1456kbps total 151kbps