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• How AVCodecContext bitrate, framerate and timebase is used when encoding single frame

  28 mars 2023, par Cyrus

  I am trying to learn FFmpeg from examples as there is a tight schedule. The task is to encode a raw YUV image into JPEG format of the given width and height. I have found examples from ffmpeg official website, which turns out to be quite straight-forward. However there are some fields in AVCodecContext that I thought only makes sense when encoding videos(e.g. bitrate, framerate, timebase, gopsize, max_b_frames etc).

  


  I understand on a high level what those values are when it comes to videos, but do I need to care about those when I just want a single image ? Currently for testing, I am just setting them as dummy values and it seems to work. But I want to make sure that I am not making terrible assumptions that will break in the long run.

  


  EDIT :

  


  Here is the code I got. Most of them are copy and paste from examples, with some changes to replace old APIs with newer ones.

  


  #include "thumbnail.h"
#include "libavcodec/avcodec.h"
#include "libavutil/imgutils.h"
#include 
#include 
#include 

void print_averror(int error_code) {
    char err_msg[100] = {0};
    av_strerror(error_code, err_msg, 100);
    printf("Reason: %s\n", err_msg);
}

ffmpeg_status_t save_yuv_as_jpeg(uint8_t* source_buffer, char* output_thumbnail_filename, int thumbnail_width, int thumbnail_height) {
    const AVCodec* mjpeg_codec = avcodec_find_encoder(AV_CODEC_ID_MJPEG);
    if (!mjpeg_codec) {
        printf("Codec for mjpeg cannot be found.\n");
        return FFMPEG_THUMBNAIL_CODEC_NOT_FOUND;
    }

    AVCodecContext* codec_ctx = avcodec_alloc_context3(mjpeg_codec);
    if (!codec_ctx) {
        printf("Codec context cannot be allocated for the given mjpeg codec.\n");
        return FFMPEG_THUMBNAIL_ALLOC_CONTEXT_FAILED;
    }

    AVPacket* pkt = av_packet_alloc();
    if (!pkt) {
        printf("Thumbnail packet cannot be allocated.\n");
        return FFMPEG_THUMBNAIL_ALLOC_PACKET_FAILED;
    }

    AVFrame* frame = av_frame_alloc();
    if (!frame) {
        printf("Thumbnail frame cannot be allocated.\n");
        return FFMPEG_THUMBNAIL_ALLOC_FRAME_FAILED;
    }

    // The part that I don't understand
    codec_ctx->bit_rate = 400000;
    codec_ctx->width = thumbnail_width;
    codec_ctx->height = thumbnail_height;
    codec_ctx->time_base = (AVRational){1, 25};
    codec_ctx->framerate = (AVRational){1, 25};

    codec_ctx->gop_size = 10;
    codec_ctx->max_b_frames = 1;
    codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;
    int ret = av_image_fill_arrays(frame->data, frame->linesize, source_buffer, AV_PIX_FMT_YUV420P, thumbnail_width, thumbnail_height, 32);
    if (ret < 0) {
        print_averror(ret);
        printf("Pixel format: yuv420p, width: %d, height: %d\n", thumbnail_width, thumbnail_height);
        return FFMPEG_THUMBNAIL_FILL_FRAME_DATA_FAILED;
    }

    ret = avcodec_send_frame(codec_ctx, frame);
    if (ret < 0) {
        print_averror(ret);
        printf("Failed to send frame to encoder.\n");
        return FFMPEG_THUMBNAIL_FILL_SEND_FRAME_FAILED;
    }

    ret = avcodec_receive_packet(codec_ctx, pkt);
    if (ret < 0) {
        print_averror(ret);
        printf("Failed to receive packet from encoder.\n");
        return FFMPEG_THUMBNAIL_FILL_SEND_FRAME_FAILED;
    }

    // store the thumbnail in output
    int fd = open(output_thumbnail_filename, O_CREAT | O_RDWR);
    write(fd, pkt->data, pkt->size);
    close(fd);

    // freeing allocated structs
    avcodec_free_context(&codec_ctx);
    av_frame_free(&frame);
    av_packet_free(&pkt);
    return FFMPEG_SUCCESS;
}


  


• Announcing Long Term Support in Piwik 2 – The analytics platform for your mission critical projects

  11 janvier 2016, par Matthieu Aubry — About, Development

  We are proud to announce our Long Term Support (LTS) for Piwik 2.X !

  Why Long Term Support (LTS) ?

  Part of our mission is to ready Piwik for the enterprise — and ready the enterprise for Piwik. Our fast release cycle and our ability to quickly innovate has served us well for the past seven years and has lead Piwik to being one of the most popular open source projects, used by over one million websites worldwide. But Piwik’s success today has also shown us that this fast release cycle is not suited for all users and customers. Like most large open source projects (such as Ubuntu, Firefox, Debian, Symfony, Node.js, etc.) at Piwik we now also offer a Long Term Support release which gives users the confidence that Piwik can be used for mission critical projects for months to come.

  What does LTS mean for Piwik ?

  For the duration of the LTS period, Piwik 2.X will continue to receive the following fixes :

  • Critical bugs causing data loss or data corruption.
  • Major and Critical security issues.

  Our goal is to offer you a Piwik LTS release that you can trust for all your mission critical projects.

  How long will Piwik 2.X be supported ?

  Piwik 2.X will be supported for at least 12 months after the initial release of Piwik 3.0.0.
  Piwik 3.0.0 is expected to be released in the second half of 2016.
  This means that Piwik 2.X will be supported at least until the second half of 2017.

  Which Piwik version is LTS ?

  The latest Piwik 2.16.X release is our Long Term Support version.

  How do I benefit from the LTS version ?

  To get the full benefits of Piwik LTS, please make sure you are using the latest LTS version. First, update to the latest Piwik 2.X version, then Configure Piwik to use the LTS release channel and then update to the latest LTS version.

  How do I configure Piwik to use the LTS version ?

  By default, Piwik will not use the LTS version. When you use the one-click update your Piwik instance will be updated to the very latest release : when Piwik 3.0.0 will be released, the one click update will update your instance to 3.0.0. It is however possible to configure your Piwik so that you will stay on Piwik 2.X and keep using the LTS Long Term Support version :

  • Login Piwik as the Super User,
  • Go to Settings > General > Update settings,
  • Under “Release channel” click “Latest stable 2.X Long Term Support version”, and click “Save”.
    

  How do I get professional Piwik Support ?

  If you need professional support for your Piwik service get in touch with the Piwik PRO experts.

  ---

  For other questions, feedback or discussion, feel free to join our forums and comment on this LTS forum post.

  We wish you all a fantastic year 2016 !

• Announcing Long Term Support in Piwik 2 – The analytics platform for your mission critical projects

  11 janvier 2016, par Matthieu Aubry — About, Development

  We are proud to announce our Long Term Support (LTS) for Piwik 2.X !

  Why Long Term Support (LTS) ?

  Part of our mission is to ready Piwik for the enterprise — and ready the enterprise for Piwik. Our fast release cycle and our ability to quickly innovate has served us well for the past seven years and has lead Piwik to being one of the most popular open source projects, used by over one million websites worldwide. But Piwik’s success today has also shown us that this fast release cycle is not suited for all users and customers. Like most large open source projects (such as Ubuntu, Firefox, Debian, Symfony, Node.js, etc.) at Piwik we now also offer a Long Term Support release which gives users the confidence that Piwik can be used for mission critical projects for months to come.

  What does LTS mean for Piwik ?

  For the duration of the LTS period, Piwik 2.X will continue to receive the following fixes :

  • Critical bugs causing data loss or data corruption.
  • Major and Critical security issues.

  Our goal is to offer you a Piwik LTS release that you can trust for all your mission critical projects.

  How long will Piwik 2.X be supported ?

  Piwik 2.X will be supported for at least 12 months after the initial release of Piwik 3.0.0.
  Piwik 3.0.0 is expected to be released in the second half of 2016.
  This means that Piwik 2.X will be supported at least until the second half of 2017.

  Which Piwik version is LTS ?

  The latest Piwik 2.16.X release is our Long Term Support version.

  How do I benefit from the LTS version ?

  To get the full benefits of Piwik LTS, please make sure you are using the latest LTS version. First, update to the latest Piwik 2.X version, then Configure Piwik to use the LTS release channel and then update to the latest LTS version.

  How do I configure Piwik to use the LTS version ?

  By default, Piwik will not use the LTS version. When you use the one-click update your Piwik instance will be updated to the very latest release : when Piwik 3.0.0 will be released, the one click update will update your instance to 3.0.0. It is however possible to configure your Piwik so that you will stay on Piwik 2.X and keep using the LTS Long Term Support version :

  • Login Piwik as the Super User,
  • Go to Settings > General > Update settings,
  • Under “Release channel” click “Latest stable 2.X Long Term Support version”, and click “Save”.
    

  How do I get professional Piwik Support ?

  If you need professional support for your Piwik service get in touch with the Piwik experts.

  ---

  For other questions, feedback or discussion, feel free to join our forums and comment on this LTS forum post.

  We wish you all a fantastic year 2016 !