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The pirate bay depuis la Belgique
1er avril 2013, par
Mis à jour : Avril 2013
Langue : français
Type : Image
Autres articles (47)
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Websites made with MediaSPIP
2 mai 2011, parThis page lists some websites based on MediaSPIP.
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Les vidéos
21 avril 2011, parComme les documents de type "audio", Mediaspip affiche dans la mesure du possible les vidéos grâce à la balise html5 .
Un des inconvénients de cette balise est qu’elle n’est pas reconnue correctement par certains navigateurs (Internet Explorer pour ne pas le nommer) et que chaque navigateur ne gère en natif que certains formats de vidéos.
Son avantage principal quant à lui est de bénéficier de la prise en charge native de vidéos dans les navigateur et donc de se passer de l’utilisation de Flash et (...) -
Creating farms of unique websites
13 avril 2011, parMediaSPIP platforms can be installed as a farm, with a single "core" hosted on a dedicated server and used by multiple websites.
This allows (among other things) : implementation costs to be shared between several different projects / individuals rapid deployment of multiple unique sites creation of groups of like-minded sites, making it possible to browse media in a more controlled and selective environment than the major "open" (...)
Sur d’autres sites (7626)
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ffmpeg decoding through C-API leads to artefacts when input resolution is 1200x1600. Am I doing something wrong ?
26 février 2023, par AntonioUsing the C-API and FFmpeg 5.1 I have been able to encode h264 videos with libx264 on Android.
Now I wanted to replay them on Linux inside my C++ application. These videos can be played correctly on a browser, or on other players that I tried like mplayer or ffplay from ffmpeg. Also, I can unroll the frames with
ffmpeg -i recording.mp4 -start_number 0 -qscale:v 5 %06d.jpgand the images look alright.

However in my C++ application every now and then, but in a very repeatable way, I get artifacts (like the bright pixels showing up above the monitor). They do not accumulate, even though they are not related to keyframes. So whatever error is going on, it doesn't seem to have an impact on subsequent frames. I use OpenCV to visualize the output, and I am pretty sure the problem is not the conversion to BGR because the artifact is already there if I simply show the y channel (luminance, grayscale).


These artifacts show up in videos that I have recorded with a 1200x1600 resolution. It is to be noted that 1200 is not divisible by 32 so ffmpeg does add some padding, but I am dealing with it and it's not an issue. Videos recorded at 1920x1440 are replayed with no artifacts. Two sample videos can be found here for download.


Here follows the code I am using, on the bottom you can see a picture of my decoded image with the artifact and the same as unrolled by ffmpeg command line. It should be noted that I am working with a custom built version of ffmpeg, out of conan packages, while the unrolling is done with ffmpeg from command line that comes with Ubuntu.


extern "C" {
#include <libavcodec></libavcodec>avcodec.h>
#include <libavformat></libavformat>avformat.h>
}

#include 
#include 
#include 

#include <iostream>
int main(int argc, char** argv) {

 int ret;

 auto pkt = av_packet_alloc();
 if (!pkt) {
 std::cerr << "Failed av_packet_alloc()" << std::endl;
 exit(1);
 }

 AVFormatContext* av_format = avformat_alloc_context();
 ret = avformat_open_input(&av_format, FILE_NAME, nullptr, nullptr);
 if (ret < 0) {
 std::cerr << "Failed avformat_open_input, Error: " << ret << std::endl;
 ///Error codes https://stackoverflow.com/questions/12780931/ffmpeg-exit-status-1094995529
 exit(1);
 }
 av_dump_format(av_format, 0, FILE_NAME, 0);
 auto video_st_number = av_find_best_stream(av_format, AVMEDIA_TYPE_VIDEO, -1, -1, nullptr, 0);
 if (video_st_number < 0) {
 std::cerr << "av_find_best_stream couldn't find video stream" << std::endl;
 exit(1);
 }
 auto video_st = av_format->streams[video_st_number];
 auto codec_id = video_st->codecpar->codec_id;
 std::cout << "Duration " << video_st->duration << std::endl;
 std::cout << "n_frames " << video_st->nb_frames << std::endl;

 auto frame = av_frame_alloc();
 if (!frame) {
 fprintf(stderr, "Could not allocate video frame\n");
 exit(1);
 }

 auto codec = avcodec_find_decoder(codec_id);
 if (!codec) {
 fprintf(stderr, "Codec not found\n");
 exit(1);
 }

 auto c = avcodec_alloc_context3(codec);
 if (!c) {
 fprintf(stderr, "Could not allocate video codec context\n");
 exit(1);
 }


 if ((ret = avcodec_parameters_to_context(c, video_st->codecpar))) {
 fprintf(stderr, "Failed avcodec_parameters_to_context\n");
 exit(1);
 }

 c->pix_fmt = AV_PIX_FMT_YUV420P;///Not really necessary
 c->thread_count = 1;///No impact

 /* open it */
 if (avcodec_open2(c, codec, NULL) < 0) {
 fprintf(stderr, "Could not open codec\n ");
 exit(1);
 }

 std::size_t counter = 0;
 std::size_t n_keyframes = 0;

 while (ret >= 0) {
 ret = av_read_frame(av_format, pkt);
 if (pkt->size == 0) {
 std::cout << "Skipping packet of size zero" << std::endl;
 av_packet_unref(pkt);
 continue;
 }
 while (avcodec_send_packet(c, pkt) != 0) {
 if (avcodec_receive_frame(c, frame) != 0) {
 std::cerr << "Error receiving frame" << std::endl;
 exit(1);
 } else {
 n_keyframes += frame->key_frame;
 std::cout << "Decoded " << ++counter << " frames. Frame No. " << frame->pts / pkt->duration << " "
 << frame->decode_error_flags << " " << frame->key_frame << " " << n_keyframes << " "
 << frame->pkt_dts << std::endl;
 }
 display(frame);
 }
 av_packet_unref(pkt);
 }

 avcodec_send_packet(c, nullptr);
 std::cout << "Flushing decoder" << std::endl;

 while (avcodec_receive_frame(c, frame) == 0) {
 n_keyframes += frame->key_frame;
 std::cout << "Decoded " << ++counter << " frames. Frame No. " << frame->pts << " " << frame->decode_error_flags
 << " " << frame->key_frame << " " << n_keyframes << " " << frame->pkt_dts << std::endl;

 display(frame);
 }

 avcodec_free_context(&c);
 avformat_free_context(av_format);
 av_frame_free(&frame);
 av_packet_free(&pkt);

 return 0;
}
</iostream>




For completeness, this is the
displayfunction, using openCV

void display(const AVFrame* frame) {
 static std::vector yuv_buffer;
 yuv_buffer.resize(frame->linesize[0] * 3 / 2 * frame->width);
 cv::Mat mYUV(frame->height * 3 / 2, frame->width, CV_8UC1, yuv_buffer.data(), frame->linesize[0]);
 memcpy(mYUV.ptr(), frame->data[0], frame->linesize[0] * frame->height);
 //cv::imshow("grayscale", mYUV.rowRange(0, frame->height));
 //cv::imshow("u", cv::Mat(frame->height / 2, frame->width / 2, CV_8UC1, frame->data[1], frame->linesize[1]));
 //cv::imshow("v", cv::Mat(frame->height / 2, frame->width / 2, CV_8UC1, frame->data[2], frame->linesize[2]));

 int dest_row = frame->height;
 for (int j = 0; j < frame->height / 2; j++) {
 memcpy(mYUV.ptr(dest_row), frame->data[1] + frame->linesize[1] * j, frame->width);
 j++;
 memcpy(mYUV.ptr(dest_row) + frame->width / 2, frame->data[1] + frame->linesize[1] * j, frame->width);
 dest_row++;
 }
 for (int j = 0; j < frame->height / 2; j++) {
 memcpy(mYUV.ptr(dest_row), frame->data[2] + frame->linesize[2] * j, frame->width);
 j++;
 memcpy(mYUV.ptr(dest_row) + frame->width / 2, frame->data[2] + frame->linesize[2] * j, frame->width);
 dest_row++;
 }
 cv::Mat mRGB(frame->height, frame->width, CV_8UC3);
 cvtColor(mYUV, mRGB, cv::COLOR_YUV2BGR_I420, 3);
 cv::imshow("Video", mRGB);
 cv::waitKey(0);
}



Note : The
AVFrame->cv::Matconverter is now available in corrected version as answer here.

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Transcoding to a dnxhd .mxf files will change resolution to 1088p, any chance of geting a 1080p file instead ?
27 février 2023, par willjonesvfxExporting to a .mov file will give me a 1920x1080p file as required
However the exact same code exporting to a .mxf will actually export a 1920x1088p file which breaks our pipeline.


ffmpeg - start_number 1000 -i -inputfile%4d.tiff -c:v dnxhd -r 24 -b:v115M -pix_fmt yuv422p outputfile.mxf


Any help would be appreciated !


Thanks
Will


I have tried to set the scale etc and it doesn't change anything. Has anyone ever seen this before and if so is there a fix ? At this point i may report this as a bug !


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why reducing the resolution a percentage doesn't reduce the video the same proportion using ffmpeg ?
14 mars 2023, par user44551I'm using this command :


-y -r -i $inVideoUri -movflags faststart -c:v libx265 -s $videoResolution -c:a copy -preset ultrafast $outPutUri"


However, if "videoResolution" is a 50% of the original video resolution, the resulting file size is not 50% of the original one. I assume there are some headers or metadata added during the process but I would like to know how to estimate the final video size.


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