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Bug de détection d’ogg
22 mars 2013, par
Mis à jour : Avril 2013
Langue : français
Type : Video
Autres articles (111)
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Multilang : améliorer l’interface pour les blocs multilingues
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Sur d’autres sites (10937)
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Ffmpeg burnt in subtitles out of sync when converting to hls
19 mai 2020, par user1503606I have a file that has subtitles burn into it and they are perfectly in sync.



Here is the file. https://983yqbz442.s3.amazonaws.com/little-mermaid-captions.mp4



I run this command to convert to hls and it creates the .ts files and the .vtt files.



ffmpeg -i little-mermaid-captions.mp4 -profile:v baseline -level 3.0 -s 640x360 -start_number 0 -hls_time 10 -hls_list_size 0 -f hls index.m3u8



I also then create a master.m3u8 file in the same folder with the following.



#EXTM3U
#EXT-X-VERSION:3
#EXT-X-INDEPENDENT-SEGMENTS
#EXT-X-STREAM-INF:BANDWIDTH=800000,RESOLUTION=640x360,SUBTITLES="subtitles"
index.m3u8
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subtitles",NAME="English",DEFAULT=YES,AUTOSELECT=YES,FORCED=NO,LANGUAGE="ENG",URI="index_vtt.m3u8"



Now if I play the master.m3u8 file the subtitles are now out of sync and are about 1 sec to quick. I understand this is probably a setting I am missing through FFmpeg but really stuck on this and would appreciate any insight.



Thanks



More info.



Here is a link to the direct .m3u8 this can be opened in Safari.



https://983yqbz442.s3.amazonaws.com/hlstests/master.m3u8



The generated vtt file is here.



https://983yqbz442.s3.amazonaws.com/hlstests/subs-0.vtt



If you look at the start of the .vtt file you will see this.



WEBVTT

00:06.840 --> 00:10.320
once long ago in the deep blue below



It should start at 00:06.840 but when playing the .m3u8 file in Safari you should see it starts at around 5 seconds not 6 about a second too early.


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dds : Fix palette decoding
21 juillet 2015, par Vittorio Giovara -
How to read RTSP video streams with low latency
24 mai 2023, par rayionI want to make a code to read rtsp video stream with low latency, I just found the libav library to reduce the frame reading and decoding latency, but it still has a latency of about 230ms, can it be faster ?


Here is my code, I don't know why the displayed image is black by running this code :


#include <cstdio>
#include <cstring>
#include <iostream>
#include <sstream>
#include <queue>
#include 
#include <thread>
#include <chrono>
#include <vector>
#include "opencv2/opencv.hpp"
extern "C"
{
#include <libavformat></libavformat>avformat.h>
#include <libavutil></libavutil>error.h>
#include <libavcodec></libavcodec>avcodec.h>
#include <libswscale></libswscale>swscale.h>
}

#define ERR_BUFF_SIZE 1024
bool is_ready = false;
std::mutex mtx;
std::queue frames;
std::chrono::_V2::system_clock::time_point td;
std::vector<avpacket> pkt_queue;

void show()
{
 cv::namedWindow("test");

 while (true)
 {
 if (is_ready == true)
 {
 break;
 }

 if (!frames.empty())
 {

 mtx.lock();
 cv::Mat f = frames.front();
 frames.pop();
 // const auto te = std::chrono::system_clock::now();
 mtx.unlock();
 // int ted = std::chrono::duration_cast(te-td).count();
 // std::cout << "Now show time spent :" <<ted></ted>/ std::cout << "get !"<< std::endl;
 cv::imshow("test", f);
 cv::waitKey(1);
 }
 }

 cv::destroyWindow("test");
}

int main(int argc, char **argv)
{

 const char *url = "rtsp://admin:hik123456@192.168.10.64";

 av_register_all();

 AVFormatContext *container = nullptr;
 AVDictionary *options = NULL;
 av_dict_set(&options, "max_delay", "0", 0);

 av_dict_set(&options, "preset", "ultrafast", 0);

 av_dict_set(&options, "rtsp_transport", "tcp", 0);

 av_dict_set(&options, "tune", "zerolatency", 0);

 if (avformat_open_input(&container, url, NULL, &options) != 0)
 {
 char error_buffer[ERR_BUFF_SIZE];
 av_strerror(errno, error_buffer, sizeof(error_buffer));
 std::cerr << "Failed to open input: " << error_buffer << std::endl;
 return 1;
 }

 if (avformat_find_stream_info(container, NULL) < 0)
 {
 std::cerr << "Failed to find stream info" << std::endl;
 return 1;
 }

 av_dump_format(container, 0, url, 0);

 int video_stream = -1;
 AVCodecParameters *codecContext = nullptr;
 AVCodec *codec = nullptr;
 for (unsigned i = 0; i < container->nb_streams; i++)
 {
 auto codecpar = container->streams[i]->codecpar;
 if (codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
 {
 video_stream = i;
 if (AVCodecID::AV_CODEC_ID_HEVC != codecpar->codec_id)
 std::cout << "now same codec" << std::endl;

 codec = avcodec_find_decoder(codecpar->codec_id);
 codecContext = codecpar;
 break;
 }
 }

 if (!codec)
 {
 std::cerr << "Failed to find codec" << std::endl;
 return 1;
 }

 AVCodecContext *decoderContext = avcodec_alloc_context3(codec);
 int err = avcodec_parameters_to_context(decoderContext, codecContext);
 if (err < 0)
 {
 std::cerr << "Failed to copy codec parameters to decoder context" << std::endl;
 return 1;
 }

 decoderContext->flags2 |= AV_CODEC_FLAG2_FAST;

 if (avcodec_open2(decoderContext, codec, nullptr) < 0)
 {
 std::cerr << "Failed to open codec" << std::endl;
 return 1;
 }

 int i = 0;
 std::thread t(show);

 while (true)
 {
 const auto ta = std::chrono::system_clock::now();
 AVPacket packet;
 av_init_packet(&packet);
 if (av_read_frame(container, &packet) < 0)
 {
 std::cerr << "Failed to read frame" << std::endl;
 return 1;
 }
 const auto tb = std::chrono::system_clock::now();
 int tba = std::chrono::duration_cast(tb - ta).count();
 std::cout << "Now read time spent :" << tba << "us " << std::endl;
 if (packet.stream_index == video_stream)
 {
 AVFrame *frame = av_frame_alloc();
 int got_frame = 0;

 int len = avcodec_decode_video2(decoderContext, frame, &got_frame, &packet);

 const auto tc = std::chrono::system_clock::now();
 int tcb = std::chrono::duration_cast(tc - tb).count();
 std::cout << "Now decode time spent :" << tcb << "us " << std::endl;

 if (len >= 0 && got_frame)
 {
 cv::Mat image(frame->height, frame->width, CV_8UC1, frame->data[0], frame->linesize[0]);
 mtx.lock();
 frames.push(image);
 td = std::chrono::system_clock::now();
 mtx.unlock();
 }
 int tdc = std::chrono::duration_cast(td - tc).count();
 std::cout << "Now get frame time spent :" << tdc << "us " << std::endl;

 av_frame_free(&frame);
 }

 av_packet_unref(&packet);
 i++;
 if (i > 10000)
 {
 is_ready = true;
 break;
 }
 }
 t.join();
 avcodec_close(decoderContext);
 avformat_close_input(&container);

 return 0;
}
</avpacket></vector></chrono></thread></queue></sstream></iostream></cstring></cstdio>

I think this delay is still too slow, but I don't know if there's a better setting.


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