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Médias (1)
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La conservation du net art au musée. Les stratégies à l’œuvre
26 mai 2011
Mis à jour : Juillet 2013
Langue : français
Type : Texte
Autres articles (30)
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Websites made with MediaSPIP
2 mai 2011, parThis page lists some websites based on MediaSPIP.
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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" (...) -
Other interesting software
13 avril 2011, parWe don’t claim to be the only ones doing what we do ... and especially not to assert claims to be the best either ... What we do, we just try to do it well and getting better ...
The following list represents softwares that tend to be more or less as MediaSPIP or that MediaSPIP tries more or less to do the same, whatever ...
We don’t know them, we didn’t try them, but you can take a peek.
Videopress
Website : http://videopress.com/
License : GNU/GPL v2
Source code : (...)
Sur d’autres sites (7432)
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avutil/log : check that len is within the buffer before reading it
27 novembre 2013, par Michael Niedermayer -
Revision 1b556e1f9a : vp9_spatial_svc_encoder : Enable aq-mode for real-time mode. For real-time mode
27 août 2015, par MarcoChanged Paths :
Modify /examples/vp9_spatial_svc_encoder.c
vp9_spatial_svc_encoder : Enable aq-mode for real-time mode.For real-time mode (speeds >=5) enable aq-mode=3.
Change-Id : Ib8b4ef7609bc30ac935742c8d27e8cd89933c6af
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Why android video player that based on ffmpeg can't sync video' time and audio's time ?
6 juillet 2021, par ZSpirytusBackground


Recently, I use ffmpeg to write my first Android video player. But video channel's time is faster than audio channel's time about 2 3 times.


Question


Why android video player audio and video is out of sync ? Video is about faster than audio 2 3 times. Thanks for your reading and answers.


Code


In short, I use PacketDispatcher to read AVPacket from http hlv source :


void PacketDispatcher::RealDispatch() {
 while (GetStatus() != DISPATCHER_STOP) {
 ...

 AVPacket *av_packet = av_packet_alloc();
 int ret = av_read_frame(av_format_context, av_packet);

 // PacketDispatcher is who read the AVPacket from http hlv source 
 // and dispatch to decoder by its stream index.
 decoder_map[av_packet->stream_index]->Push(av_packet);
 }
}


And then, Decoder written by Producer-Consumer Pattern, Decoder maintain a queue that store all the AVPacket received from PacketDispatcher. The code like this :


// write to the queue
void BaseDecoder::Push(AVPacket *av_packet) {
 ...
 av_packet_queue.push(av_packet);
 ...
}

// real decode logic
void BaseDecoder::RealDecode() {
 ...
 while (true) {
 // read frame from codec
 AVFrame *av_frame = av_frame_alloc();
 ret = avcodec_receive_frame(av_codec_ctx, av_frame);

 void *decode_result = DecodeFrame(av_frame);
 // send to render
 m_render->Render(decode_result);
 }
}


And then, I do rendering logic in Render. Render also written by Producer-Consumer Pattern, it maintain a queue that store AVFrame received from Decoder, the code like this :


// write AVFrame
void BaseRender::Render(void *frame_data) {
 ...
 frame_queue.push(frame_data);
 ...
}

// render to surface or Open SL
void BaseRender::RealRender() {
 if (m_render_synchronizer && m_render_synchronizer->Sync(frame_data)) {
 continue;
 }
}


Finally, the synchronizer will decide to sleep time or drop video frame according to the frame pts, frame pts is :


frame_data->pts = av_frame->best_effort_timestamp * av_q2d(GetTimeBase());


Also, video extra delay is :


frame_data->video_extra_delay = av_frame->repeat_pict * 1.0 / fps * 2.0;


RenderSynchronizer code like this :


bool RenderSynchronizer::Sync(void *frame_data) {
 auto base_frame_data = static_cast<baseframedata>(frame_data);
 if (base_frame_data->media_type == AVMEDIA_TYPE_AUDIO) {
 audio_pts = pcm_data->pts;
 return false;
 } else if (base_frame_data->media_type == AVMEDIA_TYPE_VIDEO) {
 video_pts = rgba_data->pts;
 return ReceiveVideoFrame(static_cast<rgbadata>(frame_data));
 }
 return false;
}

bool RenderSynchronizer::ReceiveVideoFrame(RGBAData *rgba_data) {
 if (audio_pts <= 0 || video_pts <= 0) {
 return false;
 }

 double diff = video_pts - audio_pts;
 if (diff > 0) {
 if (diff > 1) {
 av_usleep((unsigned int) (rgba_data->extra_delay * 1000000.0));
 } else {
 av_usleep((unsigned int) ((diff + rgba_data->extra_delay) * 1000000.0));
 }
 return false;
 } else if (diff < 0) {
 LOGD(TAG, "drop video frame");
 return true;
 } else {
 return false;
 }
}
</rgbadata></baseframedata>

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