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Des sites réalisés avec MediaSPIP
2 mai 2011, parCette page présente quelques-uns des sites fonctionnant sous MediaSPIP.
Vous pouvez bien entendu ajouter le votre grâce au formulaire en bas de page. -
Support audio et vidéo HTML5
10 avril 2011MediaSPIP utilise les balises HTML5 video et audio pour la lecture de documents multimedia en profitant des dernières innovations du W3C supportées par les navigateurs modernes.
Pour les navigateurs plus anciens, le lecteur flash Flowplayer est utilisé.
Le lecteur HTML5 utilisé a été spécifiquement créé pour MediaSPIP : il est complètement modifiable graphiquement pour correspondre à un thème choisi.
Ces technologies permettent de distribuer vidéo et son à la fois sur des ordinateurs conventionnels (...) -
De l’upload à la vidéo finale [version standalone]
31 janvier 2010, parLe chemin d’un document audio ou vidéo dans SPIPMotion est divisé en trois étapes distinctes.
Upload et récupération d’informations de la vidéo source
Dans un premier temps, il est nécessaire de créer un article SPIP et de lui joindre le document vidéo "source".
Au moment où ce document est joint à l’article, deux actions supplémentaires au comportement normal sont exécutées : La récupération des informations techniques des flux audio et video du fichier ; La génération d’une vignette : extraction d’une (...)
Sur d’autres sites (4241)
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avcodec/aaccoder : Add minimal bias in search_for_ms()
31 mai 2021, par Michael Niedermayer -
avcodec/videotoolbox : Fix undefined symbol with minimal configuration
4 janvier 2022, par Limin Wangavcodec/videotoolbox : Fix undefined symbol with minimal configuration
Please reproduced with the following minimal configure command :
./configure —enable-shared —disable-all —enable-avcodec —enable-decoder=h264 —enable-hwaccel=h264_videotoolboxYou'll get below error :
Undefined symbols for architecture x86_64 :
"_ff_videotoolbox_vpcc_extradata_create", referenced from :
_videotoolbox_start in videotoolbox.o
ld : symbol(s) not found for architecture x86_64
clang : error : linker command failed with exit code 1 (use -v to see invocation)Reported-by : Cameron Gutman <aicommander@gmail.com>
Tested-by : Cameron Gutman <aicommander@gmail.com>
Signed-off-by : Limin Wang <lance.lmwang@gmail.com> -
Why is ffmpeg faster than this minimal example ?
23 juillet 2022, par Dave CeddiaI'm wanting to read the audio out of a video file as fast as possible, using the libav libraries. It's all working fine, but it seems like it could be faster.


To get a performance baseline, I ran this ffmpeg command and timed it :


time ffmpeg -threads 1 -i file -map 0:a:0 -f null -


On a test file (a 2.5gb 2hr .MOV with pcm_s16be audio) this comes out to about 1.35 seconds on my M1 Macbook Pro.


On the other hand, this minimal C code (based on FFmpeg's "Demuxing and decoding" example) is consistently around 0.3 seconds slower.


#include <libavcodec></libavcodec>avcodec.h>
#include <libavformat></libavformat>avformat.h>

static int decode_packet(AVCodecContext *dec, const AVPacket *pkt, AVFrame *frame)
{
 int ret = 0;

 // submit the packet to the decoder
 ret = avcodec_send_packet(dec, pkt);

 // get all the available frames from the decoder
 while (ret >= 0) {
 ret = avcodec_receive_frame(dec, frame);
 av_frame_unref(frame);
 }

 return 0;
}

int main (int argc, char **argv)
{
 int ret = 0;
 AVFormatContext *fmt_ctx = NULL;
 AVCodecContext *dec_ctx = NULL;
 AVFrame *frame = NULL;
 AVPacket *pkt = NULL;

 if (argc != 3) {
 exit(1);
 }

 int stream_idx = atoi(argv[2]);

 /* open input file, and allocate format context */
 avformat_open_input(&fmt_ctx, argv[1], NULL, NULL);

 /* get the stream */
 AVStream *st = fmt_ctx->streams[stream_idx];

 /* find a decoder for the stream */
 AVCodec *dec = avcodec_find_decoder(st->codecpar->codec_id);

 /* allocate a codec context for the decoder */
 dec_ctx = avcodec_alloc_context3(dec);

 /* copy codec parameters from input stream to output codec context */
 avcodec_parameters_to_context(dec_ctx, st->codecpar);

 /* init the decoder */
 avcodec_open2(dec_ctx, dec, NULL);

 /* allocate frame and packet structs */
 frame = av_frame_alloc();
 pkt = av_packet_alloc();

 /* read frames from the specified stream */
 while (av_read_frame(fmt_ctx, pkt) >= 0) {
 if (pkt->stream_index == stream_idx)
 ret = decode_packet(dec_ctx, pkt, frame);

 av_packet_unref(pkt);
 if (ret < 0)
 break;
 }

 /* flush the decoders */
 decode_packet(dec_ctx, NULL, frame);

 return ret < 0;
}


I tried measuring parts of this program to see if it was spending a lot of time in the setup, but it's not – at least 1.5 seconds of the runtime is the loop where it's reading frames.


So I took some flamegraph recordings (using cargo-flamegraph) and ran each a few times to make sure the timing was consistent. There's probably some overhead since both were consistently higher than running normally, but they still have the 0.3 second delta.


# 1.812 total
time sudo flamegraph ./minimal file 1

# 1.542 total
time sudo flamegraph ffmpeg -threads 1 -i file -map 0:a:0 -f null - 2>&1


Here are the flamegraphs stacked up, scaled so that the faster one is only 85% as wide as the slower one. (click for larger)




The interesting thing that stands out to me is how long is spent on
readin the minimal example vs. ffmpeg :



The time spent on
lseekis also a lot longer in the minimal program – it's plainly visible in that flamegraph, but in the ffmpeg flamegraph,lseekis a single pixel wide.

What's causing this discrepancy ? Is ffmpeg actually doing less work than I think it is here ? Is the minimal code doing something naive ? Is there some buffering or other I/O optimizations that ffmpeg has enabled ?


How can I shave 0.3 seconds off of the minimal example's runtime ?


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