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• Revision 33989 : Correction de quelques items de langue et nettoyage d’items inutiles ...

  27 décembre 2009, par eric@… — Log

  Correction de quelques items de langue et nettoyage d’items inutiles (Langonet)

• My crazy linux.conf.au week

  9 février 2012, par silvia

  In January I attended the annual Australian Linux and Open Source conference (LCA). But since I was sick all of January and had a lot to catch up on, I never got around to sharing all the talks that I gave during that time.

  Drupal Down Under

  It started with a talk at Drupal Down Under, which happened the weekend before LCA. I gave a talk titled “HTML5 video specifications” (video, slides).

  I spoke about the video and audio element in HTML5, how to provide fallback content, how to encode content, how to control them from JavaScript, and briefly about Drupal video modules, though the next presentation provided much more insight into those. I explained how to make the HTML5 media elements accessible, including accessible controls, captions, audio descriptions, and the new WebVTT file format. I ran out of time to introduce the last section of my slides which are on WebRTC.

  Linux.conf.au

  On the first day of LCA I gave a talk both in the Multimedia Miniconf and the Browser Miniconf.

  Browser Miniconf

  In the Browser Miniconf I talked about “Web Standardisation – how browser vendors collaborate, or not” (slides). Maybe the most interesting part about this was that I tried out a new slide “deck” tool called impress.js. I’m not yet sure if I like it but it worked well for this talk, in which I explained how the HTML5 spec is authored and who has input.

  I also sat on a panel of browser developers in the Browser Miniconf (more as a standards than as a browser developer, but that’s close enough). We were asked about all kinds of latest developments in HTML5, CSS3, and media standards in the browser.

  Multimedia Miniconf

  In the Multimedia Miniconf I gave a “HTML5 media accessibility update” (slides). I talked about the accessibility problems of Flash, how native HTML5 video players will be better, about accessible video controls, captions, navigation chapters, audio descriptions, and WebVTT. I also provided a demo of how to synchronize multiple video elements using a polyfill for the multitrack API.

  I also provided an update on HTTP adaptive streaming APIs as a lightning talk in the Multimedia Miniconf. I used an extract of the Drupal conference slides for it.

  Main conference

  Finally, and most importantly, Alice Boxhall and myself gave a talk in the main linux.conf.au titled “Developing Accessible Web Apps – how hard can it be ?” (video, slides). I spoke about a process that you can follow to make your Web applications accessible. I’m writing a separate blog post to explain this in more detail. In her part, Alice dug below the surface of browsers to explain how the accessibility markup that Web developers provide is transformed into data structures that are handed to accessibility technologies.

• FFMPEG Generate video clips and concatenate them all

  8 février 2020, par lms702

  I have a bunch of images (.png) and audio files (.wav) that I want to combine and concatenate. For example, if I have a1.wav, i1.png, a2.wav, and i2.png, I want to output a video that is a1.wav overlayed onto i1.png, then (concatenated to a2.wav overlayed onto i2.png.

  Currently, my approach is to save each individual clip and then concatenate them all at the end.

  To save each clip, I use this command (in a loop for all of my clips) :

  ffmpeg -i {imageFile} -i {audioFile} -nostdin -qscale:v 1 -vcodec libx264 -pix_fmt yuv420p {outputFile.mp4}``

  It outputs an mp4 that kind of works - the playback is really buggy but works in full screen.

  My current approach to concatenating has not been at all successful. I create a list of the clip names and put it into filename then call this command :

  ffmpeg -f concat -i {filename} -c copy clips/finalOutput.mp4

  This outputs a pretty jumbled video and this error repeated :

  [mp4 @ 000001cdec110740] Non-monotonous DTS in output stream 0:1; previous: 1045041, current: 604571; changing to 1045042. This may result in incorrect timestamps in the output file.

  So, a few questions.

  What is the best way to go about this process ?

  Should I be saving each clip or is there a better way to do it all in one command ?

  If I do save each clip, is there a better file format I should use ?

  Plz help with the concatenation command.

  Also note that because I am automating this with python I can build arbitrarily large commands, though that might not be ideal.

  I am very new to this and I would really appreciate any help !