Recherche avancée

Sur d’autres sites (4594)

• RoQ on Dreamcast

  18 mars 2011, par Multimedia Mike — Sega Dreamcast

  I have been working on that challenge to play back video on the Sega Dreamcast. To review, I asserted that the RoQ format would be a good fit for the Sega Dreamcast hardware. The goal was to play 640x480 video at 30 frames/second. Short version : I have determined that it is possible to decode such video in real time. However, I ran into certain data rate caveats.

  First off : Have you ever wondered if the Dreamcast can read an 80mm optical disc ? It can ! I discovered this when I only had 60 MB of RoQ samples to burn on a disc and a spindle full of these 210MB-capacity 80mm CD-Rs that I never have occasion to use.

  
  
  

  New RoQ Library
  There are open source RoQ decoders out there but I decided to write a new one. A few reasons : 1) RoQ is so simple that I didn’t think it would take too long ; 2) it would be nice to have a RoQ library that is license-compatible (BSD-like) with the rest of the KallistiOS distribution ; 3) the idroq.tar.gz distribution, while license-compatible, has enough issues that I didn’t want to correct it.

  Thankfully, I was correct about the task not being too difficult : I put together a new RoQ decoder in short order. I’m a bit embarrassed to admit that the part I had the most trouble with was properly converting YUV -> RGB.
  
  About the approach I took : While the original idroq.tar.gz decoder maintains YUV 4:2:0 codebooks (which led to chroma bugs during motion compensation) and FFmpeg’s decoder maintains YUV 4:4:4 codebooks, this decoder is built to convert the YUV 4:2:0 vectors into RGB565 vectors during the vector unpacking phase. Thus, the entire frame is rendered in RGB565 — no lengthy YUV -> RGB conversion after decoding — and all pixels are shuffled around as 16-bit units (minor speedup vs. shuffling everything as bytes).

  I also entertained the idea of maintaining YUYV codebooks (since the DC supports that colorspace as a texture format). But I scrapped that idea when I remembered it would lead to the same chroma bleeding problem seen in the original idroq.tar.gz decoder.

  Onto The Dreamcast
  I developed the library on a Linux computer, allowing it to output a series of PNM files for visual verification and debugging. Dropping it into a basic DC/KOS-compatible program was trivial and the first order of business was profiling.

  At first, I profiled the entire decode operation : open file, then read and decode each chunk while tossing away the results. I was roundly disappointed to see that, e.g., an 8.5-second RoQ sample needed a little more than 20 seconds to complete. Not real time. I performed a series of optimizations on the decoding library that netted notable performance gains when profiling on Linux. When I brought these same optimizations over to the DC, decoding time didn’t improve at all. This was my first suspicion that perhaps my assumptions regarding the DC’s optical drive’s data rate were not correct.

  Dreamcast Data Rate Profiling
  Let’s start with some definitions : In terms of data rate, an ’X’, i.e., 1X is the minimum data rate needed to read CD quality audio from a disc. At that speed, a drive should be able to stream 75 sectors each second. When reading mode 1/form 1 CD-ROM data, each sector has 2048 bytes (2 kbytes), so a single-speed data rate should achieve 150 kbytes/sec.

  The Dreamcast is supposed to possess a 12X optical drive. This would imply a maximum data rate of 150 kbytes/sec * 12 = 1800 kbytes/sec.

  Rigging up a trivial experiment using the RoQ samples burned on a few different CD-R discs, the best data rate I can see is about 500-525 kbytes/sec, or around 3.5X.

  Where’s the discrepancy ? My first theory has to do with the fact that not all optical media is created equal. This is why optical drives often advertise a slew of numbers which refer to the best theoretical speed for reading a CD vs. writing a CD-R vs. writing a CD-RW, etc. Perhaps the DC drive can’t read CD-Rs very quickly. To test this theory, I tried streaming a large file from a conventionally mastered CD-ROM. This worked well for the closest CD-ROM I had on hand : I was able to stream data at a rate that works out to about 6.5X.

  I smell a science project for another evening : Profiling read speeds from a mastered CD-ROM, burned CD-R, and also a mastered GD-ROM, on each of the 3 Dreamcast consoles I possess (I’ve heard that there’s variance between optical drives depending on manufacturing run).

  The Good News
  I added a little finer-grained code to profile just the video decoding functions. The good news is that the decoder meets my real time goals : That 8.5-second RoQ sample encoded at 640x480x30fps makes its way through the video decoding functions on the DC in a little less than 5 seconds. If the optical drive can supply the data fast enough, the video decoder can take care of the rest.

  The RoQ encoder included with FFmpeg does not honor any bitrate parameters. Instead, I encoded the same file at 320x240. It reportedly decoded in real time and can be streamed in real time as well.

  I say "reportedly" because I’m simply working from textual output at this point ; the next phase is to hook the decoder up to the display hardware.

• Matomo to end support for Internet Explorer 11

  21 septembre 2021, par Matomo Core Team — Community

  A lot of the Matomo user interface is built on top of a programming framework called “Angular.js”. The support for this framework will end very soon, meaning we have to migrate the Matomo user interface to an alternative framework. The Matomo development team has chosen this new framework to be “Vue.js 3”.

  Unfortunately, Vue.js does not support Internet Explorer 11 (IE 11). Therefore, we have to drop the support for IE 11. Many other popular services like Microsoft and WordPress recently did the same. This is happening because IE 11 was released about 8 years ago and is now used by less than 0.5% of the internet. 

  When will this change happen ?

  Our next release (Matomo 4.5) will still support IE 11. It will show a notification in the user interface if you are using Internet Explorer to make you aware of this upcoming change. 

  When Matomo 4.6 is released around November 2021, then IE 11 will no longer be supported.

  What does “end support” mean ?

  The Matomo user interface will work less and less over time for people using IE 11 as a browser. While Matomo 4.6 might still mostly work with IE 11, once we migrate more of the user interface the functionality will stop working completely. It’s possible that even Matomo 4.6 will no longer be functional with IE 11 at all.

  What should I do now ?

  If you are impacted by this, then we strongly recommend that you switch to a more modern browser. Preferably a privacy-friendly browser like Mozilla Firefox or Brave. But any modern browser including Microsoft Edge, Safari and Google Chrome will work just fine.

  If you can’t use a different browser and you are using Matomo On-Premise, then you can install and configure this new plugin which lets you only receive Matomo core updates that are compatible with IE 11. This will prevent you from accidentally upgrading to a Matomo core release that doesn’t work with IE 11, and you can still receive critical security updates and bug fixes until February 2022.

  Will this affect the Matomo JavaScript tracker ?

  No, all visitors using IE 11 will still be tracked and Matomo tracker will support the same browsers as before. Meaning also some older versions of Internet Explorer are still supported.

  Have any questions about this ?

  Get in touch with us 

• The Future of the VP8 Bitstream

  18 juin 2010, par noreply@blogger.com (John Luther) — vp8

  Recently we’ve seen software products such as VLC, FFmpeg, Logitech Vid, Flumotion and Tixeo adopting and using WebM and VP8 (the video codec in WebM) in exciting new ways.

  In addition to software developers, many hardware vendors have committed to shipping VP8-accelerated products based on our current bitstream in 2011 . Devices that use hardware acceleration for video are a very small percentage of overall web traffic today, but they are a rapidly growing segment of the market and our project must be mindful of these vendors’ needs. Given the longer lead times for changes in chipsets, hardware companies implementing the codec today need to be confident that it will be stable and supported as VP8 content proliferates.

  Like every codec, WebM is not immune to change ; the difference in our project is that the improvements are publicly visible, and compatibility and implementation issues can be worked through in an open forum.

  So, to maintain codec stability while also allowing for quality and performance improvements in VP8, we have added an experimental branch to the VP8 source tree. The WebM community can use this unstable branch to propose changes to VP8 that will produce the best video codec possible, but without the constraints of a frozen bitstream. At some point in the future, when the experimental branch proves significantly better than the stable branch, we will create a new version of the codec.

  Teams dedicated to improving WebM are actively investigating and evaluating new techniques, and are committed to do so for the long term. We encourage the WebM community to keep contributing as well. To learn more about the experimental branch and get involved, see our repository layout page.

  Jim Bankoski is Codec Engineering Manager at Google.