Recherche avancée

Sur d’autres sites (4964)

• The neutering of Google Code-In 2011

  23 octobre 2011, par Dark Shikari — development, GCI, google, x264

  Posting this from the Google Summer of Code Mentor Summit, at a session about Google Code-In !

  Google Code-In is the most innovative open-source program I’ve ever seen. It provided a way for students who had never done open source — or never even done programming — to get involved in open source work. It made it easy for people who weren’t sure of their ability, who didn’t know whether they could do open source, to get involved and realize that yes, they too could do amazing work — whether code useful to millions of people, documentation to make the code useful, translations to make it accessible, and more. Hundreds of students had a great experience, learned new things, and many stayed around in open source projects afterwards because they enjoyed it so much !

  x264 benefitted greatly from Google Code-In. Most of the high bit depth assembly code was written through GCI — literally man-weeks of work by an professional developer, done by high-schoolers who had never written assembly before ! Furthermore, we got loads of bugs fixed in ffmpeg/libav, a regression test tool, and more. And best of all, we gained a new developer : Daniel Kang, who is now a student at MIT, an x264 and libav developer, and has gotten paid work applying the skills he learned in Google Code-In !

  Some students in GCI complained about the system being “unfair”. Task difficulties were inconsistent and there were many ways to game the system to get lots of points. Some people complained about Daniel — he was completing a staggering number of tasks, so they must be too easy. Yet many of the other students considered these tasks too hard. I mean, I’m asking high school students to write hundreds of lines of complicated assembly code in one of the world’s most complicated instruction sets, and optimize it to meet extremely strict code-review standards ! Of course, there may have been valid complaints about other projects : I did hear from many students talking about gaming the system and finding the easiest, most “profitable” tasks. Though, with the payout capped at $500, the only prize for gaming the system is a high rank on the points list.

  According to people at the session, in an effort to make GCI more “fair”, Google has decided to change the system. There are two big changes they’re making.

  Firstly, Google is requiring projects to submit tasks on only two dates : the start, and the halfway point. But in Google Code-In, we certainly had no idea at the start what types of tasks would be the most popular — or new ideas that came up over time. Often students would come up with ideas for tasks, which we could then add ! A waterfall-style plan-everything-in-advance model does not work for real-world coding. The halfway point addition may solve this somewhat, but this is still going to dramatically reduce the number of ideas that can be proposed as tasks.

  Secondly, Google is requiring projects to submit at least 5 tasks of each category just to apply. Quality assurance, translation, documentation, coding, outreach, training, user interface, and research. For large projects like Gnome, this is easy : they can certainly come up with 5 for each on such a large, general project. But often for a small, focused project, some of these are completely irrelevant. This rules out a huge number of smaller projects that just don’t have relevant work in all these categories. x264 may be saved here : as we work under the Videolan umbrella, we’ll likely be able to fudge enough tasks from Videolan to cover the gaps. But for hundreds of other organizations, they are going to be out of luck. It would make more sense to require, say, 5 out of 8 of the categories, to allow some flexibility, while still encouraging interesting non-coding tasks.

  For example, what’s “user interface” for a software library with a stable API, say, a libc ? Can you make 5 tasks out of it that are actually useful ?

  If x264 applied on its own, could you come up with 5 real, meaningful tasks in each category for it ? It might be possible, but it’d require a lot of stretching.

  How many smaller or more-focused projects do you think are going to give up and not apply because of this ?

  Is GCI supposed to be something for everyone, or just or Gnome, KDE, and other megaprojects ?

• avcodec/mpeg12dec : extract only one type of CC substream

  12 mars 2024, par Marth64

  avcodec/mpeg12dec : extract only one type of CC substream
  In MPEG-2 user data, there can be different types of Closed Captions
  
  formats embedded (A53, SCTE-20, or DVD). The current behavior of the
  
  CC extraction code in the MPEG-2 decoder is to not be aware of
  
  multiple formats if multiple exist, therefore allowing one format
  
  to overwrite the other during the extraction process since the CC
  
  extraction shares one output buffer for the normalized bytes.
  This causes sources that have two CC formats to produce flawed output.
  
  There exist real-world samples which contain both A53 and SCTE-20 captions
  
  in the same MPEG-2 stream, and that manifest this problem. Example of symptom :
  
  THANK YOU (expected) —> THTHANANK K YOYOUU (actual)
  The solution is to pick only the first CC substream observed with valid bytes,
  
  and ignore the other types. Additionally, provide an option for users
  
  to manually "force" a type in the event that this matters for a particular
  
  source.
  Signed-off-by : Marth64 <marth64@proxyid.net>
  

  • [DH] libavcodec/mpeg12dec.c

• Back on the Salty Track

  12 juin 2011, par Multimedia Mike — General

  After I posted about my initial encounter and frustration with Google’s Native Client (NaCl) SDK and took a deep breath, I realized that I achieved an important proof of concept— I successfully played music using the NaCl SDK audio output interface. Then I started taking a closer read through the (C-based set of) header files and realized I might be able to make a go of it after all. I had much better luck this time and managed to create a proper Native Client interface that allows for controlling playback, presenting metadata, and toggling individual voices (a fascinating tool for studying classic game music).

  I haven’t bothered to post the actual plugin because, really, what’s the point ? I started with NaCl SDK 0.3 which requires Chrome 12, which means terribly limited reach, even among Chrome users. At least, that was true when I restarted this little project. Chrome 12 was formally released this past week. Chrome development really does move at breakneck pace.

  Anyway, here is a static screenshot of what the plugin currently looks like :

  
  
  

  Not pretty, but it does the job.

  Dev Journal
  Various notes based on this outing :

  • Portability : I tested my plugin using Chrome 12 on 64-bit Windows, Mac, and Linux. Mac and Linux both work ; Windows does not.
  • Build System : SDK 0.3 is still lacking in its ability to compile .cpp files (instead of .cc files) ; necessary because libgme is C++ using .cpp files. This requires some build system modification.
  • Getting the interfaces : This is where I got tripped up the first time around. get_browser_interface() from their example actually refers to a parameter passed in through the PPP_InitializeModule() function. The SDK’s template generator renames this to get_browser().
  • Debugging : I feel unstoppable once I have a printf() mechanism available to me during development. To that end, console.log() from JavaScript outputs to Chrome’s built-in JavaScript console log while putting printf() statements in the actual NaCl plugin causes the messages to show up in /.xsession-errors on Linux/X.
  • Size Matters : The binaries generated with the NaCl 0.3 SDK are ridiculously huge. The basic "Hello World" example in C compiles to binaries that are 6.7 MB and 7.8 MB for the 32- and 64-bit builds, respectively. This made me apprehensive to build a full version of SaltyGME that contains all the bells and whistles offered by the library. However, all of the GME code compiled into the binary adds very little size. Curiously, the C++ version of "Hello World" only ranges from 1.8-2.0 MB for 32- and 64-bit. Is there some kind of C tax happening here ? Note that running ’strip’ on the resulting .nexe files (they’re ELF files, after all) brings the sizes down into the C++ range, but at the cost of causing them to not work (more specifically, not even load).
  • No Messaging : The NaCl SDK is supposed to have a messaging interface which allows the NaCl plugin to send asynchronous messages up to the hosting page. When I try to instantiate it, I get a NULL. I’m stuck with the alternative of polling from the JavaScript side to, e.g., determine when a song has finished loading via the network.

  That’s all I can think of for now. I may work on this a little more (I’d like to at least see some audio visualization). Maybe Google will enable NaCl per default sometime around Chrome 21 and this program will be ready for prime time by then.

  See Also :

  • My first attempt at this same project