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• 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

• How to create video with images and different time interval ?

  14 mai 2012, par Preet Sandhu

  I am struggling with this command :

  ffmpeg -loop 1 -r 5 -i img_0.jpg -c:v libx264 -preset slow -tune stillimage -crf 24 -t 20 $frame_target

  it creates 20 sec video with one image. i need to put more images, so i make this like :

  ffmpeg -loop 1 -r 5 -i img_%d.jpg -c:v libx264 -preset slow -tune stillimage -crf 24 -t 20 $frame_target

  but this thing create video of 20 sec but images are changing multiple times. basically i want to divide time interval and every image should show ones only.

• Streaming without Content-Length in response

  29 août 2011, par kain

  I'm using Node.js, Express (and connect), and fluent-ffmpeg.

  We want to stream audio files that are stored on Amazon S3 through http.

  We have all working, except that we would like to add a feature, the on-the-fly conversion of the stream through ffmpeg.

  This is working well, the problem is that some browsers checks in advance before actually getting the file.

  Incoming requests containing the Range header, for which we reply with a 206 with all the info from S3, have a fundamental problem : we need to know in advance the content-length of the file.

  We don't know that since it is going through ffmpeg.

  One solution might be to write out the resulting content-length directly on S3 when storing the file (in a special header), but this means we have to go through the pain of having queues to encode after upload just to know the size for future requests.
  It also means that if we change compressor or preset we have to go through all this over again, so it is not a viable solution.

  We also noticed big differencies in the way Chrome and Safari request the audio tag src, but this may be discussion for another topic.

  Fact is that without a proper content-length header in response everything seems to break or browsers goes in an infinite loop or restart the stream at pleasure.

  Ideas ?