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• How to learn audio/video processing ?

  19 mai 2012, par WinOrWin

  I have given some tries using products like Xuggler and Wowza, but I cannot understand how to use them after a while - because I have absolutely no idea over things like "what is sampling" or "what are timestamps and timebases".

  Can I get some help to move from a newbie -> intermediate level, maybe some good links. I am open to read any recommended book. My eventual target is to process/transform media the way I want using ffmpeg or Xuggler.

  Thanks !

• Resurrecting SCD

  6 août 2010, par Multimedia Mike — Reverse Engineering

  When I became interested in reverse engineering all the way back in 2000, the first Win32 disassembler I stumbled across was simply called "Win32 Program Disassembler" authored by one Sang Cho. I took to calling it ’scd’ for Sang Cho’s Disassembler. The original program versions and source code are still available for download. I remember being able to compile v0.23 of the source code with gcc under Unix ; 0.25 is no go due to extensive reliance on the Win32 development environment.

  I recently wanted to use scd again but had some trouble compiling. As was the case the first time I tried compiling the source code a decade ago, it’s necessary to transform line endings from DOS -> Unix using ’dos2unix’ (I see that this has been renamed to/replaced by ’fromdos’ on Ubuntu).

  Beyond this, it seems that there are some C constructs that used to be valid but are now rejected by gcc. The first looks like this :

  PLAIN TEXT

  C :

  1. return (int) c = *(PBYTE)((int)lpFile + vCodeOffset) ;

  Ahem, "error : lvalue required as left operand of assignment". Removing the "(int)" before the ’c’ makes the problem go away. It’s a strange way to write a return statement in general. However, ’c’ is a global variable that is apparently part of some YACC/BISON-type output.

  The second issue is when a case-switch block has a default label but with no code inside. Current gcc doesn’t like that. It’s necessary to at least provide a break statement after the default label.

  Finally, the program turns out to not be 64-bit safe. It is necessary to compile it in 32-bit mode (compile and link with the ’-m32’ flag or build on a 32-bit system). The static 32-bit binary should run fine under a 64-bit kernel.

  Alternatively : What are some other Win32 disassemblers that work under Linux ?

• Announcing the first free software Blu-ray encoder

  25 avril 2010, par Dark Shikari — blu-ray, x264

  For many years it has been possible to make your own DVDs with free software tools. Over the course of the past decade, DVD creation evolved from the exclusive domain of the media publishing companies to something basically anyone could do on their home computer.

  But Blu-ray has yet to get that treatment. Despite the “format war” between Blu-ray and HD DVD ending over two years ago, free software has lagged behind. “Professional” tools for Blu-ray video encoding can cost as much as $100,000 and are often utter garbage. Here are two actual screenshots from real Blu-rays : I wish I was making this up.

  But today, things change. Today we take the first step towards a free software Blu-ray creation toolkit.

  Thanks to tireless work by Kieran Kunyha, Alex Giladi, Lamont Alston, and the Doom9 crowd, x264 can now produce Blu-ray-compliant video. Extra special thanks to The Criterion Collection for sponsoring the final compliance test to confirm x264′s Blu-ray compliance.

  With x264′s powerful compression, as demonstrated by the incredibly popular BD-Rebuilder Blu-ray backup software, it’s quite possible to author Blu-ray disks on DVD9s (dual-layer DVDs) or even DVD5s (single-layer DVDs) with a reasonable level of quality. With a free software encoder and less need for an expensive Blu-ray burner, we are one step closer to putting HD optical media creation in the hands of the everyday user.

  To celebrate this achievement, we are making available for download a demo Blu-ray encoded with x264, containing entirely free content !

  On this Blu-ray are the Open Movie Project films Big Buck Bunny and Elephant’s Dream, available under a Creative Commons license. Additionally, Microsoft has graciously provided about 6 minutes of lossless HD video and audio (from part of a documentary project) under a very liberal license. This footage rounds out the Blu-ray by adding some difficult live-action content in addition to the relatively compressible CGI footage from the Open Movie Project. Finally, we used this sound sample, available under a Creative Commons license.

  You may notice that the Blu-ray image is only just over 2GB. This is intentional ; we have encoded all the content on the disk at appropriate bitrates to be playable from an ordinary 4.7GB DVD. This should make it far easier to burn a copy of the Blu-ray, since Blu-ray burners and writable media are still relatively rare. Most Blu-ray players will treat a DVD containing Blu-ray data as a normal Blu-ray disc. A few, such as the Playstation 3, will not, but you can still play it as a data disc.

  Finally, note that (in accordance with the Blu-ray spec) the disc image file uses the UDF 2.5 filesystem, which may be incompatible with some older virtual drive and DVD burning applications. You’ll also need to play it on an actual Blu-ray player if you want to get the menus and such working correctly. If you’re looking to play it on a PC, a free trial of Arcsoft TMT is available here.

  What are you waiting for ? Grab a copy today !

  UPDATE : Here is an AVCHD-compliant version of the above, which should work better when burned on a DVD-5 instead of a BD-R. (mirror)
  

  What’s left before we have a fully free software Blu-ray creation toolkit ? Audio is already dealt with ; AC3 audio (aka Dolby Digital), the format used in DVD, is still supported by Blu-ray, and there are many free software AC3 encoders. The primary missing application is a free software Blu-ray authoring tool, to combine the video and audio streams to create a Blu-ray file structure with the menus, chapters, and so forth that we have all come to expect. But the hardest part is dealt with : we can now create compatible video and audio streams.

  In the meantime, x264 can be used to create streams to be authored using Blu-Print, Scenarist, Encore or other commercial authoring tools.

  More detailed documentation on the new Blu-ray support and how to use it can be found in the official commit message. Do keep in mind that you have to export to raw H.264 (not MKV or MP4) or else the buffering information will be slightly incorrect. Finally, also note that the encoding settings given as an example are not a good choice for general-purpose encoding : they are intentionally crippled by Blu-ray restrictions, which will significantly reduce compression for ordinary non-Blu-ray encoding.

  In addition to Blu-ray support, the aforementioned commit comes with a lot of fun extras :

  x264 now has native variable-framerate ratecontrol, which makes sure your encodes get a correct target bitrate and proper limiting of maximum bitrate even if the duration of every frame is different and the “framerate” is completely unknown. This helps a lot when encoding from variable-framerate container formats such as FLV and WMV, along with variable-framerate content such as anime.

  x264 now supports pulldown (telecine) in much the same fashion as it is handled in MPEG-2. The calling application can pass in flags representing how to display a frame, allowing easy transcoding from MPEG-2 sources with pulldown, such as broadcast television. The x264 commandline app contains some examples of these (such as the common 3:2 pulldown pattern).

  x264 now also exports HRD timing information, which is critical for compliant transport stream muxing. There is currently an active project to write a fully DVB-compatible free software TS muxer that will be able to interface with x264 for a seamless free software broadcast system. It will likely also be possible to repurpose this muxer as part of a free software Blu-ray authoring package.

  All of this is now available in the latest x264.

  http://mirror05.x264.nl/Dark/bluray%20fail.png