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• What is ffmpeg, avcodec, x264 ? [closed]

  26 février 2016, par onmyway133

  From wiki, I read that

  FFmpeg is a free software project that produces libraries and programs
  for handling multimedia data. The most notable parts of FFmpeg are
  libavcodec, an audio/video codec library used by several other
  projects, libavformat, an audio/video container mux and demux library,
  and the ffmpeg command line program for transcoding multimedia files.

  So ffmpeg is a wrapper of avcodec ? And I often hear that people encode video with x264 using ffmpeg. So ffmpeg is also a wrapper of x264 ?

  How are they related ?

• Who Invented FLIC ?

  26 mai 2011, par Multimedia Mike — Multimedia History

  I have been reading through “All Your Base Are Belong To Us : How 50 Years of Video Games Conquered Pop Culture” by Harold Goldberg. Despite the title, Zero Wing has yet to be mentioned (I’m about halfway done).

  
  
  

  I just made it through the chapter describing early breakthrough CD-ROM games, including Myst, The 7th Guest, and The 11th Hour. Some interesting tidbits :

  The 7th Guest
  Of course, Graeme Devine created a new FMV format (called VDX, documented here) for The 7th Guest. The player was apparently called PLAY and the book claims that Autodesk was so impressed by the technology that it licensed the player for use in its own products. When I think of an Autodesk multimedia format, I think of FLIC. The VDX coding format doesn’t look too much like FLIC, per my reading.

  Here’s the relevant passage (pp 118-119) :

  Devine began working on creating software within the CD-ROM disk that would play full-motion video. Within days he had a robust but small ninety-kilobyte player called PLAY that was so good, it was licensed by Autodesk, the makers of the best 3-D animation program at the time. Then Devine figured out a way to compress the huge video files so that they would easily fit on two CD-ROMs.

  Googling for “autodesk trilobyte play program” (Trilobyte was the company behind 7th Guest) led me to this readme file for a program called PLAY73 (hosted at Jason Scott’s massive CD-ROM archive, and it’s on a disc that, incidentally, I donated to the archive ; so, let’s here it for Jason’s tireless archival efforts ! And for Google’s remarkable indexing prowess). The file — dated September 10, 1991 — mentions that it’s a FLICK player, copyright Trilobyte software.

  
  
  

  However, it also mentions being a Groovie Player. Based on ScummVM’s reimplementation of the VDX format, Groovie might refer to the engine behind The 7th Guest.

  So now I’m really interested : Did Graeme Devine create the FLIC file format ? Multimedia nerds want to know !

  I guess not. Thanks to Jim Leonard for digging up this item : “I developed the flic file format for the Autodesk Animator.” Jim Kent, Dr. Dobbs Magazine, March 1993.

  The PLAY73 changelog reveals something from the bad old days of DOS/PC programming : The necessity of writing graphics drivers for 1/2 dozen different video adapters. The PLAY73 readme file also has some vintage contact address for Graeme Devine ; remember when addresses looked like these ?

  If you have any comments, please send them to :
  	Compuserve : 72330,3276
  	Genie : G.DEVINE
  	Internet : 72330,3276@compuserve.com
  

  The 11th Hour
  The book didn’t really add anything I didn’t already know regarding the compression format (RoQ) used in 11th Hour. I already knew how hard Devine worked at it. This book took pains to emphasize the emotional toll taken on the format’s creator.

  I wonder if he would be comforted to know that, more than 15 years later, people are still finding ways to use the format.

• Further SMC Encoding Work

  25 août 2011, par Multimedia Mike — General

  Sometimes, when I don’t feel like doing anything else, I look at that Apple SMC video encoder again.

  8-bit Encoding
  When I last worked on the encoder, I couldn’t get the 8-color mode working correctly, even though the similar 2- and 4-color modes were working fine. I chalked the problem up to the extreme weirdness in the packing method unique to the 8-color mode. Remarkably, I had that logic correct the first time around. The real problem turned out to be with the 8-color cache and it was due to the vagaries of 64-bit math in C. Bit shifting an unsigned 8-bit quantity implicitly results in a signed 32-bit quantity, or so I discovered.

  Anyway, the 8-color encoding works correctly, thus shaving a few more bytes off the encoding size.

  Encoding Scheme Oddities
  The next step is to encode runs of data. This is where I noticed some algorithmic oddities in the scheme that I never really noticed before. There are 1-, 2-, 4-, 8-, and 16-color modes. Each mode allows encoding from 1-256 blocks of that same encoding. For example, the byte sequence :

    0x62 0x45
  

  Specifies that the next 3 4×4 blocks are encoded with single-color mode (of byte 0×62, high nibble is encoding mode and low nibble is count-1 blocks) and the palette color to be used is 0×45. Further, opcode 0×70 is the same except the following byte allows for specifying more than 16 (i.e., up to 256) blocks shall be encoded in the same matter. In light of this repeat functionality being built into the rendering opcodes, I’m puzzled by the existence of the repeat block opcodes. There are opcodes to repeat the prior block up to 256 times, and there are opcodes to repeat the prior pair of blocks up to 256 times.

  So my quandary is : What would the repeat opcodes be used for ? I hacked the FFmpeg / Libav SMC decoder to output a histogram of which opcodes are used. The repeat pair opcodes are never seen. However, the single-repeat opcodes are used a few times.

  Puzzle Solved ?
  I’m glad I wrote this post. Just as I was about to hit “Publish”, I think I figured it out. I haven’t mentioned the skip opcodes yet– there are opcodes that specify that 1-256 4×4 blocks are unchanged from the previous frame. Conceivably, a block could be unchanged from the previous frame and then repeated 1-256 times from there.

  That’s something I hadn’t thought of up to this point for my proposed algorithm and will require a little more work.

  Further reading

  • My first entry regarding my toy SMC encoder