Recherche avancée

Sur d’autres sites (4827)

• lavf/matroskadec : Normalize noncompliant A_QUICKTIME/V_QUICKTIME private data

  10 janvier 2016, par Mats Peterson

  lavf/matroskadec : Normalize noncompliant A_QUICKTIME/V_QUICKTIME private data
  This patch adds a new static function get_qt_codec() that takes care of
  
  the initial retrieval of the fourcc and codec ID for A_QUICKTIME and
  
  V_QUICKTIME. It also normalizes noncompliant private data found in some
  
  older files that incorrectly starts with the fourcc by expanding/shifting
  
  the data by 4 bytes, and storing the data size at the start. This is
  
  necessary in order for the rest of the code in the A_QUICKTIME and
  
  V_QUICKTIME blocks (and most likely other code as well) to correctly
  
  parse the private data.
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/matroskadec.c

• ffmpegthumbnailer issue : dyld : Library not loaded : /usr/local/lib/libavutil.52.18.100.dylib

  18 octobre 2013, par scientiffic

  When I try to run ffmpegthumbnailer, I get the following error :

  dyld: Library not loaded: /usr/local/lib/libavutil.52.18.100.dylib
  
    Referenced from: /usr/local/bin/ffmpegthumbnailer
  
    Reason: image not found
  
    Trace/BPT trap: 5

  I installed ffmpeg using the directions here :

  http://ffmpeg.org/trac/ffmpeg/wiki/MacOSXCompilationGuide

  In my /usr/local/lib folder, I have the file "libavutil.a", but not the one specified in the error mesage.

  How can I solve this error ?

  This is what I was using to try to generate a thumbnail :

  ffmpegthumbnailer -i /public/uploads/tmp/1382121359-37490-7826/thumb_Untitled.mov -o /public/uploads/tmp/1382121359-37490-7826/tmpfile.png -c png -q 10 -s 158

• Making Sure The PNG Gets There

  14 juin 2013, par Multimedia Mike — General

  Rewind to 1999. I was developing an HTTP-based remote management interface for an embedded device. The device sat on an ethernet LAN and you could point a web browser at it. The pitch was to transmit an image of the device’s touch screen and the user could click on the picture to interact with the device. So we needed an image format. If you were computing at the time, you know that the web was insufferably limited back then. Our choice basically came down to GIF and JPEG. Being the office’s annoying free software zealot, I was championing a little known up and coming format named PNG.

  So the challenge was to create our own PNG encoder (incorporating a library like libpng wasn’t an option for this platform). I seem to remember being annoyed at having to implement an integrity check (CRC) for the PNG encoder. It’s part of the PNG spec, after all. It just seemed so redundant. At the time, I reasoned that there were 5 layers of integrity validation in play.

  I don’t know why, but I was reflecting on this episode recently and decided to revisit it. Here are all the encapsulation layers of a PNG file when flung over an ethernet network :

  
  
  

  So there are up to 5 encapsulations for the data in this situation. At the innermost level is the image data which is compressed with the zlib DEFLATE method. At first, I thought that this also had a CRC or checksum. However, in researching this post, I couldn’t find any evidence of such an integrity check. Further, I don’t think we bothered to compress the PNG data in this project long ago. It was a small image, monochrome, and transferring via LAN, so the encoder could get away with signaling uncompressed data.

  The graphical data gets wrapped up in a PNG chunk and all PNG chunks have a CRC. To transmit via the network, it goes into a TCP frame, which also has a checksum. That goes into an IP packet. I previously believed that this represented another integrity check. While an IP frame does have a checksum, the checksum only covers the IP header and not the payload. So that doesn’t really count towards this goal.

  Finally, the data gets encapsulated into an ethernet frame which has — you guessed it — a CRC.

  I see that other link layer protocols like PPP and wireless ethernet (802.11) also feature frame CRCs. So I guess what I’m saying is that, if you transfer a PNG file over the network, you can be confident that the data will be free of any errors.