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• Need help on handling MPEG4V1 data

  14 septembre 2011, par Gediminas

  I'm in situation where I need to get a chunk of MPEG4V1 (Microsoft MPEG-4 VKI
  Codec V1) data located in the beginning of a packet (that was sent by some DVR unit).

  Packet structure looks something like this :

  • Compressed MPEG4 data.
  • Long integer - Number of events and tripwires.
  • Long integer - Number of events.
  • Event - Event's sequence.
  • Long integer - Number of tripwires.
  • Tripwire - Tripwires sequence.
  • Long integer - Cyclical redundant code (CRC).

  So there is no indication of how to know where does the MPEG4 data ends (Or is there ?),
  and from where should I start reading this additional data like "Number of events and tripwires" and etc...

  I uploaded two packet's so you could see how the actual data looks like :
  recvData1.txt,
  recvData2.txt.

  I've tried to decode those packets using FFmpeg library with avcodec_decode_video function and by removing byte by byte from the end of my recvData buffer in a hope for any results,
  but FFmpeg just allways returned with an error messages like this :

  "[msmpeg4v1 @ 038865a0] invalid startcode",
  "[msmpeg4v1 @ 038865a0] header damaged".

  I'm not that good specialist on knowing of how does the MPEG4 works from the inside,
  but judging by the error messages it's clearly seen that I'm missing some data for decoding at the start of the buffer.

  So I'm not sure of what part / kind of MPEG data I'm getting here..
  Maybe it's some kind of MPEG's "frame" data with it's "end" indication or something ?

  I've even compared the start of my recvData buffer to some of MPEG4V1 encoded video files I found on the net "http://www.trekmania.net/clips/video_clips4.htm" to check if the start of my buffer really contains the MPEG data ..and not some kind of DVR vendor specific stuff..

  And I noticed that there are about 20bytes of data
  (at the start of my packet data, and in .avi files right after about 180bytes..)
  that looks like some kind of header or something..

  Please check this image : "http://ggodis.gamedev.lt/stackOverflow/recvData.jpg"

  Maybe someone knows what this part of MPEG4V1 data represents ?

  P.S. ..I've checked the CRC values for my received packets and they were correct..

• FFMPEG with hardware codec support

  28 janvier 2012, par mctma

  I have built a simple media player using ffmpeg on Android 2.2. Hardware is an arm cortex-a8 based 1GHz processor, 512 MB RAM. I am getting low performance, around 15 FPS for 800x600 mp4 video. I have a couple of questions on how I can improve the performance

  • How can I use the hardware codecs available on my target device. How can I configure ffmpeg to use the available hardware decoders ? Does the GPU or graphics driver have to expose some standard API like OpenMax IL in order to this ?

  • What are the options that should be enabled when building ffmpeg so that it can be optimized for my target hardware ? Something like :
    --cpu=cortex=a8 --extra-cflags="-mfpu=neon" ...

  I have already looked around the net but I couldn't find the answers that I am looking for. I hope someone can advice me on this.

  Thanks in advance !

• Dreamcast Development Desktop

  28 mars 2011, par Multimedia Mike — Sega Dreamcast

  Some people are curious about what kind of equipment is required to program a Sega Dreamcast. This is my setup :

  
  
  

  It’s a bit overcomplicated. The only piece in that picture which doesn’t play a role in the Dreamcast development process is the scanner. The Eee PC does the heavy lifting of development (i.e., text editing and cross compilation) and uploads to the Dreamcast via a special serial cable. Those are the most essential parts and are really the only pieces necessary for a lot of algorithmic stuff (things that can be validated via a serial console). But then I have to go up a level where I output video. That’s where things get messy.

  
  
  

  The Mac Mini and giant monitor really just act as a glorified TV in this case. Ideally, it will be more than that. The DC outputs audio and video via composite cables to a Canopus DV capture bridge. That’s connected via FireWire to the external hard drive underneath the Mac Mini, which is connected to the Mac. Adobe Premiere Pro handles the DV capture / display.

  One day I hope to have something worthwhile to capture.