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• ffmpeg - how can I get a specific channel using channel masks (e.g. : get only surround left channel)

  26 novembre 2013, par awfulcode

  I'm trying to build a mixer that allows users to toggle specific channels on and off. I know that different codecs encode those channels in different orders (it's not as simple as getting channel #3 as the center channel every time), so the challenge is to properly identify the channel position in surround audio tracks.

  ffmpeg does list the in the beginning of libavutil/channel_layout.h :

  #define AV_CH_FRONT_LEFT             0x00000001
  
  #define AV_CH_FRONT_RIGHT            0x00000002
  
  #define AV_CH_FRONT_CENTER           0x00000004
  
  #define AV_CH_LOW_FREQUENCY          0x00000008
  
  #define AV_CH_BACK_LEFT              0x00000010
  
  #define AV_CH_BACK_RIGHT             0x00000020
  
  #define AV_CH_FRONT_LEFT_OF_CENTER   0x00000040
  
  #define AV_CH_FRONT_RIGHT_OF_CENTER  0x00000080
  
  #define AV_CH_BACK_CENTER            0x00000100
  
  #define AV_CH_SIDE_LEFT              0x00000200
  
  #define AV_CH_SIDE_RIGHT             0x00000400
  
  #define AV_CH_TOP_CENTER             0x00000800
  
  #define AV_CH_TOP_FRONT_LEFT         0x00001000
  
  #define AV_CH_TOP_FRONT_CENTER       0x00002000
  
  #define AV_CH_TOP_FRONT_RIGHT        0x00004000
  
  #define AV_CH_TOP_BACK_LEFT          0x00008000
  
  #define AV_CH_TOP_BACK_CENTER        0x00010000
  
  #define AV_CH_TOP_BACK_RIGHT         0x00020000
  
  #define AV_CH_STEREO_LEFT            0x20000000  ///< Stereo downmix.
  
  #define AV_CH_STEREO_RIGHT           0x40000000  ///< See AV_CH_STEREO_LEFT.
  
  #define AV_CH_WIDE_LEFT              0x0000000080000000ULL
  
  #define AV_CH_WIDE_RIGHT             0x0000000100000000ULL
  
  #define AV_CH_SURROUND_DIRECT_LEFT   0x0000000200000000ULL
  
  #define AV_CH_SURROUND_DIRECT_RIGHT  0x0000000400000000ULL
  
  #define AV_CH_LOW_FREQUENCY_2        0x0000000800000000ULL

  But looking over the header files and whatever little documentation about ffmpeg I couldn't find anything that tells me how to assign a specific channel position (or mask, as it's described in the header file) to a specific bus in a mixer audio unit.

  Do you know how to do that ? Please let me know if you want to look at the code I'm using right now.

  And as always, thank you so much.

• Connecting to RTSP stream via FFMpeg - 'could not find codec parameters for stream 0'

  14 novembre 2013, par user2992545

  I'm a beginner in the FFMpeg world, so please excuse me my overall level of knowledge and any mistakes.

  What I have here is a DVR, made by ITX Security. I have an SDK for it and currently I'm trying to connect to its RTSP using FFMPEG. I've been partially succesfull (i think), the best what I got was :

  `(...)bin>ffplay -user-agent "ITX Security" rtsp://ADMIN:1234@192.168.2.130:5554/live/
  
  
  
  [rtsp @ 02a242e0] UDP timeout, retrying with TCPB sq=0B f=0/0
  
  [rtsp @ 02a242e0] method PAUSE failed: 501 Not Implemented
  
  [rtsp @ 02a242e0] Could not find codec parameters for stream 0 (Video: h264):unspecified size Consider increasing the value for the 'analyzeduration' and 'probesize' options
  
  rtsp://ADMIN:1234@192.168.2.130:5554/live/: could not find codec parameters
  
  
  
  nan:  0.000 fd=0 aq=    0KB vq=    0KB sq=    0B f=0/0`

  Is it really indicating that it has trouble in playing the stream (because it lacks a proper codec ?) - or am I just not getting the point ?

  I've captured traffic between my computer and the DVR in question, and something is happening (at least that's what Wireshark says).

  https://www.dropbox.com/s/j65lige244kg8jt/rtsp_ffmpeg.pcap

  What am I doing wrong ?

  Regards.

• Decoding H.264 stream from dvr

  17 octobre 2013, par Andrew S

  I have a security DVR that uses h264 streams. I have been trying to get this to work with zoneminder. I have successfully logged into the dvr and recieved some form of data streams. The data stream is dumped to a fifo/pipe, and then zoneminder uses ffmpeg to read this in.

  Note : i know very very little about h.264 streams. just enough to be stupid.

  The video only updates about every 15 seconds in ZM. I can dump the stream to a file with ffmpeg or avconv (avconv -i /tmp/mypipe cam.mp4) but it is still not right. However, the file created by avconv is WAY WAY better than the one created by ffmpeg.

  I've included a link to the wireshark dump (I did change the PW and login info, etc...). From the data, It appears that the dvr is adding a header to the h264 data streams. I understand that the h264 stream starts with a (0x00 00 01 67) or (0x00 00 01 61). Here is an example of the header plus start of stream :

  0x33, 0x30, 0x64, 0x63, 0x48, 0x32, 0x36, 0x34, 
  
  0x3f, 0x55, 0x00, 0x00, 0x08, 0x00, 0x20, 0x00, 
  
  0xa2, 0x7a, 0xea, 0xdc, 0xcf, 0x08, 0x00, 0x00, 
  
  0x0d, 0x0a, 0x11, 0x07, 0x13, 0x20, 0x00, 0x00, 
  
  0x00, 0x00, 0x00, 0x01, 0x67, 0x42, 0xe0, 0x14, 
  
  0xdb, 0x05, 0x87, 0xc4, 0x00, 0x00, 0x00, 0x01, 
  
  0x68, 0xce, 0x30, 0xa4, 0x80, 0x00, 0x00, 0x00, 
  
  0x01, 0x06, 0xe5, 0x01, 0x51, 0x80, 0x00, 0x00, 
  
  0x00, 0x01, 0x65, 0xb8, 0x00, 0x01, 0xa8, 0xac,

  I can see that there are a few frame indicators in this message. The DVR's header appears to be 32 bytes long in this case, and in some other messages in the dump, it appears to be 24 bytes long. I am striping the header off before I dump the stream to the pipe. (I have verified the output doesn't include the dvr's headers in any way.

  What I would like help with is determining what I should be sending to the pipe. should I start with the first h.264 key ? Is there something out of order ? I'm very surprised that ffmpeg is only getting 15 second updates, but avconv is much better (lots of dropped frames, and playback is "sped up".

  using ffmpeg to read the pipe produces a file that shows it's codec as : H264 - MPEG-4 AVC (part 10) (avc1) with a Decoded format : Planar 4:2:0 YUV using vlc.

  Appreciate any help you can provide !

  Wireshark h264 dump

  edit : on Ubuntu 13.04
  ffmpeg version : 6:0.8.6-1ubuntu2
  avconv 0.8.6-6:0.8.6-1ubuntu2