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• How to use ffmpeg on android with JNI folder

  25 août 2016, par soheila

  I have a question.
  I want to use ffpmeg library on android (convert pictures to video, convert videos to gif files and etc...)
  Do I have to know C programming or not ?

• how can I assign unique AVFoundation camera device names ?

  28 avril 2023, par mcgregor94086

  Short summary :
I have a USB multi-camera array device. According to system_profiler, each of these webcams share the same name : "USB Camera". I have no unique name I can use with FFMPEG AVFoundation and get images from that specific camera. How can I tell FFMPEG the specific camera that I want (each has a unique USB path that I normally use to identify a specific camera.

  


  I can solve this problem on Linux, but I can't figure out how to do it on macOS.

  


  How I might do this on Linux
I know the unique USB Path to each camera, and I would like to use this to assign a unique Name that I can address using FFMPEG when taking images. On Linux I can use the udev system to make those assignments,

  


  In Linux, I can reassign a new unique camera name using /etc/udev/rules.d/60-v4l.rules. with something like this :

  


  SUBSYSTEMS=="usb", ENVID_VENDOR_ID=="0bda", ENVID_MODEL_ID=="5829", ENVID_PATH_TAG==platform-fd500000_pcie-0000_01_00_0-usb_1_4_5_1_3_1_1, ENVID_V4L_PRODUCT="Cam_00"
SUBSYSTEMS=="usb", ENVID_VENDOR_ID=="0bda", ENVID_MODEL_ID=="5829", ENVID_PATH_TAG==platform-fd500000_pcie-0000_01_00_0-usb_1_4_5_1_3_1_3, ENVID_V4L_PRODUCT="Cam_01"
...

  


  More details :
Of course macOS doesn't work this way, as it uses AVFoundation to address video devices.

  


  When I attach the device I see that 16 new cameras now appear when I type query system_profiler SPCameraDataType, it prints the output shown further below

  


  You may notice that there are 16 cameras all named "USB Camera :" but system_profiler is reporting that each has a "Unique ID :" that is different for each camera. This Unique ID is composed of a unique USB Path (e.g. '0x1441311') concatenated with the "Vendor ID" ('00bda') and product ID ('5829') all expressed in hexadecimal.

  


  Unfortunately, this means every camera has the same generic name in iPhoto, and when specifying the input camera in FFMPEG with AVFoundation syntax, I can't seem to indicate which specific camera I want.

  


  I want to take 1 photo from each camera in a specific order. I have a table that maps each camera's USB Path to a desired name that would make it easy for me to trigger the camera captures in the sequence I desire.

  


  In Linux, I can reassign a new unique camera name using /etc/udev/rules.d/60-v4l.rules.

  


  SUBSYSTEMS=="usb", ENVID_VENDOR_ID=="0bda", ENVID_MODEL_ID=="5829", ENVID_PATH_TAG==platform-fd500000_pcie-0000_01_00_0-usb_1_4_5_1_3_1_1, ENVID_V4L_PRODUCT="Cam_00"
SUBSYSTEMS=="usb", ENVID_VENDOR_ID=="0bda", ENVID_MODEL_ID=="5829", ENVID_PATH_TAG==platform-fd500000_pcie-0000_01_00_0-usb_1_4_5_1_3_1_3, ENVID_V4L_PRODUCT="Cam_01"
...

  


  % system_profiler SPCameraDataType

  


  Camera :

  


  USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144131100bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144200000bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144141400bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144131300bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144141300bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144121200bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144121400bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144133000bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144131200bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144141100bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144143000bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144121300bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144110000bda5829

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144141200bda5829

FaceTime HD Camera (Built-in):

  Model ID: UVC Camera VendorID_1452 ProductID_34068
  Unique ID: 0x8020000005ac8514

USB Camera:

  Model ID: UVC Camera VendorID_3034 ProductID_22569
  Unique ID: 0x144300000bda5829


  


  MacBook Pro, OS X 10.11
Posted on Apr 27, 2023 10:49 PM
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• avcodec/rv34 : Don't needlessly copy VLC length and symbol arrays

  22 octobre 2020, par Andreas Rheinhardt

  avcodec/rv34 : Don't needlessly copy VLC length and symbol arrays
  Most of the VLCs used by RealVideo 3 and 4 obey three simple rules :
  
  Shorter codes are on the left of the tree, for each length, the symbols
  
  are ascending from left to right and the symbols either form a
  
  permutation of 1..size or 0..(size - 1). For the latter case, one just
  
  needs to store the length of each symbol and create the codes according
  
  to the other rules ; no explicit code or symbol array must be stored.
  
  The former case is also treated in much the same way by artificially
  
  assigning a length of zero to the symbol 0 ; when a length of zero was
  
  encountered, the element was ignored except that the symbol counter was
  
  still incremented. If the length was nonzero, the symbol would be
  
  assigned via the symbol counter and the length copied over into a new
  
  array.
  Yet this is unnecessary, as ff_init_vlc_sparse() follows exactly the
  
  same pattern : If a length of zero is encountered, the element is ignored
  
  and only the symbol counter incremented. So one can directly forward the
  
  length array and also need not create a symbol table oneself, because
  
  ff_init_vlc_sparse() will infer the same symbol table in this case.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/rv34.c