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• v4l2 learning resources step by step [closed]

  5 août 2023, par Mark Watts

  I intend to learn how v4l2 works and how is a hw codec integrated to do decoding
What resources do i need and where to start ? i'm new to kernel space too

  


  

  1. Hardware board ? ( Raspberry pi or similar ?)

  


  2. Environment ( VMware ?)

  


  3. Example code with userspace Multimedia framework using v4l2 driver ( where can i see examples of this stuff that is already done ?)

  


  4. Documentation / turorials / videos

  


  


  Ive come across some videos from bootlin and the kernel documentation . I want to know how to approach it methodically.

  


• FFmpeg for Android platform

  30 avril 2014, par Neeraj

  I am trying to create an android application that uses FFMpeg. For that, I downloaded the FFmpeg code(v 0.8.15) from http://www.ffmpeg.org/olddownload.html. And compiled the code as per instructions given at http://www.roman10.net/how-to-build-ffmpeg-for-android/

  As a result, .a files have been generated in Android/lib folder & .h files in android/include folder.

  But, when I try to create .so file of my Native code what uses this prebuilt FFmpeg library (.a files), it gives undefined reference errors.

  Please find my project’s code structure is given below.

  project path is /home/guest/Neeraj_temp/FFMpeg-Example

  At this path, I created two folders jni & prebuilt
  In prebuilt folder, I kept libavfilter.a, libavcodec.a, libavformat.a, libavutil.a, libswscale.a
  In jni folder, I kept one include folder that contains all .h folders (libavcodec, libavfilter, libavformat, libavutil, libswscale).

  api-example.c file is also kept in jni folder that uses FFmpeg’s APIs.
  & one Android.mk file in jni folder.

  Android.mk :-

  LOCAL_PATH:= $(call my-dir)
  
  include $(CLEAR_VARS)
  
  LOCAL_MODULE    := libFFmpeg
  
  LOCAL_C_INCLUDES := $(LOCAL_PATH)/FFMpeg/include
  
  LOCAL_SRC_FILES := api-example.c
  
  LOCAL_LDLIBS += -L$(LOCAL_PATH)/../prebuilt -lavfilter -lavutil -lavformat -lavcodec -lswscale
  
  include $(BUILD_SHARED_LIBRARY) 

  Error :

  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wavpack.c:689: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(wavpack.o): In function `wv_unpack_stereo':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wavpack.c:604: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wavpack.c:608: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(wavpack.o):/home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wavpack.c:1215: more undefined references to `av_log' follow
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(wmavoice.o): In function `synth_block_fcb_acb':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wmavoice.c:1359: undefined reference to `av_memcpy_backptr'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(wmavoice.o): In function `synth_frame':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wmavoice.c:1441: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(wmavoice.o): In function `synth_superframe':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wmavoice.c:1765: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(wmavoice.o): In function `wmavoice_decode_packet':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wmavoice.c:1919: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(wmavoice.o): In function `wmavoice_decode_init':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wmavoice.c:350: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wmavoice.c:373: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(wmavoice.o):/home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wmavoice.c:397: more undefined references to `av_log' follow
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(wnv1.o): In function `decode_frame':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/wnv1.c:81: undefined reference to `av_reverse'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(ws-snd1.o): In function `ws_snd_decode_frame':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/ws-snd1.c:70: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/ws-snd1.c:83: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/ws-snd1.c:79: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(xan.o): In function `xan_decode_frame':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/xan.c:568: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/xan.c:551: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(xan.o):/home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/xan.c:515: more undefined references to `av_log' follow
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(xan.o): In function `xan_unpack':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/xan.c:178: undefined reference to `av_memcpy_backptr'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(xl.o): In function `decode_frame':
  
  /home/guest/Neeraj_temp/ffmpeg-0.8.15/libavcodec/xl.c:60: undefined reference to `av_log'
  
  /home/guest/Neeraj_temp/FFMpeg-Example/jni/../prebuilt/libavcodec.a(xsubdec.o): In function `decode_frame'

  I have read a lot of blogs but still not able to get the solution. Kindly provide me the solution. How do I need to structure the code that I should not get these errors & get the code compiled.

  Thanks.

• Can't access Google Cloud Platform hosted rtsp stream externally

  1er novembre 2023, par Nikos Daskalas

  I have been trying to host a video to rtsp stream on a gcp vm instance.

  


  My steps were :

  


  a) Set up an external ip to my vm, and setup firewall rules to allow traffick.

  


  b)Install mediamtx to my vm and start a server with ./mediamtx

  


  c)install ffmpeg and stream my video with : ffmpeg -i video.mp4 -rtsp_transport tcp -f rtsp rtsp ://externalip:8554/live.stream

  


  The stream runs locally, but when I try to access in with vlc or ffplay rtsp ://externalip:8554/live.stream, I cannot connect. I tried to ping the server from the client side, and it works ok.

  


  What am I missing ? Are there any more configurations I need to do to my project ?