Recherche avancée

Sur d’autres sites (14083)

• Linux : Create a file for writing with controlled flushing to disk in large chunks [closed]

  12 août 2023, par Pete

  On Linux I have a process (ffmpeg) that writes very slowly (even slower than 1kb / s sometimes) to disk. Ffmpeg can buffer this to 256kb chunks that get written infrequently but ffmpeg hangs occasionally and if I try to detect these hangs by checking that the file is being updated I need to wait a long time between updates, up to 10 or 15 mins, otherwise I can sometimes mistakenly kill the ffmpeg process when it appears to have stopped writing when it fact its still filling its internal buffer.

  


  Theres no way to detect this it seems unless I use strace (that I can find anyway). So I am wondering about turning off buffering in ffmpeg and writing unbuffered to disk from ffmpeg.

  


  This will result in the disk constantly making tiny writes and wasting power (and probably, if I use a SSD, mess with wear levelling too).

  


  So I would like to make ffmpeg write to a 'virtual file' (in memory - either kernel memory or a process) which I can specify the flushing characteristics of. The idea being to perhaps specify flush every 2 minutes, then I can keep an eye on the file size and make sure its still being written.

  


  I don't think I've missed any other ways to do this job - even if I could watch the socket stream incoming to ffpmeg the process itself could still stop writing and lose data. Doing the buffering outside of ffmpeg seems like the best way.

  


  Is there a built in way to do this in Linux or does it mean a custom process ? I guess I know how to do this with a small C program and pipe the data in but I wonder if theres a neater way.

  


• Opencv VideoCapture not streaming RTSP link and returns "no frame !"

  6 septembre 2023, par Asadullah Naeem

  I am trying to stream my HikVision IP camera throough python. I am using cv2.VideoCapture("rtsp_link") which works fine on my Laptop but when I try to run the same python script with same Opencv and FFmpeg version it gives me following error :

  


  Error :

  


  [h264 @ 000002124c7f9a40] missing picture in access unit with size 47
[h264 @ 000002124c7f9a40] no frame!


  


  I have so far tried to run this script on 5 computer devices but it gives the same error. I am using the following python script and my Opencv version is 4.6.0.66 and ffmpeg version 2022-06-20-git-56419428a8-essentials_build-www.gyan.dev :

  


  Python Script :

  


  import cv2

# RTSP stream URL
rtsp_url = "rtsp://username:password@ip_address:port/Streaming/Channels/501"

# Open the RTSP stream
cap = cv2.VideoCapture(rtsp_url)

# Check if the stream was successfully opened
if not cap.isOpened():
    print("Failed to open RTSP stream.")
    exit()

# Read and display frames from the stream
while True:
    # Read a frame from the stream
    ret, frame = cap.read()

    # Check if the frame was successfully read
    if not ret:
        print("Failed to read frame from RTSP stream.")
        break

    # Display the frame
    cv2.imshow("RTSP Stream", frame)

    # Exit if 'q' is pressed
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

# Release the resources
cap.release()
cv2.destroyAllWindows()



  


  Update :

  


  Code runs on a laptop on both wifi and mobile internet (4G) but on other devices rtsp link is accessible only with mobile internet (4G).

  


• "Relocation cannot be used against local symbol" only for one platform (x86)

  10 janvier 2023, par JonasVautherin

  Problem

  


  I am cross-compiling gstreamer using Meson, and it works for 3 different platforms (android-arm, android-arm64, android-x86_64) but fails for android-x86 with errors like :

  


  ld: error: relocation R_386_32 cannot be used against local symbol; recompile with -fPIC


  


  I can't seem to understand which component was not built with -fPIC, and I don't understand why this would differ between the 4 platforms. If 3 are built with -fPIC, why would the fourth be different ?

  


  Details

  


  More specifically, it fails with a bunch of the following errors :

  


  FAILED: subprojects/FFmpeg/test_avcodec_utils
/usr/i686-linux-android/bin/clang  -o subprojects/FFmpeg/test_avcodec_utils subprojects/FFmpeg/test_avcodec_utils.p/libavcodec_tests_utils.c.o -Wl,--as-needed -Wl,--no-undefined -Wl,-O1 -pie -Wl,-Bsymbolic -fPIC -Wl,--start-group subprojects/FFmpeg/libavcodec-static.a subprojects/FFmpeg/libavutil.a subprojects/FFmpeg/libavutil-static.a subprojects/FFmpeg/libswresample.a subprojects/FFmpeg/libswresample-static.a -pthread -lm -lz -lz -Wl,--end-group
ld: error: relocation R_386_32 cannot be used against local symbol; recompile with -fPIC
>>> defined in subprojects/FFmpeg/libavcodec-static.a(libavcodec-static.a.p/dirac_dwt.o)
>>> referenced by x86util.asm:1315 (/work/build/android-x86/dependencies/gstreamer/gstreamer/src/gstreamer/subprojects/FFmpeg/libavutil/x86/x86util.asm:1315)
>>>               libavcodec-static.a.p/dirac_dwt.o:(.text+0x9F) in archive subprojects/FFmpeg/libavcodec-static.a


  


  I essentially run $ meson setup --cross-file my-crossfile build . in a Dockcross container, with some options, so nothing special there as far as I can tell.

  


  My cross-file looks like this (similar to the other 3 that work, except for cpu and cpu_family that differ) :

  


  [constants]
cross_triple = 'i686-linux-android'
cross_root = '/usr/' + cross_triple

[properties]
pkg_config_libdir = ''

[binaries]
c = cross_root + '/bin/clang'
cpp = cross_root + '/bin/clang++'
ar = cross_root + '/bin/llvm-ar'
as = cross_root + '/bin/llvm-as'
ranlib = cross_root + '/bin/llvm-ranlib'
ld = cross_root + '/bin/ld'
strip = cross_root + '/bin/llvm-strip'
pkgconfig = 'pkg-config'

[host_machine]
system = 'android'
cpu_family = 'x86'
cpu = 'i686'
endian = 'little'