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• MKV video playback shows a black picture and audio plays good

  24 mars 2023, par gbriones.gdl

  I have an MKV video file that has something wrong, every time I start my player, the video shows full black picture and the audio starts playing good, if I use the seek bar to position the playback anywhere in the time, then the video shows correct picture but audio stops playing, eventually (it takes several seconds) audio starts playing again in sync with video.

  


  The player I am using is the one in Kodi 20.1.0, I have tried enabling/disabling HW acceleration without success.

  


  I also tried VLC 3.0.16, which has a simmilar behavior with the exception that video starts showing from the very begining when opening the file, just when seeking the audio stops for several seconds.

  


  I also tried using ffmpeg to reencode the video with different codecs without success, I have tried multiple video and audio codec combinations, and also tried changing the pixel format.

  


  Then eventually I managed to fix the video by extracting streams into separate files, then merge them again, without reencoding, I thought that maybe something could be wrong with the metadata of the video, so I copied the same metadata and final output file still works fine. My question is how can I fix my video without having to split and merge streams ?

  


  Here is the info about my input file :

  


  $ ffmpeg -i S01E08.mkv 
ffmpeg version 4.4.2-0ubuntu0.22.04.1 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 11 (Ubuntu 11.2.0-19ubuntu1)
  configuration: --prefix=/usr --extra-version=0ubuntu0.22.04.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-pocketsphinx --enable-librsvg --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Input #0, matroska,webm, from 'S01E08.mkv':
  Metadata:
    ENCODER         : Lavf59.27.100
  Duration: 00:25:02.21, start: 0.000000, bitrate: 1382 kb/s
  Stream #0:0: Video: hevc (Main 10), yuv420p10le(tv, bt470bg/unknown/unknown, progressive), 1280x960, 59.94 fps, 59.94 tbr, 1k tbn, 59.94 tbc
    Metadata:
      ENCODER         : Lavc59.37.100 libx265
      DURATION        : 00:25:00.032000000
  Stream #0:1(spa): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp (default)
    Metadata:
      title           : Stereo
      DURATION        : 00:25:02.207000000
  Stream #0:2(jpn): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp
    Metadata:
      title           : Stereo
      DURATION        : 00:25:00.116000000
  Stream #0:3(spa): Subtitle: ass
    Metadata:
      ENCODER         : Lavc59.37.100 ssa
      DURATION        : 00:24:56.585000000
At least one output file must be specified


  


  Here are the steps I followed to fix the video, I had to use mkv format for the outputs because other formats were no good at writing metadata :

  


  ffmpeg -i S01E08.mkv -map 0:v:0 -c:v copy -map_metadata 0 video.mkv
ffmpeg -i S01E08.mkv -map 0:a:0 -c:a copy -map_metadata 0 audio1.mkv
ffmpeg -i S01E08.mkv -map 0:a:1 -c:a copy -map_metadata 0 audio2.mkv
ffmpeg -i S01E08.mkv -map 0:s -c:s copy -map_metadata 0 subs.mkv
ffmpeg -i video.mkv -i audio1.mkv -i audio2.mkv -i subs.mkv -map 0:v -map 1:a -map 2:a -map 3:s -c:v copy -c:a copy -c:s copy -map_metadata 0 -map_metadata 1 -map_metadata 2 -map_metadata 3 -disposition:s:0 0 -default_mode infer_no_subs video_audio.mkv


  


  I had to compare both input and output files :

  


  $ ffmpeg -i video_audio.mkv
ffmpeg version 4.4.2-0ubuntu0.22.04.1 Copyright (c) 2000-2021 the FFmpeg developers
  built with gcc 11 (Ubuntu 11.2.0-19ubuntu1)
  configuration: --prefix=/usr --extra-version=0ubuntu0.22.04.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libsrt --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-pocketsphinx --enable-librsvg --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 70.100 / 56. 70.100
  libavcodec     58.134.100 / 58.134.100
  libavformat    58. 76.100 / 58. 76.100
  libavdevice    58. 13.100 / 58. 13.100
  libavfilter     7.110.100 /  7.110.100
  libswscale      5.  9.100 /  5.  9.100
  libswresample   3.  9.100 /  3.  9.100
  libpostproc    55.  9.100 / 55.  9.100
Input #0, matroska,webm, from 'video_audio.mkv':
  Metadata:
    ENCODER         : Lavf58.76.100
  Duration: 00:25:02.21, start: 0.000000, bitrate: 1382 kb/s
  Stream #0:0: Video: hevc (Main 10), yuv420p10le(tv, bt470bg/unknown/unknown, progressive), 1280x960, 59.94 fps, 59.94 tbr, 1k tbn, 59.94 tbc (default)
    Metadata:
      ENCODER         : Lavc59.37.100 libx265
      DURATION        : 00:25:00.031000000
  Stream #0:1(spa): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp (default)
    Metadata:
      title           : Stereo
      DURATION        : 00:25:02.207000000
  Stream #0:2(jpn): Audio: aac (HE-AAC), 48000 Hz, stereo, fltp
    Metadata:
      title           : Stereo
      DURATION        : 00:25:00.116000000
  Stream #0:3(spa): Subtitle: ass
    Metadata:
      ENCODER         : Lavc59.37.100 ssa
      DURATION        : 00:24:56.585000000
At least one output file must be specified

$ ffprobe -show_streams S01E08.mkv > probe_bad.txt
$ ffprobe -show_streams video_audio.mkv > probe_good.txt
$ diff probe_bad.txt probe_good.txt 
32,33c32,33
< duration_ts=1502207
< duration=1502.207000
---
> duration_ts=N/A
> duration=N/A
40c40
< DISPOSITION:default=0
---
> DISPOSITION:default=1
53c53
< TAG:DURATION=00:25:00.032000000
---
> TAG:DURATION=00:25:00.031000000


  


  Then I thought that maybe the disposition flag in the video stream was causing the error, so I ran ffmpeg to copy all streams from my input video S01E08.mkv and added the disposition flag with the following command :

  


  ffmpeg -i S01E08.mkv -map 0:v -map 0:a:0 -map 0:a:1 -map 0:s -c:v copy -c:a copy -c:s copy -map_metadata 0 -disposition:v:0 default -disposition:s:0 0 -default_mode infer_no_subs test.mkv


  


  Still no luck, test.mkv shows no video when opening the file, I had to double check that disposition flag was changed :

  


  $ ffprobe -show_streams test.mkv > probe_bad2.txt
$ diff probe_bad.txt probe_bad2.txt 
40c40
< DISPOSITION:default=0
---
> DISPOSITION:default=1
53c53
< TAG:DURATION=00:25:00.032000000
---
> TAG:DURATION=00:25:00.031000000


  


  In other words I have to focibly split and merge to make the file work correctly. May be I need to set the duration and duration_ts of the video stream to N/A but I don't know how to do this.

  


• 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).

  


• Black overlay appears when merging a transparent video to another video

  13 juin 2012, par RakeshS

  This is what I have done so far :

  Command to create a transparent PNG image :

  convert -size 640x480 -background transparent -fill blue \
  
  -gravity South label:ROCK image1-0.png

  Command to create a transparent video :

  ffmpeg -loop 1 -f image2 -i image1-0.png -r 20 -vframes 100 \
  
  -vcodec png -pix_fmt bgra mov-1.mov

  (as per this post) - I expect this video to be a transparent video.

  Command to overlay a video with another :

  ffmpeg -i final-video.mov -sameq -ar 44100 \
  
  -vf "movie=mov-1.mov [logo];[in][logo] overlay=0:0 [out]" \
  
  -strict experimental final-video.mov

  Above commands works perfect and I have not faced any problem, but I don't get what I expect which is kinda watermarking effect, I want mov-1.mov to be transparent with final-video.mov.

  Questions :

  1. Is there any way to verify if the generated video is transparent ? other than merging ?
  2. Not sure why the above mov-1.mov is not transparent when it is merged with final-video.mov, any info to solve this problem would be great.

  Please help.