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• Using OpenCV 2.4.4 with FFmpeg in Windows

  22 décembre 2015, par aardvarkk

  I know there are other questions dealing with FFmpeg usage in OpenCV, but most of them appear to be outdated.

  By opening up the makefiles in CMake, I can verify that I’ve got the WITH_FFMPEG flag on. My output folder for the OpenCV build contains a bin folder, within which are Debug and Release folders, each containing a copy of a .dll file entitled opencv_ffmpeg244.dll. I can step into the source code of OpenCV when I create a VideoWriter and verify that the function pointers to the .dll get filled correctly. That much appears to be working.

  If I use the FOURCC code of CV_FOURCC_PROMPT, the following codecs work properly :

  • Microsoft Video 1
  • Intel IYUV codec
  • Logitech Video (I420)
  • Cinepak Codec by Radius
  • Full Frames (Uncompressed)

  The following codecs do not work properly (ie. produce a 0kb video file) :

  • Microsoft RLE

  If my understanding is correct, using FFMPEG should allow for encoding video using a whole bunch of new codecs (x264, DIVX, XVID, and so on). However, none of these appear in the prompt. Manually setting them by their FOURCC codes using the macro CV_FOURCC(...) also doesn’t work. For instance, using this : CV_FOURCC('X','2','6','4') produces the message :

  Could not find encoder for codec id 28: Encoder not found

  and makes a video file of size 0kb.

  Using this : CV_FOURCC('X','V','I','D') produces no error message, and makes a video file of 6kb that will not play in Windows Media Player or VLC.

  I tried manually downloaded the Xvid codec from Xvid.org. Once that was installed, it appeared under the VFW selection in the prompt, and the encoding worked properly. So it’s close to a solution, but if I try to set the FOURCC code directly, it still fails as above ! I have to pick it from the prompt every time. Isn’t FFmpeg supposed to include a whole bunch of codecs ? If so, why am I manually downloading the codec instead of using the one built into FFmpeg ?

  What am I missing here ? Is there a way to check that FFMPEG is "enabled" ? It seems like the only codecs available in the prompt are VFW codecs, not the FFMPEG ones. The .dll has been built and is sitting in the same folder as the executable, but it appears it’s not being used in any way.

  Lots of related questions here. Hoping to find somebody knowledgeable about the FFmpeg implementation in OpenCV and with some knowledge of how all of these pieces fit together.

• lavfi/sidedata : add filter for manipulating frame side data

  5 octobre 2016, par Marton Balint

  lavfi/sidedata : add filter for manipulating frame side data
  This is a similar filter to f_metadata, only it works on side data. Since
  
  adding side data from a user provided arbitrary binary string is unsafe,
  
  because current code assumes that a side data of a certain kind has the proper
  
  size, this filter only implements selection and deletion. Also, no value
  
  matching support is implemented yet, because there is no uniform way to specify
  
  a side data textually.
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] Changelog
  • [DH] doc/filters.texi
  • [DH] libavfilter/Makefile
  • [DH] libavfilter/allfilters.c
  • [DH] libavfilter/f_sidedata.c
  • [DH] libavfilter/version.h

• Rails 5 - Video streaming using Carrierwave uploaded video size constraint on the server

  21 mars 2020, par Milind

  I have a working Rails 5 apps using Reactjs for frontend and React dropzone uploader to upload video files using carrierwave.

  So far, what is working great is listed below -

  1. User can upload videos and videos are encoded based on the selection made by user - HLS or MPEG-DASH for online streaming.
  2. Once the video is uploaded on the server, it starts streaming it by :-
     • FIRST,copying video on /tmp folder.
     • Running a bash script that uses ffmpeg to transcode uploaded video using predefined commands to produce new fragments of videos inside /tmp folder.
     • Once the background job is done, all the videos are uploaded on AWS S3, which is how the default carrierwave works
  3. So, when multiple videos are uploaded, they are all copied in /tmp folder and then transcoded and eventually uploaded to S3.

  My questions, where i am looking some help are listed below -

  1- The above process is good for small videos, BUT what if there are many concurrent users uploading 2GB of videos ? I know this will kill my server as my /tmp folder will keep on increasing and consume all the memory, making it to die hard.How can I allow concurrent videos to upload videos without effecting my server’s memory consumption ?

  2- Is there a way where I can directly upload the videos on AWS-S3 first, and then use one more proxy server/child application to encode videos from S3, download it to the child server, convert it and again upload it to the destination ? but this is almost the same but doing it on cloud, where memory consumption can be on-demand but will be not cost-effective.

  3- Is there some easy and cost-effective way by which I can upload large videos, transcode them and upload it to AWS S3, without effecting my server memory. Am i missing some technical architecture here.

  4- How Youtube/Netflix works, I know they do the same thing in a smart way but can someone help me to improve this ?

  Thanks in advance.