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• creation of video file with alpha channel/transparency

  3 décembre 2015, par boerfi

  I’m experimenting with a video file with alpha channel.
  Later on the file should be an overlay for another video. It will be merged with another file in real time and saved to another file. But that is not the important point. The problem starts earlier because I can’t even play it.

  The video is a png-encoded Quicktime-file which I cannot play with any video player. WMP, VLC, MPC and ffplay all show various problems which all lead to the problem that the images seem to get decoded too slowly.
  The strange thing is that neither cpu (i7) nor my ssd are on limit but the file isn’t played correctly.

  Since the problem appears with all players I think it’s based on using png in video. I googled but didn’t find a proper way to create a partly transparent video file.
  I tried various methods of exporting (with adobe media encoder) with no result : the file lost its transparency or is running too slow.

  The resulting file which I create with my SDK is correct (video and audio are synchronous and fluid) but it takes 1 minute to render a video of 40 seconds although it works in real time with files without transparency.

  Does anyone know what kind of file I should export that has a minimum resolution of 720p, that is partly transparent and that can be played with ffplay in real time ?
  I would also appreciate any experiences with partly transparent videos which could help me because I couldn’t find any helpful links ?

  Thanks,
  Marius

• Synchronize raspicam video and arecord for ffmpeg rtmp streaming

  6 mars 2017, par Роман Мальцев

  I’m trying to synchronize video and audio from my raspicam and arecord and make rtmp stream with ffmpeg and 3g modem, but don’t know how to do that. I have tried with this code :

  raspivid -t 0 -w 1024 -h 768 -fps 25 -vf -hf -b 1000000 -v -o temp.v & arecord -f cd -D plughw:0 | ffmpeg -i temp.v -itsoffset 13.5 -i - -c:v copy -c:a libmp3lame -b:a 64k -vsync 0 -f flv rtmp://ipofmynginxserver/myapp/mystream

  and

  raspivid -t 0 -w 1024 -h 768 -fps 25 -g 60 -vf -hf -b 1000000 -v -o temp.v & arecord -f cd -D plughw:0 | ffmpeg -r 25.37 -i temp.v -itsoffset 13.5 -i - -c:v copy -c:a libmp3lame -b:a 64k -vsync 0 -async 1 -f flv rtmp://ipofmynginxserver/myapp/mystream

  At first everything is fine (because of the offset) But after connection lost for 2-4 seconds audio and video starting to play asynchronus (audio first)
  I have tried to change options vsync and async but it didn’t make sense. If I’m trying to get alsa microphone with ffmpeg I’m getting alsa buffer xrun and it doesn’t work, the only way for me is to use raspivid and arecord, how can I solve my problem ? Thanks and sorry for my English.

• When recording MP4 using ffmpeg suddenly power off

  2 décembre 2016, par wanglx

  Now I used C language and ffmpeg realize a multiplex real-time audio and video to MP4 files of the program and everything works fine, but when in the process of reuse of sudden power failure, the recording is MP4 file is damaged, VLC can not play this file.
  I think reason is no call to write the trailer function av_write_trailer , causing index and time stamp information lost, I use araxis merge tool compared the successful call av_write_trailer function of file and a no av_write_trailer to call the damaged files and found two different points :
  1. Damaged files in the file header box number value not right
  2. The damaged file no end of file.

  Now I want to repair after power on my program can automatically repair the damaged files, in Google did not find effective methods.
  my train of thought is in the normal recording process saves per second a damaged file is missing two information : box number and end of file, save it to a local file, when writing the MP4 file integrity delete this file after, if power off damaged, then in the next power, read the file and the corresponding information to write the damaged files corresponding position to. But now the problem is that I don’t know how to save the number of box and the end of the file, I this is feasible ? If possible, what should I do ? Looking forward to your reply !