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• Http Live Streaming EXT-X-STREAM-INF, Calculating BANDWITH

  26 juin 2012, par Agzam

  Initially I've tried to find possible ways to do HLS segmenting on other non-Mac platforms.

  Segmenting videos for HLS involves the following steps :

  1) Splitting the encoded video into segments

  2) Creating playlist (.m3u8) file that simply contains list of segments for the current rendition, including duration in seconds for each segment

  3) Creating a variant playlist that contains relative paths to all playlists of all renditions with the information about BANDWITH which according to HTTP Live streaming protocol is :

  The value is a decimal-integer of bits per second. It MUST be an upper bound of the overall bitrate of each media segment (calculated to include container overhead) that appears or will appear in the Playlist.

  Latest version of ffmpeg includes possibilities of splitting videos. However ffmpeg can’t create m3u8 files. Creating simple playlist not a problem. But creating variant playlist might be :

  So variantplaylistcreator on Mac creates those, calculates somehow bitrates and puts value based on that into BANDWITH tag.

  I’ve tried many different ways but yet I couldn’t get exactly the same numbers that variantplaylistcreator does, and at this point I can’t find any information how exactly it calculates those values and what algorithm it uses.
  My numbers are close, but still slightly different.

  In theory it should not be a problem, but the point is - I don’t know that for sure.
  Maybe the BANDWITH information should be precise for flawless video playing, maybe it doesn’t have to.

  Anyway I'm really curious how exactly variantplaylistcreator calculates them :

• Android ffmpeg save and append h264 streamed videos

  8 octobre 2012, par Stefan Alexandru

  I need to save a video file generated by two video streams coming from two different sources. I'm using rtsp over tcp/ip, and the videos are encoded with h264.
  I need to first record the video from the first source and than continue with the second source.
  So what I tried was to declare two AVFormatContext instances, initialize both with avformat_open_input(&context, "rtsp://......",NULL,&options)
  and then read frames with av_read_frame(context,&packet)
  and write them in the video file av_write_frame(oc,&packet);
  It works fine saving the video from the first source, but if by example I saved y frames from the first context, when I try reading and saving the frames from the second context in the same file, for the first y frames I am tring to save, av_write_frame(oc,&packet2);
  would retun -22, and would not add the frame to the file.

  I think the problem is that the context variable remembers how many frames were read, and it gives every read packet an identification number, to make sure it isn't written twice. But when I'm using a new context those identification numbers reset, the AVOutputFormat or the AVFormatContext also retain the id of the package they are expecting to receive, and would not write anything until they receive a package with that id.
  Now I'm wondering how could I solve this inconvenience. I can't find any setter for that id, or any way to reuse the same context. I thought to modify the ffmpeg sources but they are pretty complex and I couldn't find what I was looking for.
  An alternative would be to save the two video in two different files but, I don't know how to append them afterwards, as ffmpeg can only append videos encoded with mpeg and rencoding the video isn't really an option, as it will take to much time. Also I couldn't find any other functional way to append two mp4 videos encoded with h264.

  I'll be happy to hear any kind of usable ideea to this problem.

• How to display image for particular time in a video using ffmpeg

  18 juin 2013, par Pratik Bhingardeve

  I am trying to created a video from the sequence of images. But i have to display each image with different numbers of seconds. How to do this with FFMPEG.

  Thanks in advance.