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• Encoding H.264 CBR videos with FFmpeg

  27 août 2015, par Cornstalks

  I’m trying to encode a video with ffmpeg into H.264 (via the libx264 library) with a constant bit rate. I know, I know, VBR is often preferred, but for this specific job I’m required to use CBR (just as long as it’s so many kilobytes per second ; it doesn’t have to be an exact kilobytes per frame, afaik). My sample video I’m using to test is from here : http://a1408.g.akamai.net/5/1408/1388/2005110403/1a1a1ad948be278cff2d96046ad90768d848b41947aa1986/sample_iTunes.mov.zip (it comes from http://support.apple.com/kb/HT1425)

  I can get a constant bit rate when encoding the video with MPEG-4 Video (using the commands ffmpeg -i sample_iTunes.mov -b 819968 -minrate 819968 -maxrate 819968 out.mov), and the bit rate is as expected. Reading the video’s specs via the QuickTime Inspector, it’s got a data rate of 844.94 kbit/s. Cool.

  However, when I change the codec to libx264, it seems to completely ignore my bitrate requests ! The command I’m trying is "ffmpeg -i sample_iTunes.mov -vcodec libx264 -vpre medium -b 819968 -vb 819968 -minrate 819968 -maxrate 819968 -bufsize 400000 test.mov". But when I check the video’s specs via the QuickTime Inspector, it’s got a data rate of 254.74 kbit/s. WTF ? That’s not even close !

  I’ve tried changing so many parameters and adding tons of different things, and I’ve spent 2 days googling this, but I can’t seem to get it to work. If I encode the video with the MainConcept H.264 encoder, I can get a constant bitrate, but I need this to work with ffmpeg.

  If someone can help me figure out how to do CBR H.264 encoding with FFmpeg, I will love you forever !

• Live Stream using .m3u8 and .ts files with iPhone as server

  26 février 2015, par Bhumit

  I am trying to accomplish a task to live stream from iPhone camera. I have done some research and found that i can use .m3u8 files for streaming live video with should contain .ts(Mpeg-2) files .

  Now the file which i have on my iPhone is .mp4 file and it does not work with .m3u8, so i figured out i will have to convert .mp4 to .ts for that , but i have not succeeded in doing so.

  I found that it is possible to convert video ffmpeg lib as mentioned in this article here. I have successfully imported ffmpeg library but not able figure out how can i use it to convert a video as i am using this for first time.

  One another thing apple documentation says

  There are a number of hardware and software encoders that can create
  MPEG-2 transport streams carrying MPEG-4 video and AAC audio in real
  time.

  What is being said here ? is there any other way i can use .mp4 files for live streaming without converting them from iOS ?

  Let me know if i am not clear, i can provide more information .Any suggestion is appreciated. I would like to know am i on a right path here ?

  EDIT

  I am adding more info to my question, so basically what i am asking is , we can convert .mp4 video to .ts using following command

  ffmpeg -i file.mp4 -acodec libfaac -vcodec libx264 -an -map 0 -f segment -segment_time 10 -segment_list test.m3u8 -segment_format mpegts -vbsf h264_mp4toannexb -flags -global_header stream%05d.ts

  How can i use ffmpeg library to do what this command does in iOS.

• Ramp- Slow Motion in IOS

  26 juin 2013, par 2vision2

  I have to do "ramp-slow motion" in a video file along with audio, in-between some frames and need to store the ramped video as a new video.

  Ref : http://www.youtube.com/watch?v=BJ3_xMGzauk (watch from 0 to 10s)

  From my analysis, I've found that AVFoundation framework can be helpful.

  Ref :
  http://developer.apple.com/library/ios/#documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/00_Introduction.html

  Copy and pasted from the above link :

  "
  Editing
  AV Foundation uses compositions to create new assets from existing pieces of media (typically, one or more video and audio tracks). You use a mutable composition to add and remove tracks, and adjust their temporal orderings. You can also set the relative volumes and ramping of audio tracks ; and set the opacity, and opacity ramps, of video tracks. A composition is an assemblage of pieces of media held in memory. When you export a composition using an export session, it's collapsed to a file.
  On iOS 4.1 and later, you can also create an asset from media such as sample buffers or still images using an asset writer.

  "

  Questions :
  Can I "ramp-slow mote" the video/audio file using the AVFoundation framework ? Or Is there any other package available ? If i want to handle audio and video separately, please guide me how to do ?