Newest 'ffmpeg' Questions - Stack Overflow

Les articles publiés sur le site

• Precise sample alignment of two identical audio files, which are shifted by few milliseconds using SoX / FFmpeg etc

  10 octobre 2016, par Vasyl Shumskyi

  I'm trying to achieve precise sample alignment of two identical audio files, which are shifted by few milliseconds without knowing the offset. Also the difference in the file duration are not the same as the samples shift. Can this be done with CLI audio tools SoX/FFmpeg or the likes?

• AVURLAsset tracks is empty, but video/audio is playable

  10 octobre 2016, par Paltr

  I have video that lives here:

  http://195.16.112.71/adaptive/66aebabb-2632-44fc-abf1-df29bca6b941.video/66aebabb-2632-44fc-abf1-df29bca6b941.m3u8
  

  Ffmpeg says that this video has 5 tracks and it's correctly.

  But if I use AVURLAsset with that link it says me that there isn't any tracks:

  NSArray* const tracks = asset.tracks; // it's empty
  

  I modified Apple's StichedStreamPlayer sample to reproduce this problem, it lies here: https://yadi.sk/d/hV3jfbx1Z9sfC

  Simply click 'Load Movie', than the 'Play' button - movie plays perfectly, but if you check tracks variable in prepareToPlayAsset function you find it's empty. The question is: why it's empty if in reality the video has 5 tracks and how this video could be playing if no tracks exist, as AVURLAsset says?

  Thanks for your help in advance!

• Extracting I frame in frame fraction range with ffmpeg

  10 octobre 2016, par Samuel

  I want to extract all the I frames, and then arrange the I frames according to all frame index. For example. There are 2997 frames in a video, and 200 I frames. I want to arrange the I frame in (1-300) into a folder. and I frames in (301-2997) to another folder.

  I know one solution that extract the I frames according to time range with -ss -t options. But some of my videos' frame rate is not integral. so sometimes it's not accurate depend on the time.

  So can I extract the I frames according to frame range(maybe called fraction of frame)

• What is the simplest way to get a video stream from a webcam as H.264 ?

  10 octobre 2016, par feuerstein

  The main requirement is that it is H.264 encoded video. I would prefer simpler solutions, even hacks, if the overhead is not excessively large (say ≥ 30ms). I don't want to use a framework that reads and decodes H.264 streams for me, because I need access to the encoded H.264 video data. These are my thoughts so far:

  • I've considered using ffmpeg as encoder and reading in the stream via UDP, but depacketizing and handling dropped packages might require some work.

  • Perhaps I could write the video stream to memory using tmpfs, however I want to be platform agnostic between Windows and Linux.

  • ffmpeg also has an option to write to a file to stdout, which however is line-based, so that might not be well suited for video data. I've read that there are ways to disable line-buffering when piping standard outputs, but I am not sure how reliable that is.

  • Another idea is to launch ffmpeg as a subprocess and access the output more directly in the RAM or perhaps continuously from the standard output without line-buffers (if that is possible).

  • Yet another option might be using libx264 directly, but that seems to be be more work than reading ffmpeg via UDP.

• Dose all H.264 video stream can be decompressed using Video Toolbox in iOS 8 ?

  10 octobre 2016, par fernandowei

  I met some h.264 video files which show large area of green on the screen without any error when decoding using Video Toolbox while I can decode most other h.264 video files successfully.