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• avformat/vobsub : fix several issues.

  29 septembre 2013, par Clément Bœsch

  avformat/vobsub : fix several issues.
  Here is an extract of fate-samples/sub/vobsub.idx, with an additional
  
  text at the end of each line to better identify each bitmap :
      timestamp : 00:04:55:445, filepos : 00001b000 Ace !
  
      timestamp : 00:05:00:049, filepos : 00001b800 Wake up, honey !
  
      timestamp : 00:05:02:018, filepos : 00001c800 I gotta go to work.
  
      timestamp : 00:05:02:035, filepos : 00001d000 < ???>
  
      timestamp : 00:05:04:203, filepos : 00001d800 Look after Clayton, okay ?
  
      timestamp : 00:05:05:947, filepos : 00001e800 I’ll be back tonight.
  
      timestamp : 00:05:07:957, filepos : 00001f800 Bye ! Love you.
  
      timestamp : 00:05:21:295, filepos : 000020800 Hey, Ace ! What’s up ?
  
      timestamp : 00:05:23:356, filepos : 000021800 Hey, how’s it going ?
  
      timestamp : 00:05:24:640, filepos : 000022800 Remember what today is ? The 3rd !
  
      timestamp : 00:05:27:193, filepos : 000023800 Look over there !
  
      timestamp : 00:05:28:369, filepos : 000024800 Where are they going ?
  
      timestamp : 00:05:28:361, filepos : 000025000 < ???>
  
      timestamp : 00:05:29:946, filepos : 000025800 Let’s go see.
  
      timestamp : 00:05:31:230, filepos : 000026000 I can’t, man. I got Clayton.
  Note the two "< ???>" : they are basically split subtitles (with the
  
  previous one), which the dvdsub decoder is now supposed to reconstruct
  
  with a previous commit. But also note that while the first chunk has
  
  increasing timestamps,
      timestamp : 00:05:02:018, filepos : 00001c800
  
      timestamp : 00:05:02:035, filepos : 00001d000
  ...it’s not the case of the second one (and this is not an exception in the
  
  original file) :
      timestamp : 00:05:28:369, filepos : 000024800
  
      timestamp : 00:05:28:361, filepos : 000025000
  For the dvdsub decoder, they need to be "filepos’ed" ordered, but the
  
  FFDemuxSubtitlesQueue is timestamps ordered, which is the reason of the
  
  introduction of a sub sort method in the context, to allow giving
  
  priority to the position, and then the timestamps. With that change, the
  
  dvdsub decoder get fed with ordered packets.
  Now the packet size estimation was also broken : the filepos differences
  
  in the vobsub index defines the full data read between two subtitles
  
  chunks, and it is necessary to take into account what is read by the
  
  mpegps_read_pes_header() function since the length returned by that
  
  function doesn’t count the size of the data it reads. This is fixed with
  
  the introduction of total_read, and old,new_pos. By doing this change,
  
  we can drop the unreliable len16 heuristic and simplify the whole loop.
  
  Note that mpegps_read_pes_header() often read more than one PES packet
  
  (typically in one call it can read 0x1ba and 0x1be chunk along with the
  
  relevant 0x1bd packet), which triggers the "total_read + pkt_size >
  
  psize" check. This is an expected behaviour, which could be avoided by
  
  having a more chunked version of mpegps_read_pes_header().
  The latest change is the extraction of each stream into its own
  
  subtitles queue. If we don’t do this, the maximum size for a subtitle
  
  chunk is broken, and the previous changes can not work. Having each
  
  stream in a different queue requires some little adjustments in the
  
  seek code of the demuxer.
  This commit is only meaningful as a whole change and can not be easily
  
  split. The FATE test changes because it uses the vobsub demuxer.
  

  • [DH] libavformat/mpeg.c
  • [DH] libavformat/subtitles.c
  • [DH] libavformat/subtitles.h
  • [DH] tests/ref/fate/sub2video

• v4l2 Repeating headers causing issues with FFmpeg

  11 septembre 2019, par AlexVestin

  I’m trying to stream from a raspberry pi using the python library aiortc with some modification to allow use the hardware encoding the rpi provides.

  The issue is if I the use v4l2 control repeat_sequence_header=0, the server is never sent any PPS or SPS at all, and is just sent nal unit types 1 and 5. So this makes the decoder on the server gives this error on every frame :

  failed to decode, skipping package: [Errno 1094995529] Invalid data found when processing input (16: h264)
  
  non-existing PPS 0 referenced
  
  decode_slice_header error
  
  no frame!

  However with repeat_sequence_header enabled the decoder complains on sending the SPS and PPS that the frame_num is resetting with

  Frame num change from 199 to 0
  
  decode_slice_header error

  So is there any way to tell the decoder that the frame_nums will be repeating, or to tell v4l2 to keep counting the frames up ?

• Issues implementing video Steganography using C# and ffmpeg [closed]

  25 juin 2012, par RAZER

  I'm trying to implement video steganography using c# and ffmpeg.
  The logic is as follows :

  -get bitmap frames from a video using ffmpeg argument
  (" -i d :\video.avi -r 25 d :\images\image-%5d.bmp")

  -hide data within lsb of bitmap data, starting from the first frames.

  -get video from the encode bitmap frames using ffmpeg argument
  (" -r 25 -i d :\images\image-%5d.bmp d :\out.avi")

  -now to decode hidden data, again get bitmap frames from above created video and perform decoding by
  extracting data from lsb of bitmap data.

  But the problem is the last step i cannot get the exact data that was hidden.
  I don't know what's go'in on, can anybody help me with the issue.