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• mpeg2_metadata, cbs_mpeg2 : Fix handling of colour_description

  20 juin 2019, par Andreas Rheinhardt

  mpeg2_metadata, cbs_mpeg2 : Fix handling of colour_description
  If a sequence display extension is read with colour_description equal to
  
  zero, but a user wants to add one or more of the colour_description
  
  elements, then the colour_description elements the user did not explicitly
  
  request to be set are set to zero and not to the value equal to
  
  unknown/unspecified (namely 2). A value of zero is not only inappropriate,
  
  but explicitly forbidden. This is fixed by inferring the right default
  
  values during the reading process if the elements are absent ; moreover,
  
  changing any of the colour_description elements to zero is now no longer
  
  possible.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/cbs_mpeg2.c
  • [DH] libavcodec/cbs_mpeg2_syntax_template.c
  • [DH] libavcodec/mpeg2_metadata_bsf.c

• cbs_mpeg2 : Fix parsing of picture and slice headers

  20 juin 2019, par Andreas Rheinhardt

  cbs_mpeg2 : Fix parsing of picture and slice headers
  1. The extra information in slice headers was parsed incorrectly :
  
  In the first reading pass to derive the length of the extra information,
  
  one should look at bits n, n + 9, n + 18, ... and check whether they
  
  equal one (further extra information) or zero (end of extra information),
  
  but instead bits n, n + 8, n + 16, ... were inspected. The second pass
  
  of reading (where the length is already known and the bytes between the
  
  length-determining bits are copied into a buffer) did not record what
  
  was in bits n, n + 9, n + 18, ..., presuming they equal one. And during
  
  writing, the bytes in the buffer are interleaved with set bits and
  
  written. This means that if the detected length of the extra information
  
  was greater than the real length, the output was corrupted. Fortunately
  
  no sample is known that made use of this mechanism : The extra information
  
  in slices is still marked as reserved in the specifications. cbs_mpeg2
  
  is now ready in case this changes.
  2. Furthermore, the buffer is now padded and slightly different, but
  
  very similar code for reading resp. writing has been replaced by code
  
  used for both. This was made possible by a new macro, the equivalent
  
  to cbs_h2645's fixed().
  3. These changes also made it possible to remove the extra_bit_slice
  
  element from the MPEG2RawSliceHeader structure. Said element was always
  
  zero except when the detected length of the extra information was less
  
  than the real length.
  4. The extra information in picture headers (which uses essentially the
  
  same syntax as the extra information in slice headers) has simply been
  
  forgotten. This meant that if this extra information was present, it was
  
  discarded during reading ; and unfortunately writing created invalid
  
  bitstreams in this case (an extra_bit_picture - the last set bit of the
  
  whole unit - indicated that there would be a further byte of data,
  
  although the output didn't contain said data).
  This has been fixed ; both types of extra information are now parsed via
  
  the same code and essentially passed through.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/cbs_mpeg2.c
  • [DH] libavcodec/cbs_mpeg2.h
  • [DH] libavcodec/cbs_mpeg2_syntax_template.c

• Splitting video with ffmpeg gives weird output

  5 août 2019, par PyStraw45

  I want to split a video into (mostly) equal parts of 120sec length. The code below works but only the first video output is of normal mp4 format. The others seem like they start at where the previous video ends but only like the video file was never cut

  First video timeline image :

  

  next video timeline, as you can see it starts at 2min mark rather than at 0 as a separate video. Even though the file stats still show the video as being 2 minutes in length :

  

  ffmpeg -i 1146redmp4.mp4 -c:v libx264 -crf 22 -map 0 -segment_time 120 -g 120 -sc_threshold 0 -force_key_frames "expr:gte(t,n_forced*120)" -f segment 1146output%03d.mp4

  If this is the correct output and not a bug. How do I have the video splits be output as their own video ?