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• checkasm : use perf API on Linux ARM*

  1er septembre 2017, par Clément Bœsch

  checkasm : use perf API on Linux ARM*
  On ARM platforms, accessing the PMU registers requires special user
  
  access permissions. Since there is no other way to get accurate timers,
  
  the current implementation of timers in FFmpeg rely on these registers.
  
  Unfortunately, enabling user access to these registers on Linux is not
  
  trivial, and generally involve compiling a random and unreliable github
  
  kernel module, or patching somehow your kernel.
  Such module is very unlikely to reach the upstream anytime soon. Quoting
  
  Robin Murphin from ARM :
  > Say you do give userspace direct access to the PMU ; now run two or more
  
  > programs at once that believe they can use the counters for their own
  
  > "minimal-overhead" profiling. Have fun interpreting those results...
  
  >
  
  > And that's not even getting into the implications of scheduling across
  
  > different CPUs, CPUidle, etc. where the PMU state is completely beyond
  
  > userspace's control. In general, the plan to provide userspace with
  
  > something which might happen to just about work in a few corner cases,
  
  > but is meaningless, misleading or downright broken in all others, is to
  
  > never do so.
  As a result, the alternative is to use the Performance Monitoring Linux
  
  API which makes use of these registers internally (assuming the PMU of
  
  your ARM board is supported in the kernel, which is definitely not a
  
  given...).
  While the Linux API is obviously cross platform, it does have a
  
  significant overhead which needs to be taken into account. As a result,
  
  that mode is only weakly enabled on ARM platforms exclusively.
  Note on the non flexibility of the implementation : the timers (native
  
  FFmpeg vs Linux API) are selected at compilation time to prevent the
  
  need of function calls, which would result in a negative impact on the
  
  cycle counters.
  

  • [DH] configure
  • [DH] tests/checkasm/checkasm.c
  • [DH] tests/checkasm/checkasm.h

• mpegvideo : Expand macro

  10 juin 2015, par Vittorio Giovara

  mpegvideo : Expand macro
  Having this macro in an header only facilitates the use of such header.
  
  The code increase is minimal and files have one less dependency
  
  on mpegvideo.h.
  

  • [DBH] libavcodec/flvenc.c
  • [DBH] libavcodec/h261enc.c
  • [DBH] libavcodec/mpegvideo.h
  • [DBH] libavcodec/mpegvideo_enc.c
  • [DBH] libavcodec/rv10enc.c
  • [DBH] libavcodec/rv20enc.c

• avformat/mpegts : parse sections with multiple tables

  9 mai 2018, par Aman Gupta

  avformat/mpegts : parse sections with multiple tables
  Fixes PMT parsing in some mpegts streams which contain
  
  multiple tables within the PMT pid. Previously, the parser
  
  assumed only one table was present in each packet, and discarded
  
  the rest of the section data after attempting to parse the first
  
  table.
  A similar issue was documented in the BeyondTV software[1], which
  
  helped me diagnose the same bug in the ffmpeg mpegts demuxer. I also
  
  tried DVBInspector, libdvbpsi's dvbinfo, and tstools' tsinfo to
  
  help debug. The former two properly read PMTs with multiple tables,
  
  whereas the last has the same bug as ffmpeg.
  I've created a minimal sample[2] which contains the combined PMT.
  
  Here's what ffmpeg probe shows before and after this patch :
  Before :
      Input #0, mpegts, from 'combined-pmt-tids.ts' :
  
        Duration : 00:00:01.08, start : 4932.966167, bitrate : 741 kb/s
  
        Program 1
  
        No Program
  
          Stream #0:0[0xf9d] : Audio : ac3, 48000 Hz, mono, fltp, 96 kb/s
  
          Stream #0:1[0xf9b] : Audio : mp3, 0 channels, fltp
  
          Stream #0:2[0xf9c] : Unknown : none
  After :
      Input #0, mpegts, from 'combined-pmt-tids.ts' :
  
        Duration : 00:00:01.11, start : 4932.966167, bitrate : 718 kb/s
  
        Program 1
  
          Stream #0:0[0xf9b] : Video : mpeg2video ([2][0][0][0] / 0x0002), none(tv, top first), 29.97 fps, 29.97 tbr, 90k tbn, 90k tbc
  
          Stream #0:1[0xf9c](eng) : Audio : ac3 (AC-3 / 0x332D4341), 48000 Hz, 5.1(side), fltp, 384 kb/s
  
          Stream #0:2[0xf9d](spa) : Audio : ac3 (AC-3 / 0x332D4341), 48000 Hz, mono, fltp, 96 kb/s
  With the patch, the PMT is parsed correctly so the streams are
  
  created in the correct order, are associated with "Program 1",
  
  and their codecs are set correctly.
  [1] http://forums.snapstream.com/vb/showpost.php?p=343816&postcount=201
  
  [2] https://s3.amazonaws.com/tmm1/combined-pmt-tids.ts
  Signed-off-by : Aman Gupta <aman@tmm1.net>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/mpegts.c