[FFmpeg-trac] #4016(avformat:new): DRM protected content should be detected

[FFmpeg]

#4016: DRM protected content should be detected
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             Reporter:  hendrik   |                     Type:  enhancement
               Status:  new       |                 Priority:  normal
            Component:  avformat  |                  Version:  2.4.2
             Keywords:  DRM m4p   |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
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 AFAIK FFmpeg libraries contain no special code to recognize whether a file
 has been DRM protected e.g. by Apple's so-called "FairPlay". mp4 files are
 decoded and played - but the result is simply garbage.

 It would be nice, if it was possible to detect whether a file is protected
 or not.
 Please note, that I don't mean to suggest building a decoder (like
 ticket:1800). Instead, just knowing that we simply cannot decode a file
 properly is already valuable.

 A possible implementation could be for `avcodec_decode_audio4(...)` to
 return an appropriate error code, if the packet is encrypted and therefore
 cannot be decoded properly.

 For `.m4p` this is not hard to detect. It contains an atom called `drms`.
 If it is present, the file cannot be properly decoded. For WMA there seems
 to be also some sort of mechanism (see e.g. https://mail.kde.org/pipermail
 /taglib-devel/2011-March/001885.html).

 Further resources for m4p are:

 * http://atomicparsley.sourceforge.net/mpeg-4files.html
 *
 http://www.cs.sjsu.edu/faculty/stamp/students/RamyaVenkataramu_CS298Report.pdf

 To illustrate where to find the `drms` atom, here's an excerpt generated
 with AtomicParsely:

 {{{
 > AtomicParsley.exe test.m4p -T +
 Atom ftyp @ 0 of size: 32, ends @ 32
 Atom moov @ 32 of size: 98194, ends @ 98226
      Atom mvhd @ 40 of size: 108, ends @ 148
      Atom trak @ 148 of size: 39374, ends @ 39522
          Atom tkhd @ 156 of size: 92, ends @ 248
          Atom edts @ 248 of size: 36, ends @ 284
              Atom elst @ 256 of size: 28, ends @ 284
          Atom mdia @ 284 of size: 39238, ends @ 39522
              Atom mdhd @ 292 of size: 32, ends @ 324
              Atom hdlr @ 324 of size: 58, ends @ 382
              Atom minf @ 382 of size: 39140, ends @ 39522
                  Atom smhd @ 390 of size: 16, ends @ 406
                  Atom hdlr @ 406 of size: 57, ends @ 463
                  Atom dinf @ 463 of size: 36, ends @ 499
                      Atom dref @ 471 of size: 28, ends @ 499
                  Atom stbl @ 499 of size: 39023, ends @ 39522
                      Atom stsd @ 507 of size: 999, ends @ 1506
                          Atom drms @ 523 of size: 983, ends @ 1506
                              Atom esds @ 559 of size: 51, ends @ 610
                              Atom sinf @ 610 of size: 896, ends @ 1506
                                  Atom frma @ 618 of size: 12, ends @ 630
                                  Atom schm @ 630 of size: 20, ends @ 650
                                  Atom schi @ 650 of size: 856, ends @ 1506
                                      Atom user @ 658 of size: 12, ends @
 670
                                      Atom key  @ 670 of size: 12, ends @
 682
                                      Atom iviv @ 682 of size: 24, ends @
 706
                                      Atom righ @ 706 of size: 88, ends @
 794
                                      Atom name @ 794 of size: 264, ends @
 1058
                                      Atom priv @ 1058 of size: 448, ends @
 1506
                      Atom stts @ 1506 of size: 24, ends @ 1530
                      Atom stsc @ 1530 of size: 7756, ends @ 9286
                      Atom stsz @ 9286 of size: 27640, ends @ 36926
                      Atom stco @ 36926 of size: 2596, ends @ 39522
      Atom udta @ 39522 of size: 58704, ends @ 98226
          Atom meta @ 39530 of size: 58696, ends @ 98226
 [...]
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/4016>
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