[FFmpeg-devel] libavutil/encryption_info: Allow multiple init info.

[Jacob Trimble]

On Tue, May 8, 2018 at 3:47 PM, Michael Niedermayer
<michael at niedermayer.cc> wrote:
> On Mon, May 07, 2018 at 04:59:33PM -0700, Jacob Trimble wrote:
>> On Mon, May 7, 2018 at 3:18 PM, Michael Niedermayer
>> <michael at niedermayer.cc> wrote:
>> > On Mon, Apr 23, 2018 at 11:03:57AM -0700, Jacob Trimble wrote:
>> >> While integrating my encryption info changes, I noticed a problem with
>> >> the init info structs.  I implemented them as side-data on the Stream.
>> >> But this means there can only be one per stream.  However, there can
>> >> be multiple 'pssh' atoms in a single stream (e.g. for key rotation or
>> >> multiple key systems). (sorry for not noticing sooner)
>> >>
>> >> Attached is a patch to fix this by making the init info a
>> >> singly-linked-list.  It is ABI compatible and is still easy to use and
>> >> understand.  The alternative would be to break ABI and have the
>> >> side-data methods return an array of pointers.  I could do that
>> >> instead if that is preferable.
>> >
>> >>  encryption_info.c |  154 +++++++++++++++++++++++++++++++++++-------------------
>> >>  encryption_info.h |    5 +
>> >>  2 files changed, 106 insertions(+), 53 deletions(-)
>> >> e5eecc73a6997bbd11541771372d38ea9c3972a7  0001-libavutil-encryption_info-Allow-multiple-init-info.patch
>> >> From bb941a77e882e93629d63d63059d0063b9519e29 Mon Sep 17 00:00:00 2001
>> >> From: Jacob Trimble <modmaker at google.com>
>> >> Date: Mon, 23 Apr 2018 10:33:58 -0700
>> >> Subject: [PATCH] libavutil/encryption_info: Allow multiple init info.
>> >>
>> >> It is possible for there to be multiple encryption init info structure.
>> >> For example, to support multiple key systems or in key rotation.  This
>> >> changes the AVEncryptionInitInfo struct to be a linked list so there
>> >> can be multiple structs without breaking ABI.
>> >>
>> >> Signed-off-by: Jacob Trimble <modmaker at google.com>
>> >> ---
>> >>  libavutil/encryption_info.c | 154 +++++++++++++++++++++++-------------
>> >>  libavutil/encryption_info.h |   5 ++
>> >>  2 files changed, 106 insertions(+), 53 deletions(-)
>> >>
>> >> diff --git a/libavutil/encryption_info.c b/libavutil/encryption_info.c
>> >> index 20a752d6b4..9935c10d74 100644
>> >> --- a/libavutil/encryption_info.c
>> >> +++ b/libavutil/encryption_info.c
>> >> @@ -160,13 +160,16 @@ uint8_t *av_encryption_info_add_side_data(const AVEncryptionInfo *info, size_t *
>> >>  }
>> >>
>> >>  // The format of the AVEncryptionInitInfo side data:
>> >> -// u32be system_id_size
>> >> -// u32be num_key_ids
>> >> -// u32be key_id_size
>> >> -// u32be data_size
>> >> -// u8[system_id_size] system_id
>> >> -// u8[key_id_size][num_key_id] key_ids
>> >> -// u8[data_size] data
>> >> +// u32be init_info_count
>> >> +// {
>> >> +//   u32be system_id_size
>> >> +//   u32be num_key_ids
>> >> +//   u32be key_id_size
>> >> +//   u32be data_size
>> >> +//   u8[system_id_size] system_id
>> >> +//   u8[key_id_size][num_key_id] key_ids
>> >> +//   u8[data_size] data
>> >> +// }[init_info_count]
>> >>
>> >>  #define FF_ENCRYPTION_INIT_INFO_EXTRA 16
>> >>
>> >> @@ -215,6 +218,7 @@ void av_encryption_init_info_free(AVEncryptionInitInfo *info)
>> >>          for (i = 0; i < info->num_key_ids; i++) {
>> >>              av_free(info->key_ids[i]);
>> >>          }
>> >> +        av_encryption_init_info_free(info->next);
>> >>          av_free(info->system_id);
>> >>          av_free(info->key_ids);
>> >>          av_free(info->data);
>> >> @@ -225,71 +229,115 @@ void av_encryption_init_info_free(AVEncryptionInitInfo *info)
>> >>  AVEncryptionInitInfo *av_encryption_init_info_get_side_data(
>> >>      const uint8_t *side_data, size_t side_data_size)
>> >>  {
>> >> -    AVEncryptionInitInfo *info;
>> >> +    AVEncryptionInitInfo *ret = NULL, *info;
>> >>      uint64_t system_id_size, num_key_ids, key_id_size, data_size, i;
>> >> +    uint64_t init_info_count;
>> >>
>> >> -    if (!side_data || side_data_size < FF_ENCRYPTION_INIT_INFO_EXTRA)
>> >> -        return NULL;
>> >> -
>> >> -    system_id_size = AV_RB32(side_data);
>> > [...]
>> >> +    init_info_count = AV_RB32(side_data);
>> >
>> > i may be missing something but this looks like the meaning of the first
>> > field changes, this thus doesnt look compatible to me
>>
>> It changes the binary format of the side-data, but that was explicitly
>> not part of ABI.  The fields in the structs are unchanged.  This would
>> only cause a problem if the side data bytes were stored out-of-band
>> from a different version of FFmpeg.
>
> yes, right.
> its side data that is neighter a C struct nor a well defined byte stream
> its a opaque block that can only be passed to libavutil which then translates
> it into a C struct.
> its not new but it still feels clumsy to use this as means to pass data around
>

I know it's weird, but this was the design that was decided on when
this was added.  Are there any changes you want for this patch?

>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> If you think the mosad wants you dead since a long time then you are either
> wrong or dead since a long time.
>
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