[FFmpeg-devel] [RFC] avcodec/avcodec.h: Add encryption info side data

[wm4]

On Fri, 15 Dec 2017 14:24:17 -0800
Jacob Trimble <modmaker-at-google.com at ffmpeg.org> wrote:

> From a1b2cbcb7da4da69685f8f1299b70b672ce448e3 Mon Sep 17 00:00:00 2001
> From: Jacob Trimble <modmaker at google.com>
> Date: Tue, 5 Dec 2017 14:52:22 -0800
> Subject: [PATCH] avcodec/avcodec.h: Add encryption info side data.
> 
> This new side-data will contain info on how a packet is encrypted.
> This allows the app to handle packet decryption.  To allow for a
> variable number of subsamples, the buffer for the side-data will be
> allocated to hold both the structure and the array of subsamples.  So
> the |subsamples| member will point to right after the struct.
> 
> Signed-off-by: Jacob Trimble <modmaker at google.com>
> ---
>  libavcodec/avcodec.h | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 70 insertions(+)
> 
> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> index 5db6a81320..ccc89345e8 100644
> --- a/libavcodec/avcodec.h
> +++ b/libavcodec/avcodec.h
> @@ -1112,6 +1112,63 @@ typedef struct AVCPBProperties {
>      uint64_t vbv_delay;
>  } AVCPBProperties;
>  
> +typedef struct AVPacketSubsampleEncryptionInfo {
> +    /** The number of bytes that are clear. */
> +    unsigned int bytes_of_clear_data;
> +
> +    /**
> +     * The number of bytes that are protected.  If using pattern encryption,
> +     * the pattern applies to only the protected bytes; if not using pattern
> +     * encryption, all these bytes are encrypted.
> +     */
> +    unsigned int bytes_of_protected_data;
> +} AVPacketSubsampleEncryptionInfo;
> +
> +/**
> + * This describes encryption info for a packet.  This contains frame-specific
> + * info for how to decrypt the packet before passing it to the decoder.  If this
> + * side-data is present, then the packet is encrypted.
> + */
> +typedef struct AVPacketEncryptionInfo {
> +    /** The fourcc encryption scheme. */
> +    uint32_t scheme;
> +
> +    /** The ID of the key used to encrypt the packet. */
> +    uint8_t key_id[16];
> +
> +    /** The initialization vector. */
> +    uint8_t iv[16];
> +
> +    /**
> +     * Only used for pattern encryption.  This is the number of 16-byte blocks
> +     * that are encrypted.
> +     */
> +    unsigned int crypt_byte_block;
> +
> +    /**
> +     * Only used for pattern encryption.  This is the number of 16-byte blocks
> +     * that are clear.
> +     */
> +    unsigned int skip_byte_block;
> +
> +    /**
> +     * The number of sub-samples in this packet.  If 0, then the whole sample
> +     * is encrypted.
> +     */
> +    unsigned int subsample_count;
> +
> +    /** The subsample encryption info. */
> +    AVPacketSubsampleEncryptionInfo *subsamples;

I don't think this is sane. So far, side data could simply be copied
with memcpy, and having pointers to non-static data in side data would
break this completely.

> +} AVPacketEncryptionInfo;
> +/**
> + * The size of the side-data for the AV_PKT_DATA_PACKET_ENCRYPTION_INFO type.
> + * The side-data will contain the AVPacketEncryptionInfo struct followed by
> + * the subsample array.  The subsamples member should point to after the struct
> + * so the app can easily access it.
> + */
> +#define FF_PACKET_ENCRYPTION_INFO_SIZE(subsample_count) \
> +    (sizeof(AVPacketEncryptionInfo) + sizeof(AVPacketSubsampleEncryptionInfo) * subsample_count)
> +
>  /**
>   * The decoder will keep a reference to the frame and may reuse it later.
>   */
> @@ -1327,6 +1384,19 @@ enum AVPacketSideDataType {
>       */
>      AV_PKT_DATA_A53_CC,
>  
> +    /**
> +     * This side data is encryption "initialization data".
> +     * For MP4 this is the entire 'pssh' box.
> +     * For WebM this is the key ID.
> +     */
> +    AV_PKT_DATA_ENCRYPTION_INIT_DATA,
> +
> +    /**
> +     * This side data is an AVPacketEncryptionInfo structure and contains info
> +     * about how the packet is encrypted.
> +     */
> +    AV_PKT_DATA_PACKET_ENCRYPTION_INFO,
> +
>      /**
>       * The number of side data types.
>       * This is not part of the public API/ABI in the sense that it may