[NUT-devel] [PATCH] nut: Add per frame sidedata and metadata

[Luca Barbato]

On 27/03/13 15:41, Michael Niedermayer wrote:
>  reserved_count[frame_code] (v)
> -    MUST be <256.
> +    Muxers conforming to this version of the specification MUST set it to
> +    !!(flags[frame_code] & FLAG_SIDEDATA)
> +    Demuxers MUST support any value from 0 to 255
> +    These rules are to ensure extensibility of the format.

Would enjoy a better explanation.
Such as "muxer supporting FLAG_SIDEDATA MUST set the reserved_count to 1
if side data is in used in order to be compatible with older demuxers"

> +
> +sidedata_size[frame_code] (v)
> +    Size in bytes at the end inside data which represent frame sidedata and
> +    frame metadata.

metadata and sidedata are different items, I'm not exactly cool in
lumping everything in the same serialized dictionary.

> +
> +side_data
> +    This data structure is used both in frames for per frame side and metadata
> +    as well as info tags for metadata covering the whole file, a stream
> +    chapter or other.
> +    Metadata is data that is about the actual data and generally not essential
> +    for correct presentation
> +    Sidedata is semantically part of the data and essential for its correct
> +    presentation. The same syntax is used by both for simplicity.
> +    The use of sidedata should be avoided and the information be put inside
> +    the codec bitstream, if its syntax supports carrying such information.

This statement should be omitted.

> +    Types of per frame side data:
> +    "Channels", "ChannelLayout", "SampleRate", "Width", "Height"
> +        This frame changes the number of channels, the channel layout, ... to
> +        the given value (v)
> +        If used in any frame of a stream then every keyframe of the stream
> +        SHOULD carry such sidedata to allow seeking.
> +    "Extradata", "Palette"
> +        This frame changes the codec_specific_data or palette to the given
> +        value (vb)
> +        If used in any frame of a stream then every keyframe of the stream
> +        SHOULD carry such sidedata to allow seeking.
> +    "CodecSpecificSide<num>"
> +        Codec specific side data, equivalent to matroskas BlockAdditional (vb)
> +        the "<num>" should be replaced by a number identifying the type of
> +        side data, it is equivalent/equal to BlockAddId in matroska.
> +    "SkipStart", "SkipEnd"
> +        The decoder should skip/drop the specified number of samples at the
> +        start/end of this frame (v)
> +    "UserData<identifer here>"
> +        User specific side data, the "<identifer here>" should be replaced
> +        by a globally unique identifer of the project that
> +        uses/creates/understands the side data. For example "UserDataFFmpeg"

I'm not certain serializing type and enumeration this way would work
that well.

lu