MP4中HEVC解码配置记录详解与FFmpeg结合分析

Draft Specification for HEVC/H.265 elementary streams in Matroska:

CodecID: V_MPEGH/ISO/HEVC

General Limitations Regarding SimpleBlock Usage:
(TODO: Similar area for Block usage?)

* Each NAL unit shall be written with the start code stripped, and
prefixed by an unsigned big endian integer that contains the length of
the given NAL unit in bytes. The size of this prefix in bytes shall be
set by the value of the lengthSizeMinusOne field plus 1 of the
currently active CodecPrivate structure (the available sizes are 1, 2
and 4 bytes).

* A SimpleBlock shall contain one or more VCL NAL units that make up a
single picture (be it a field or a frame), as well as possible other
NAL units depending on the limitations imposed upon the stream by the
CodecPrivate structure.

* The 'keyframe' (random access point) flag shall only be set when the
following conditions are satisfied:

- The contained VCL NAL unit(s) signal an IRAP picture as defined in
ISO/IEC 23008-2 and ITU-T Recommendation H.265.

- The contained VCL NAL unit(s) and all the following VCL NAL units in
coding order can be correctly decoded by feeding the decoder the
parameter sets included in the related CodecPrivate structure, and, in
case the CodecPrivate structure permits, all the possible parameter
sets included in the SimpleBlock as well as all the following

SimpleBlocks.

* The 'invisible' flag shall be set if the picture is a non-displayed
reference picture.

Contents of CodecPrivate:

Generally follows the definition of HEVCDecoderConfigurationRecord in
ISO/IEC 14496-15, but until the 3rd edition of 14496-15 gets
officially finalized, the version entry (configurationVersion) shall
be written as 0 (zero), not 1 (one) as 14496-15 defines it.

After the official release of 14496-15, 3rd ed., the extradata format
can be checked and possibly updated, and the configurationVersion can
finally be bumped to to match the 14496-15 specification.

A reader must not attempt attempt to decode this record or the
stream(s) to which it applies if the version number is unrecognised.
Compatible extensions to this record will not change the configuration
version code, and readers should be prepared to ignore unrecognised
data beyond the definition of the data they understand.

As the 14496-15 specification defines the implicit default value for
array_completeness depending on the ID of the stream, this Matroska
mapping shall define the implicit default as 0.

Since this is a bit-based document, all values are left-most bit
first, and thus big endian if they take more than one byte of space.
All fields that contain straight-out copies of HEVC data shall of
course follow ISO/IEC 23008-2 and ITU-T Recommendation H.265.