How HEVC/H.265 works, technical details & diagrams

[KarthikTdk]

How entropy works in HEVC, like input is output of Quantization, like how this data converts into bins how it varies to each value and output is constant ?

[LigH]

The entropy coding in HEVC is CABAC = Context-adaptive binary arithmetic coding, a specific variant of the general Arithmetic coding.

For more details, you may need to be able to read the source code.

[KarthikTdk]

Basically we have 3 frames in hevc, I, P, B frames
Initially it take 1st frames as I FRAME , and next p or b
Is this right?
And please tell me order of frame execution and is b frame is supported
And where can get source code of HEVC.
Thank you 🙏.

[LigH]

Yes, B frames are supported.
I frames exist in two variants: IDR (Intraframe with Decoder Reset) to start a GOP, and intermediate Intraframes for single frames with very different content compared to surrounding frames, so the decoding of P and B frames may skip that one (but they are displayed, just not referenced by other frames)
Reference sources: https://vcgit.hhi.fraunhofer.de/jvet/HM
Reference documents: https://hevc.hhi.fraunhofer.de/

[benwaggoner]

Originally Posted by KarthikTdk

Basically we have 3 frames in hevc, I, P, B frames
Initially it take 1st frames as I FRAME , and next p or b
Is this right?
And please tell me order of frame execution and is b frame is supported
And where can get source code of HEVC.
Thank you 🙏.

We also have Reference B-frames and non-reference b-frames.

And the new x265 version supports multiple hierarchies of B-frames.

[KarthikTdk]

Thanks you for replying @benwaggoner and LigH and
Can i get source code in verilog Or c languages
Thank you!

[KarthikTdk]

After I frame done we go with p and b frame after that again I FRAME will come again?
If it will come then when like at which conditions!
Thank you!

[rwill]

@KarthikTdk: I think you are way in over your head.

[lvqcl]

Originally Posted by KarthikTdk

Basically I am working on this protocol

What protocol?

[KarthikTdk]

Originally Posted by lvqcl

what protocol?

h265/hevc

[LigH]

Originally Posted by KarthikTdk

Can i get source code in verilog Or c languages

I already posted you the link to "Reference sources" at Fraunhofer, they are in C/C++.

And highly optimized and enhanced sources for the x265 encoder in C/C++ and Assembler are available from Multicoreware's Bitbucket; more info at https://www.x265.org/

[benwaggoner]

Originally Posted by LigH

And highly optimized and enhanced sources for the x265 encoder in C/C++ and Assembler are available from Multicoreware's Bitbucket; more info at https://www.x265.org/

And for practical performance, you'll want to be using a version optimized for a given architecture with lots of SIMD usage. ARM and x86 performance are nearly equivalent these days, and there's some decent POWER support as well.

The reference encoders is, charitably, glacially slow.

[KarthikTdk]

Hi there,
How to identify 1st frame and last frame in H265
Thank you in advance.

[Emulgator]

Run an indexer on the file, like LWLibavVideoSource.
A .lwi file is generated. It tells the offsets of all frames.
An example:
Index=0,POS=0,PTS=-9223372036854775808,DTS=-9223372036854775808,EDI=0
Key=1,Pic=1,POC=0,Repeat=1,Field=0
Index=0,POS=49499,PTS=-9223372036854775808,DTS=-9223372036854775808,EDI=0
Key=0,Pic=2,POC=4,Repeat=1,Field=0
until
Index=0,POS=23035292,PTS=-9223372036854775808,DTS=-9223372036854775808,EDI=0
Key=0,Pic=3,POC=1731,Repeat=1,Field=0

The last frame: You want to look for ....POS=23035292

Example file size was 21,9 MB (23.048.192 Bytes)

[KarthikTdk]

Originally Posted by Emulgator

Run an indexer on the file, like LWLibavVideoSource.
A .lwi file is generated. It tells the offsets of all frames.
An example:
Index=0,POS=0,PTS=-9223372036854775808,DTS=-9223372036854775808,EDI=0
Key=1,Pic=1,POC=0,Repeat=1,Field=0
Index=0,POS=49499,PTS=-9223372036854775808,DTS=-9223372036854775808,EDI=0
Key=0,Pic=2,POC=4,Repeat=1,Field=0
until
Index=0,POS=23035292,PTS=-9223372036854775808,DTS=-9223372036854775808,EDI=0
Key=0,Pic=3,POC=1731,Repeat=1,Field=0

The last frame: You want to look for ....POS=23035292

Example file size was 21,9 MB (23.048.192 Bytes)

Hi thanks for explaining
Can u tell me again, I didn't get.

[LigH]

You do not analyse the video stream yourself. You let a smart indexer containing decades of experience do that and then parse the index file it created.

Indexing a media file with MPEG HEVC video is quite complex. It depends at first on whether the video stream is contained in a container, so you would have to demultiplex that container first to get the raw video stream. And raw HEVC video streams would have to be parsed sequentially, from the beginning to the end, byte by byte, if you do not already know some smarter approach (e.g. using GOP index chunks in containers which do have some, like ISO Media, e.g. MP4).

[KarthikTdk]

Thanks for your answers
I have another doubt regarding
Intra mode decision
What is the formula used, and anyone know about mode gradient value calculation.

Thank you in advance.