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HM

HM is the original H.265 reference encoder, predating alternatives like x265. In the modern day, it joins other MPEG reference encoders such as JM & VTM in their reputations for being highly niche offerings that are used rarely due to their usage complexity & speed disadvantages. x264 is more efficient than JM.

HM is capable of producing higher quality streams than highly tuned x265, even at excruciatingly slow speeds. This is only a theoretical advantage, though, as HM is incapable of placing keyframes automatically with scene detection & would need a chunking too reminiscent of Av1an to do this. For videos containing few enough frames where keyframe placement isn’t a concern, HM is better in practice than x265 at the expense of a massive dropoff in speed. HM doesn’t have any threading capabilities & is much slower than even x265 placebo.

Installation

These build instructions are valid for Linux & macOS.

Terminal window
git clone https://vcgit.hhi.fraunhofer.de/jvet/HM
cd HM/
mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
make -j$(nproc)

The binary TAppEncoderStatic or TAppEncoder can be found within the cloned directories, & can be copied to /usr/local/bin for encoding. Decoding & other functions of the reference codec implementation aren’t covered in this entry.

Usage

Here is a sample command: TAppEncoderStatic -i input.yuv -b out.265 -c ~/HM/cfg/encoder_randomaccess_main10.cfg -wdt 1280 -hgt 720 -fr 50 -f 500 -q 27 -xPS 0

Make sure only to use only YUV input when encoding with HM. Each parameter does the following:

  • -i input.yuv -b out.265

Specifies a raw YUV input file & an output raw h265 bitstream. To mux into an MP4 container, it is recommended that you use mp4box instead of muxing with FFmpeg.

  • -c [path/to/config]

Specifies the desired path to your HM configuration file. This makes it easier to encode without having to manually specify a plethora of settings.

  • -wdt 1280 -hgt 720

Sets the input & output width & height.

  • -fr 50 -f 500

Sets the framerate (FPS) & the number of frames to encode. In this case, we are encoding 500 frames of a video that is to be played back at 50fps.

  • -q 27

Sets a quality target for the encoder.

  • -xPS 0

Zero clue what this does. If someone has an idea, please contribute!