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README.md

libimxvpuapi - frontend for i.MX hardware video codecs

This library provides an API for using hardware video codecs on i.MX platforms. The API abstracts away platform specific details and allows for using the same code with different hardware video codecs on different i.MX platforms.

The hardware video codec is referred to as the VPU.

Currently, the following platforms are supported (listed with their VPUs):

  • i.MX6 (Chips&Media CODA960 codec)
  • i.MX8m (Hantro G1/G2 decoder, no encoder)
  • i.MX8mm (Hantro G1/G2 decoder, Hantro H1 encoder)

Not yet supported:

  • i.MX8 / i.MX8X (Amphion Malone codec)

This is the second version of this library. Differences to the older version are described below.

License

This library is licensed under the LGPL v2.1.

Dependencies

libimxvpuapi depends on libimxdmabuffer.

Additional dependencies are specific to the target platform:

  • i.MX6: imx-vpu package version 3.10.17 or newer.
  • i.MX8m & i.MX8mm: imx-vpu-hantro 1.8.0 or newer. Please note that the build scripts assume that this is a version of the imx-vpu-hantro package with fixed header installation destination. Earlier versions installed all Hantro headers in the main include directory. Newer ones create hantro_enc and hantro_decsubdirectories. libimxvpuapi expects these directories to exist.

Building and installing

This project uses the waf meta build system. To configure , first set the following environment variables to whatever is necessary for cross compilation for your platform:

  • CC
  • CFLAGS
  • LDFLAGS
  • PKG_CONFIG_PATH
  • PKG_CONFIG_SYSROOT_DIR

Then, run:

./waf configure --prefix=PREFIX --imx-platform=IMX_PLATFORM --sysroot-path=SYSROOT

(The aforementioned environment variables are only necessary for this configure call.)

The arguments are as follows:

  • PREFIX defines the installation prefix, that is, where the built binaries will be installed.
  • IMX_PLATFORM specifies what i.MX platform to build for. Valid values currently are imx6, imx8m, imx8mm.
  • SYSROOT is the absolute path to the sysroot for the platform. This is the path where usr/include/imx/mxcfb.h can be found. In cross compilation environments like Yocto or buildroot, this is where the sysroot files for the target i.MX platforms are.

Once configuration is complete, run:

./waf

This builds the library. Finally, to install, run:

./waf install

This will install the headers in $PREFIX/include/imxvpuapi2/, the libraries in $PREFIX/lib/, and generate a pkg-config .pc file, which is placed in $PREFIX/lib/pkgconfig/ .

API documentation

The API is documented in the imxvpuapi/imxvpuapi.h header.

Examples

libimxvpuapi comes with these examples in the example/ directory:

  • decode-example.c : demonstrates how to use the decoder API
  • encode-example.c : demonstrates how to use the encoder API

(Other source files in the example/ directory are common utility code used by all examples above.)

Raw frames are read/written as YUV4MPEG2 (y4m) data, and encoded to / decoded from h.264.

Known issues

i.MX6 VPU timeout

If errors like imx_vpu_api_dec_decode() failed: timeout or VPU blocking: timeout are observed, check if the following workarounds for known problems help:

  • Overclocked VPU: The VPU is clocked at 266 MHz by default (according to the VPU documentation). Some configurations clock the VPU at 352 MHz, and can exhibit VPU timeout problems, particularly during h.264 encoding. Try running the VPU at 266 MHz.

  • Known issue with IPU configuration: As shown by this Github entry, the CONFIG_IMX_IPUV3_CORE kernel config flag can cause problems with the VPU. Disable it, then try again.

  • Low-level VPU library bug: imx-vpu versions prior to 5.4.31 also have been observed to cause VPU timeouts. These seem to be related to the 5.4.31 fix described as: "Fix VPU blocked in BWB module".

VP6 frames decoded upside down by Hantro G1 decoder

This seems to be a bug in imx-vpu-hantro. A workaround is currently not known.

Differences to the older libimxvpuapi version

This is version 2 of libimxvpuapi. Major changes are:

  • The API has been rewritten, and is incompatible with the older one.
  • The imx_vpu_ prefix has been changed to imx_vpu_api_.
  • Files have been renamed from imxvpuapi* to imxvpuapi2 to reflect the new and incompatible API and to allow for coexistence with the old version of the library.
  • DMA allocation functions have been factored out as a separate library, libimxdmabuffer.
  • The old API required checks with imx_vpu_dec_check_if_can_decode() to see if decoding is possible now to avoid a deadlock. This is no longer needed. Decoders either perform internal DMA-based copies of frames (i.MX6, in the same step as detiling from the VPU layout), or accept additional framebuffers in their framebuffer pools on the fly. This simplifies the use of the decoding API considerably.
  • API for getting global en/decoder information and list of supported formats, profiles, levels has been added.
  • Color formats have been merged with the semi/fully planar attribute.
  • h.265 colorimetry information has been added.
  • Encoder API now returns encoded data in a two-step approach: First, the size of the encoded data is returned. Then the user allocates a buffer with at least that size. Finally, that buffer is passed to the encoder to retrieve the encoded data.
  • the imx_vpu_load() and imx_vpu_unload() functions are gone. (Un)loading the i.MX6 VPU firmware is now done internally.
  • 10-bit support and tiled output support have been added (the latter's tiling layout is platform specific).
  • codec_format was renamed to compression_format to avoid confusion with the notion of hardware video codecs.

To do

  • Add more encoder options (and evaluate which ones to add)
  • More wiki entries describing format support per i.MX platform / codec
  • RealVideo decoding support
  • VP8 golden frame and altref frame support during encoding