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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 quad (Hantro G1/G2 decoder, no encoder) it is also sometimes referred to as just "the i.MX8m"
  • i.MX8m mini (Hantro G1/G2 decoder, Hantro H1 encoder)
  • i.MX8m plus (Hantro G1/G2 decoder, Hantro VC8000E 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.


This library is licensed under the LGPL v2.1.


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 quad & i.MX8m mini: 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.
  • i.MX8m plus: imx-vpu-hantro 1.8.0 or newer, just like above (since the plus has the same G1 / G2 decoder as the i.MX8m mini), and also imx-vpu-hantro-vc 1.1.0 or newer (for the VC8000E encoder).

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

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. See the list below for the valid values.
  • 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.

Valid IMX_PLATFORM values are:

  • imx6 : i.MX6 (all variants)
  • imx8m : i.MX8m quad
  • imx8mm : i.MX8m mini
  • imx8mp : i.MX8m plus

Once configuration is complete, run:


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.


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 i.MX6 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 i.MX6 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.

imx_vpu_api_dec_add_framebuffers_to_pool() fails on Hantro VPUs, logs show "CODEC_ERROR_UNSPECIFIED" This can happen when too many framebuffers are added. One common situation is when libimxvpuapi is used through gstreamer-imx, and downstream has a queue that soaks up too many buffers. Example:

gst-launch-1.0 filesrc location=test-vp8.mkv ! matroskademux ! imxvpudec_vp8 ! queue ! autovideosink

If the video sink takes a while to start, it is possible that the queue in this example keeps storing more and more buffers without releasing them. This causes the VPU to repeatedly request more framebuffers to decode more frames into. Newer versions of imx-vpu-hantro define upper limits to how many framebuffers can be added, and if these limits are exceeded, the error occurs.

It is recommended to not hold on to too many framebuffers at once. Keep it below 16 framebuffers. In the GStreamer case above, it is sufficient to set the max-size-buffers property of the queue there to 1, since a queue that is right before a video sink is meant for decoupling the upstream portion of that pipeline from the video sink. This helps with reducing the likelihood of lost frames. More than 1 buffer in the queue is not needed for this.

DWL and EWL errors

On machines with Hantro based VPUs, "DWL" and "EWL" errors may appear. DWL and EWL are low level layers used by the Hantro drivers. Errors typically happen when certain device nodes are not available. If such errors occur, check for the presence of:

  • /dev/ion : Used with older imx kernels (<5.15)
  • /dev/dma_heap/linux,cma-uncached : Used with newer imx kernels (>=5.15)
  • /dev/mxc_hantro : Hantro G1 and G2 decoder ; found on the i.MX8m mini, i.MX8m quad, i.MX8m plus
  • /dev/mxc_hantro_h1 : Hantro H1 encoder ; found on the i.MX8m mini
  • /dev/mxc_hantro_vc8000e : Hantro VC8000E encoder ; found on the i.MX8m plus

If at least one of these are missing, check the kernel configuration. The ION and/or the dma-heap CMA allocator needs to be enabled. Also check that the Hantro VPU is enabled.

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