OpenCL Tone Mapping
OpenCL tone mapping runs a software-defined tone-mapping operation through the OpenCL parallel-computing interface.
An OpenCL filter is selected, but processing fails before a picture is delivered. Locating that failure requires three distinct pieces: the application's filter, the runtime's selected device, and the frame representation passed between stages.
| Piece | Responsibility |
|---|---|
| Application/filter | Supplies the mapping program and accepted formats |
| OpenCL platform/runtime | Discovers devices and compiles or loads programs |
| Device/context/queue | Executes the work and provides accessible frame resources |
OpenCL can target supported CPUs or GPUs. The interface name alone does not identify which device was selected or which curve the application implements.
Device contexts, kernels, and frame access
The application chooses a platform and device, creates the relevant context, and obtains a command queue for submitted work. It supplies a kernel program: a function executed across many work items so regions of a picture can be processed in parallel.
Decoded pictures must be made accessible in the filter's expected hardware-frame arrangement. The filter then supplies its color descriptions, range and mapping parameters, launches the program, and makes the result available to the next stage after the required synchronization.
FFmpeg 8.1's OpenCL tone mapper provides a concrete implementation. It checks supported source transfer and component information, prepares the corresponding color/transfer operations, and uses the selected mapping function in its OpenCL program. Its accepted hardware formats constrain that filter's path rather than defining all OpenCL devices' possible formats.
Resolve two different failure cases
No usable OpenCL device appears. Check the runtime and device access in the application's environment. A hardware video decoder can work while a separate compute runtime is absent. A container also needs the applicable runtime and device resources, not only a device visible to the host.
A device is selected but the frame format cannot reach the filter. Inspect the preceding decoder's frame format, the required mapping or upload, and any supported sharing between APIs. Successful device discovery does not supply the missing representation or interoperability operation.
In Emby logs, those stage failures differ from an inability to decode the source codec. Hardware-acceleration documentation describes the surrounding platform options; the bundled implementation and session specify the actual filter route.
Once the path works, frame transfers and synchronization remain part of its cost. Keeping accessible frames across decoding, filtering, and encoding can avoid unnecessary copies. A faster kernel alone may leave the surrounding traffic or another stage as the limiting operation.