PyObjC CoreMedia Framework

12.1 · active · verified Mon Apr 13

PyObjC-framework-CoreMedia provides Python wrappers for Apple's CoreMedia framework on macOS. It is part of the larger PyObjC project, which creates a bidirectional bridge between Python and Objective-C. The library is actively maintained with frequent releases, often coinciding with new macOS SDKs and Python versions. It is currently at version 12.1 and requires Python 3.10 or newer.

Warnings

breaking PyObjC 12.0 dropped support for Python 3.9. PyObjC 11.0 dropped support for Python 3.8. Users must update their Python environment to Python 3.10 or later.
Fix: Upgrade Python to 3.10 or newer (current version 12.1 requires >=3.10).
breaking Behavior for methods in the 'init' family changed in PyObjC 11.1 to correctly model that they steal a reference to `self` and return a new reference, aligning with `clang`'s Automatic Reference Counting documentation. This may affect custom initializers written in Python.
Fix: Review custom `init` methods for correct reference handling according to ARC semantics, particularly if porting from older PyObjC versions.
gotcha Several low-level C functions in CoreMedia, such as `CMBlockBufferAccessDataBytes` and `CMBlockBufferGetDataPointer`, are not directly usable from Python. Alternative functions like `CMBlockBufferCopyDataBytes` should be used instead.
Fix: Consult PyObjC's API Notes for CoreMedia to identify unsupported C functions and their Python-compatible alternatives.
gotcha When using `CMBlockBufferCreateWithMemoryBlock`, `CMBlockBufferCreateContiguous`, or `CMBlockBufferAppendMemoryBlock`, the `customBlockSource` argument *must* be `None` from Python. Providing a custom block source is not supported.
Fix: Always pass `None` for `customBlockSource` when calling these specific `CMBlockBuffer` creation/modification functions.
gotcha From PyObjC 12.1, Key-Value Observing (KVO) usage is automatically disabled for subclasses of `NSProxy` defined in Python. This prevents potential `SystemError` issues.
Fix: Be aware that KVO will not function for `NSProxy` subclasses implemented in Python. Adjust design or use alternative observation mechanisms if this behavior is critical.
gotcha In PyObjC 10.3, support for calling `__init__` when a class or its superclass had a user-implemented `__new__` was temporarily removed, causing breaking changes for some projects. Version 10.3.1 reinstated this functionality.
Fix: Ensure you are using PyObjC 10.3.1 or later if your code relies on `__init__` being called after a custom `__new__` implementation.

Install

pip install pyobjc-framework-coremedia Install stable version

Imports

CoreMedia
```
import CoreMedia
```
The CoreMedia framework bindings are accessed directly via the 'CoreMedia' package name.
CMTime
```
from CoreMedia import CMTime
```

Quickstart

This example demonstrates importing the CoreMedia framework and creating a basic CMTime object, which is a fundamental structure for representing time in CoreMedia. It then prints some of its properties and converts it to seconds.

import CoreMedia

# Create a CMTime object representing 10 seconds at a 600 timescale
# CMTimeMake(value, timescale) -> CMTime
time_value = CoreMedia.CMTimeMake(10 * 600, 600)

print(f"CMTime object: {time_value}")
print(f"Value: {time_value.value}")
print(f"Timescale: {time_value.timescale}")
print(f"Seconds: {CoreMedia.CMTimeGetSeconds(time_value)}")

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