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How to use av.CodecContext.create(..., hwaccel=...) with raw H265 chunks? #1908
Description
Title: Unable to use av.CodecContext.create(..., hwaccel=...) with raw H265 chunks and videotoolbox on macOS
Hi PyAV team,
I'm trying to build a real-time H265 decoding pipeline using PyAV on macOS, with hardware-accelerated decoding via VideoToolbox.
I noticed that av.CodecContext.create(codec_name, 'r', hwaccel=...) accepts a third hwaccel argument, and I attempted to use it like this.
✅ What I'm Trying to Do
- Decode raw H265 chunks (Annex B NALUs, received from a stream), not a complete
.h265or.mp4file. - Use
videotoolboxas a hardware accelerator for performance. - Convert decoded frames to BGR using
.to_ndarray("bgr24"), and pass to OpenCV for post-processing. - Avoid using
av.open() and demux— my use case works directly with stream fragments.
🧪 My Attempt (Non-working Code)
import av
import cv2
from av.codec import hwaccel
def decode_h265_chunk_videotoolbox(chunk: bytes):
"""
Decode a raw H265 chunk using VideoToolbox hardware acceleration on macOS.
This does NOT require a complete video container, just raw NALUs.
:param chunk: Raw H265 encoded data (e.g. Annex B NALU stream)
:return: List of BGR frames (decoded)
"""
# Create hardware accelerator (macOS only: 'videotoolbox')
accel = hwaccel.HWAccel("videotoolbox")
# Create decoder context with hardware acceleration
codec_ctx = av.CodecContext.create("hevc", "r", hwaccel=accel)
# Decode raw chunk
frames = []
try:
packets = codec_ctx.parse(chunk)
for packet in packets:
decoded = codec_ctx.decode(packet)
for frame in decoded:
img = frame.to_ndarray(format="bgr24")
frames.append(img)
except av.FFmpegError as e:
# Example error:
# Decoding failed: [Errno 1313558101] Unknown error occurred: 'avcodec_send_packet()'
print(f"Decoding failed: {e}")
return frames
# === Test entrypoint ===
if __name__ == "__main__":
# Simulate a raw H265 NALU chunk
with open("./test.h265", "rb") as f:
chunk = f.read()
frames = decode_h265_chunk_videotoolbox(chunk)
for i, frame in enumerate(frames):
cv2.imshow(f"frame-{i}", frame)
cv2.waitKey(0)
cv2.destroyAllWindows()Decoding failed: [Errno 1313558101] Unknown error occurred: 'avcodec_send_packet()'
My Questions
- Does PyAV currently support using videotoolbox with CodecContext.decode() on raw H265 NALU streams (not full containers)?
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