Reduce the diff with the pytrch:main branch

[gouzil]

减少与 Pytorch mian 分支的 diff

• 可以通过 meta-pytorch/torchcodec@main...PFCCLab:paddlecodec:paddle 查看现阶段主分支与 Pytorch main diff
• 可以通过 meta-pytorch/torchcodec@main...gouzil:paddlecodec:feat/reduce_diff 查看当前分支 Pytorch main diff

相关链接

• [Cpp API Compatibility] add flatten and narrow related API PaddlePaddle/Paddle#77544
• [Compat] Update DispatchKey usage to c10::DispatchKey and replace dispatch_key_to_string with c10::toString PaddlePaddle/Paddle#78525
• [common] Add support for std::optional in error messages PaddlePaddle/Paddle#78521
• 【Hackathon 10th Spring No.2】Add schema parser and related functionality for Torch compatibility PaddlePaddle/Paddle#77938
• [Cpp API Compatibility] Support BackendSelect dispatch lookup in torch compat PaddlePaddle/Paddle#78591

[Copilot]

Pull request overview

This PR aims to reduce divergence from the upstream PyTorch torchcodec main branch by aligning several C++ core behaviors and operator registrations.

Changes:

• Implemented previously stubbed/unimplemented paths for audio resampler flush (maybeFlushSwrBuffers) and tensor-backed AVIO output (AVIOToTensorContext::getOutputTensor).
• Adjusted custom op registration blocks (including adding a BackendSelect registration block) and minor include/formatting alignment.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/torchcodec/_core/SingleStreamDecoder.cpp	Implements returning flushed resampled audio samples instead of throwing.
src/torchcodec/_core/custom_ops.cpp	Reorders includes and changes TORCH_LIBRARY_IMPL registrations (adds BackendSelect).
src/torchcodec/_core/AVIOTensorContext.cpp	Implements returning the encoded output tensor slice instead of throwing.

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[Copilot]

swr_convert() can return a negative value on error. Passing that directly as the length to lastSamples.narrow(...) will throw an unrelated/cryptic error (or potentially create an invalid slice). Add an explicit check for actualNumRemainingSamples < 0 and surface a clear failure (e.g., TORCH_CHECK(actualNumRemainingSamples >= 0, ...)) before narrowing; optionally also handle the == 0 case explicitly.

Suggested change

	swrContext_.get(), outputBuffers.data(), numRemainingSamples, nullptr, 0);
	swrContext_.get(), outputBuffers.data(), numRemainingSamples, nullptr, 0);
	TORCH_CHECK(
	actualNumRemainingSamples >= 0,
	"swr_convert() failed while flushing buffered audio samples: ",
	actualNumRemainingSamples);
	if (actualNumRemainingSamples == 0) {
	return std::nullopt;
	}

[Copilot]

Registering create_from_tensor under BackendSelect is risky because it has a Tensor argument and the implementation assumes host-accessible memory (no video_tensor.is_cpu() check; it is passed into AVIOFromTensorContext which reads via data_ptr()/memcpy). With this dispatch key change, CUDA tensors may no longer fail dispatch and could reach this CPU-only code path. Consider registering create_from_tensor under CPU (and only keeping no-Tensor factory ops like create_from_file / _get_json_ffmpeg_library_versions under BackendSelect), or add a strict CPU device check for video_tensor if BackendSelect is intentional.