Add export_utils file for exporting LTX 2.0 videos with audio

src/diffusers/pipelines/ltx2/export_utils.py

@@ -0,0 +1,134 @@
+# Copyright 2025 The Lightricks team and The HuggingFace Team.
+# All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from fractions import Fraction
+from typing import Optional
+
+import torch
+
+from ...utils import is_av_available
+
+
+_CAN_USE_AV = is_av_available()
+if _CAN_USE_AV:
+    import av
+else:
+    raise ImportError(
+        "PyAV is required to use LTX 2.0 video export utilities. You can install it with `pip install av`"
+    )
+
+
+def _prepare_audio_stream(container: av.container.Container, audio_sample_rate: int) -> av.audio.AudioStream:
+    """
+    Prepare the audio stream for writing.
+    """
+    audio_stream = container.add_stream("aac", rate=audio_sample_rate)
+    audio_stream.codec_context.sample_rate = audio_sample_rate
+    audio_stream.codec_context.layout = "stereo"
+    audio_stream.codec_context.time_base = Fraction(1, audio_sample_rate)
+    return audio_stream
+
+
+def _resample_audio(
+    container: av.container.Container, audio_stream: av.audio.AudioStream, frame_in: av.AudioFrame
+) -> None:
+    cc = audio_stream.codec_context
+
+    # Use the encoder's format/layout/rate as the *target*
+    target_format = cc.format or "fltp"  # AAC → usually fltp
+    target_layout = cc.layout or "stereo"
+    target_rate = cc.sample_rate or frame_in.sample_rate
+
+    audio_resampler = av.audio.resampler.AudioResampler(
+        format=target_format,
+        layout=target_layout,
+        rate=target_rate,
+    )
+
+    audio_next_pts = 0
+    for rframe in audio_resampler.resample(frame_in):
+        if rframe.pts is None:
+            rframe.pts = audio_next_pts
+        audio_next_pts += rframe.samples
+        rframe.sample_rate = frame_in.sample_rate
+        container.mux(audio_stream.encode(rframe))
+
+    # flush audio encoder
+    for packet in audio_stream.encode():
+        container.mux(packet)
+
+
+def _write_audio(
+    container: av.container.Container,
+    audio_stream: av.audio.AudioStream,
+    samples: torch.Tensor,
+    audio_sample_rate: int,
+) -> None:
+    if samples.ndim == 1:
+        samples = samples[:, None]
+
+    if samples.shape[1] != 2 and samples.shape[0] == 2:
+        samples = samples.T
+
+    if samples.shape[1] != 2:
+        raise ValueError(f"Expected samples with 2 channels; got shape {samples.shape}.")
+
+    # Convert to int16 packed for ingestion; resampler converts to encoder fmt.
+    if samples.dtype != torch.int16:
+        samples = torch.clip(samples, -1.0, 1.0)
+        samples = (samples * 32767.0).to(torch.int16)
+
+    frame_in = av.AudioFrame.from_ndarray(
+        samples.contiguous().reshape(1, -1).cpu().numpy(),
+        format="s16",
+        layout="stereo",
+    )
+    frame_in.sample_rate = audio_sample_rate
+
+    _resample_audio(container, audio_stream, frame_in)
+
+
+def encode_video(
+    video: torch.Tensor, fps: int, audio: Optional[torch.Tensor], audio_sample_rate: Optional[int], output_path: str
+) -> None:
+    video_np = video.cpu().numpy()
+
+    _, height, width, _ = video_np.shape
+
+    container = av.open(output_path, mode="w")
+    stream = container.add_stream("libx264", rate=int(fps))
+    stream.width = width
+    stream.height = height
+    stream.pix_fmt = "yuv420p"
+
+    if audio is not None:
+        if audio_sample_rate is None:
+            raise ValueError("audio_sample_rate is required when audio is provided")
+
+        audio_stream = _prepare_audio_stream(container, audio_sample_rate)
+
+    for frame_array in video_np:
+        frame = av.VideoFrame.from_ndarray(frame_array, format="rgb24")
+        for packet in stream.encode(frame):
+            container.mux(packet)
+
+    # Flush encoder
+    for packet in stream.encode():
+        container.mux(packet)
+
+    if audio is not None:
+        _write_audio(container, audio_stream, audio, audio_sample_rate)
+
+    container.close()

src/diffusers/utils/__init__.py

@@ -66,6 +66,7 @@ from .import_utils import (
     is_accelerate_version,
     is_aiter_available,
     is_aiter_version,
+    is_av_available,
     is_better_profanity_available,
     is_bitsandbytes_available,
     is_bitsandbytes_version,

src/diffusers/utils/import_utils.py

@@ -230,6 +230,7 @@ _flash_attn_3_available, _flash_attn_3_version = _is_package_available("flash_at
 _aiter_available, _aiter_version = _is_package_available("aiter")
 _kornia_available, _kornia_version = _is_package_available("kornia")
 _nvidia_modelopt_available, _nvidia_modelopt_version = _is_package_available("modelopt", get_dist_name=True)
+_av_available, _av_version = _is_package_available("av")
 
 
 def is_torch_available():
@@ -420,6 +421,10 @@ def is_kornia_available():
     return _kornia_available
 
 
+def is_av_available():
+    return _av_available
+
+
 # docstyle-ignore
 FLAX_IMPORT_ERROR = """
 {0} requires the FLAX library but it was not found in your environment. Checkout the instructions on the