app.py

import os
import uuid
import tempfile
import logging
import math
from typing import List, Optional

from fastapi import FastAPI, File, UploadFile, Form, HTTPException, BackgroundTasks, Query
from fastapi.responses import FileResponse, JSONResponse
from pydub import AudioSegment
from pydub.exceptions import CouldntDecodeError

# --- Configuration & Setup ---
TEMP_DIR = tempfile.gettempdir()
os.makedirs(TEMP_DIR, exist_ok=True)

# Configure logging
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

# --- FastAPI App Initialization ---
app = FastAPI(
    title="Enhanced Audio Editor API",
    description="API for various audio editing tasks including trim, concat, volume, convert, fade, reverse, normalize, overlay, info, silence, speed. Requires FFmpeg.",
    version="2.0.0",
)

# --- Helper Functions (Slightly Enhanced) ---

def cleanup_file(file_path: str):
    """Safely remove a file."""
    try:
        if os.path.exists(file_path):
            os.remove(file_path)
            logger.info(f"Cleaned up temporary file: {file_path}")
    except Exception as e:
        logger.error(f"Error cleaning up file {file_path}: {e}", exc_info=True)

async def save_upload_file(upload_file: UploadFile) -> str:
    """Saves an uploaded file to a temporary location and returns the path."""
    file_extension = os.path.splitext(upload_file.filename)[1].lower() or '.tmp'
    temp_file_path = os.path.join(TEMP_DIR, f"{uuid.uuid4().hex}{file_extension}")
    try:
        with open(temp_file_path, "wb") as buffer:
            while content := await upload_file.read(1024 * 1024):
                buffer.write(content)
        logger.info(f"Saved uploaded file '{upload_file.filename}' to temp path: {temp_file_path}")
        return temp_file_path
    except Exception as e:
        logger.error(f"Failed to save uploaded file {upload_file.filename}: {e}", exc_info=True)
        cleanup_file(temp_file_path)
        raise HTTPException(status_code=500, detail=f"Could not save uploaded file: {upload_file.filename}")
    finally:
        await upload_file.close()

def load_audio(file_path: str) -> AudioSegment:
    """Loads an audio file using pydub."""
    try:
        audio = AudioSegment.from_file(file_path)
        logger.info(f"Loaded audio from: {file_path} ({len(audio)}ms)")
        return audio
    except CouldntDecodeError:
        logger.warning(f"pydub couldn't decode file: {file_path}. Check format/corruption/FFmpeg.")
        raise HTTPException(status_code=415, detail=f"Unsupported audio format or corrupted file: {os.path.basename(file_path)}. Ensure FFmpeg is correctly installed and supports the format.")
    except FileNotFoundError:
         logger.error(f"Audio file not found after saving: {file_path}")
         raise HTTPException(status_code=500, detail="Internal error: Temporary audio file missing.")
    except Exception as e:
        logger.error(f"Error loading audio file {file_path}: {e}", exc_info=True)
        raise HTTPException(status_code=500, detail=f"Error processing audio file: {os.path.basename(file_path)}")

def export_audio(audio: AudioSegment, format: str, bitrate: Optional[str] = None) -> str:
    """Exports an AudioSegment to a temporary file and returns the path. Supports bitrate."""
    output_filename = f"edited_{uuid.uuid4().hex}.{format}"
    output_path = os.path.join(TEMP_DIR, output_filename)
    export_params = {}
    if bitrate and format in ['mp3', 'ogg', 'aac', 'm4a']: # Add other formats if they support bitrate param in pydub/ffmpeg
        export_params['bitrate'] = bitrate
        logger.info(f"Using bitrate: {bitrate} for export.")

    try:
        logger.info(f"Exporting audio to format '{format}' at {output_path}")
        audio.export(output_path, format=format, **export_params)
        return output_path
    except Exception as e:
        logger.error(f"Error exporting audio to format {format} (bitrate: {bitrate}): {e}", exc_info=True)
        cleanup_file(output_path)
        raise HTTPException(status_code=500, detail=f"Failed to export audio to format '{format}'. Check format support and parameters.")

# --- API Endpoints ---

# --- General ---
@app.get("/", tags=["General"])
def read_root():
    """Root endpoint providing a welcome message."""
    return {"message": "Welcome to the Enhanced Audio Editor API. Use POST requests to the specific editing endpoints."}

@app.post("/info", tags=["General"])
async def get_audio_info(
    background_tasks: BackgroundTasks,
    file: UploadFile = File(..., description="Audio file to analyze.")
):
    """Retrieves basic information about the uploaded audio file."""
    logger.info(f"Info request: file='{file.filename}'")
    input_path = await save_upload_file(file)
    background_tasks.add_task(cleanup_file, input_path) # Schedule cleanup

    try:
        audio = load_audio(input_path)
        info = {
            "filename": file.filename,
            "duration_ms": len(audio),
            "duration_seconds": len(audio) / 1000.0,
            "channels": audio.channels,
            "sample_width_bytes": audio.sample_width,
            "frame_rate_hz": audio.frame_rate,
            "frame_count": audio.frame_count(),
            "max_amplitude": audio.max, # Max sample value (peak)
            "rms_amplitude": audio.rms, # Root Mean Square amplitude (average loudness)
            "dBFS": audio.dBFS,         # Peak amplitude in dBFS
        }
        logger.info(f"Audio info retrieved for '{file.filename}': {info}")
        return JSONResponse(content=info)
    except Exception as e:
        logger.error(f"Error during info operation: {e}", exc_info=True)
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred while getting audio info: {str(e)}")


# --- Basic Editing ---
@app.post("/trim", tags=["Basic Editing"])
async def trim_audio(
    background_tasks: BackgroundTasks,
    file: UploadFile = File(..., description="Audio file to trim."),
    start_ms: int = Form(..., description="Start time in milliseconds."),
    end_ms: int = Form(..., description="End time in milliseconds.")
):
    """Trims an audio file to the specified start and end times (in milliseconds)."""
    if start_ms < 0 or end_ms <= start_ms:
        raise HTTPException(status_code=422, detail="Invalid start/end times. Ensure start_ms >= 0 and end_ms > start_ms.")

    logger.info(f"Trim request: file='{file.filename}', start={start_ms}ms, end={end_ms}ms")
    input_path = await save_upload_file(file)
    background_tasks.add_task(cleanup_file, input_path)

    try:
        audio = load_audio(input_path)
        if end_ms > len(audio):
             logger.warning(f"End time ({end_ms}ms) exceeds audio duration ({len(audio)}ms). Trimming to end.")
             end_ms = len(audio)
        if start_ms >= len(audio):
             raise HTTPException(status_code=422, detail=f"Start time ({start_ms}ms) is beyond audio duration ({len(audio)}ms).")


        trimmed_audio = audio[start_ms:end_ms]
        logger.info(f"Audio trimmed to {len(trimmed_audio)}ms")

        original_format = os.path.splitext(file.filename)[1][1:].lower() or "mp3"
        if not original_format or original_format == "tmp": original_format = "mp3"

        output_path = export_audio(trimmed_audio, original_format)
        background_tasks.add_task(cleanup_file, output_path)

        return FileResponse(
            path=output_path,
            media_type=f"audio/{original_format}",
            filename=f"trimmed_{start_ms}-{end_ms}ms_{file.filename}"
        )
    except Exception as e:
        logger.error(f"Error during trim operation: {e}", exc_info=True)
        if 'output_path' in locals() and os.path.exists(output_path): cleanup_file(output_path)
        # Input cleanup is handled by background task unless saving failed earlier
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred during trimming: {str(e)}")

@app.post("/concat", tags=["Basic Editing"])
async def concatenate_audio(
    background_tasks: BackgroundTasks,
    files: List[UploadFile] = File(..., description="Two or more audio files to join in order."),
    output_format: str = Form("mp3", description="Desired output format (e.g., 'mp3', 'wav', 'ogg')."),
    crossfade_ms: int = Form(0, description="Duration of crossfade between segments in milliseconds (0 for no crossfade).")
):
    """Concatenates two or more audio files sequentially, optionally with crossfade."""
    if len(files) < 2:
        raise HTTPException(status_code=422, detail="Please upload at least two files to concatenate.")
    if crossfade_ms < 0:
        raise HTTPException(status_code=422, detail="Crossfade duration cannot be negative.")

    logger.info(f"Concatenate request: {len(files)} files, format='{output_format}', crossfade={crossfade_ms}ms")
    input_paths = []
    loaded_audios = []
    output_path = None # Define to allow cleanup in finally

    try:
        for file in files:
            input_path = await save_upload_file(file)
            input_paths.append(input_path)
            background_tasks.add_task(cleanup_file, input_path)
            audio = load_audio(input_path)
            loaded_audios.append(audio)

        if not loaded_audios:
             raise HTTPException(status_code=500, detail="No audio segments were loaded successfully.")

        combined_audio = loaded_audios[0]
        logger.info(f"Starting concatenation with first segment ({len(combined_audio)}ms)")
        for i in range(1, len(loaded_audios)):
            logger.info(f"Adding segment {i+1} ({len(loaded_audios[i])}ms)")
            # Use crossfade parameter if provided
            combined_audio = combined_audio.append(loaded_audios[i], crossfade=crossfade_ms)

        logger.info(f"Concatenated audio length: {len(combined_audio)}ms")

        output_path = export_audio(combined_audio, output_format)
        background_tasks.add_task(cleanup_file, output_path)

        first_filename_base = os.path.splitext(files[0].filename)[0]
        output_filename = f"concat_{first_filename_base}_and_{len(files)-1}_others.{output_format}"

        return FileResponse(path=output_path, media_type=f"audio/{output_format}", filename=output_filename)
    except Exception as e:
        logger.error(f"Error during concat operation: {e}", exc_info=True)
        # Cleanup output if it exists and error happened after export
        if output_path and os.path.exists(output_path): cleanup_file(output_path)
        # Input cleanup is handled by background tasks
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred during concatenation: {str(e)}")

@app.post("/volume", tags=["Basic Editing"])
async def change_volume(
    background_tasks: BackgroundTasks,
    file: UploadFile = File(..., description="Audio file to adjust volume for."),
    change_db: float = Form(..., description="Volume change in decibels (dB). Positive increases, negative decreases.")
):
    """Adjusts the volume of an audio file by a specified decibel amount."""
    logger.info(f"Volume request: file='{file.filename}', change_db={change_db}dB")
    input_path = await save_upload_file(file)
    background_tasks.add_task(cleanup_file, input_path)
    output_path = None

    try:
        audio = load_audio(input_path)
        adjusted_audio = audio + change_db
        logger.info(f"Volume adjusted by {change_db}dB.")

        original_format = os.path.splitext(file.filename)[1][1:].lower() or "mp3"
        if not original_format or original_format == "tmp": original_format = "mp3"

        output_path = export_audio(adjusted_audio, original_format)
        background_tasks.add_task(cleanup_file, output_path)

        return FileResponse(path=output_path, media_type=f"audio/{original_format}", filename=f"volume_{change_db}dB_{file.filename}")
    except Exception as e:
        logger.error(f"Error during volume operation: {e}", exc_info=True)
        if output_path and os.path.exists(output_path): cleanup_file(output_path)
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred during volume adjustment: {str(e)}")

@app.post("/convert", tags=["Basic Editing"])
async def convert_format(
    background_tasks: BackgroundTasks,
    file: UploadFile = File(..., description="Audio file to convert."),
    output_format: str = Form(..., description="Target audio format (e.g., 'mp3', 'wav', 'ogg', 'flac', 'aac')."),
    bitrate: Optional[str] = Form(None, description="Target bitrate (e.g., '192k', '320k'). Only applicable for certain formats like MP3, OGG, AAC.")
):
    """Converts an audio file to a different format, optionally specifying bitrate."""
    allowed_formats = {'mp3', 'wav', 'ogg', 'flac', 'aac', 'm4a', 'opus'} # Common formats
    output_format = output_format.lower()
    if output_format not in allowed_formats:
         raise HTTPException(status_code=422, detail=f"Invalid output format '{output_format}'. Allowed: {', '.join(allowed_formats)}")

    logger.info(f"Convert request: file='{file.filename}', format='{output_format}', bitrate='{bitrate}'")
    input_path = await save_upload_file(file)
    background_tasks.add_task(cleanup_file, input_path)
    output_path = None

    try:
        audio = load_audio(input_path)
        output_path = export_audio(audio, output_format, bitrate=bitrate)
        background_tasks.add_task(cleanup_file, output_path)

        filename_base = os.path.splitext(file.filename)[0]
        output_filename = f"{filename_base}_converted.{output_format}"

        return FileResponse(path=output_path, media_type=f"audio/{output_format}", filename=output_filename)
    except Exception as e:
        logger.error(f"Error during convert operation: {e}", exc_info=True)
        if output_path and os.path.exists(output_path): cleanup_file(output_path)
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred during format conversion: {str(e)}")

# --- Effects & Advanced Editing ---
@app.post("/fade", tags=["Effects & Advanced"])
async def apply_fade(
    background_tasks: BackgroundTasks,
    file: UploadFile = File(..., description="Audio file to apply fade."),
    fade_type: str = Form(..., description="Type of fade: 'in' or 'out'."),
    duration_ms: int = Form(..., description="Duration of the fade in milliseconds.")
):
    """Applies a fade-in or fade-out effect to the audio."""
    if fade_type not in ['in', 'out']:
        raise HTTPException(status_code=422, detail="Invalid fade_type. Must be 'in' or 'out'.")
    if duration_ms <= 0:
        raise HTTPException(status_code=422, detail="Fade duration must be positive.")

    logger.info(f"Fade request: file='{file.filename}', type='{fade_type}', duration={duration_ms}ms")
    input_path = await save_upload_file(file)
    background_tasks.add_task(cleanup_file, input_path)
    output_path = None

    try:
        audio = load_audio(input_path)
        if duration_ms > len(audio):
             logger.warning(f"Fade duration ({duration_ms}ms) exceeds audio length ({len(audio)}ms). Clamping.")
             duration_ms = len(audio)

        if fade_type == 'in':
            faded_audio = audio.fade_in(duration_ms)
        else: # fade_type == 'out'
            faded_audio = audio.fade_out(duration_ms)
        logger.info(f"Fade-{fade_type} applied successfully.")

        original_format = os.path.splitext(file.filename)[1][1:].lower() or "mp3"
        if not original_format or original_format == "tmp": original_format = "mp3"

        output_path = export_audio(faded_audio, original_format)
        background_tasks.add_task(cleanup_file, output_path)

        return FileResponse(path=output_path, media_type=f"audio/{original_format}", filename=f"fade_{fade_type}_{duration_ms}ms_{file.filename}")
    except Exception as e:
        logger.error(f"Error during fade operation: {e}", exc_info=True)
        if output_path and os.path.exists(output_path): cleanup_file(output_path)
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred during fade: {str(e)}")

@app.post("/reverse", tags=["Effects & Advanced"])
async def reverse_audio(
    background_tasks: BackgroundTasks,
    file: UploadFile = File(..., description="Audio file to reverse.")
):
    """Reverses the audio playback."""
    logger.info(f"Reverse request: file='{file.filename}'")
    input_path = await save_upload_file(file)
    background_tasks.add_task(cleanup_file, input_path)
    output_path = None

    try:
        audio = load_audio(input_path)
        reversed_audio = audio.reverse()
        logger.info("Audio reversed successfully.")

        original_format = os.path.splitext(file.filename)[1][1:].lower() or "mp3"
        if not original_format or original_format == "tmp": original_format = "mp3"

        output_path = export_audio(reversed_audio, original_format)
        background_tasks.add_task(cleanup_file, output_path)

        return FileResponse(path=output_path, media_type=f"audio/{original_format}", filename=f"reversed_{file.filename}")
    except Exception as e:
        logger.error(f"Error during reverse operation: {e}", exc_info=True)
        if output_path and os.path.exists(output_path): cleanup_file(output_path)
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred during reverse: {str(e)}")

@app.post("/normalize", tags=["Effects & Advanced"])
async def normalize_audio(
    background_tasks: BackgroundTasks,
    file: UploadFile = File(..., description="Audio file to normalize."),
    headroom_db: float = Form(0.1, description="Target peak amplitude headroom in dB below 0 dBFS. Default is 0.1dB.")
):
    """Normalizes the audio volume so the peak is at -headroom_db dBFS."""
    if headroom_db < 0:
        raise HTTPException(status_code=422, detail="Headroom must be non-negative.")

    logger.info(f"Normalize request: file='{file.filename}', headroom={headroom_db}dB")
    input_path = await save_upload_file(file)
    background_tasks.add_task(cleanup_file, input_path)
    output_path = None

    try:
        audio = load_audio(input_path)
        normalized_audio = audio.normalize(headroom=headroom_db)
        logger.info(f"Audio normalized with {headroom_db}dB headroom.")

        original_format = os.path.splitext(file.filename)[1][1:].lower() or "mp3"
        if not original_format or original_format == "tmp": original_format = "mp3"

        output_path = export_audio(normalized_audio, original_format)
        background_tasks.add_task(cleanup_file, output_path)

        return FileResponse(path=output_path, media_type=f"audio/{original_format}", filename=f"normalized_{headroom_db}dB_{file.filename}")
    except Exception as e:
        logger.error(f"Error during normalize operation: {e}", exc_info=True)
        if output_path and os.path.exists(output_path): cleanup_file(output_path)
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred during normalization: {str(e)}")

@app.post("/overlay", tags=["Effects & Advanced"])
async def overlay_audio(
    background_tasks: BackgroundTasks,
    file_base: UploadFile = File(..., description="The base audio track."),
    file_overlay: UploadFile = File(..., description="The audio track to overlay."),
    position_ms: int = Form(0, description="Position (in ms) in the base track where the overlay should start."),
    # loop: bool = Form(False, description="Whether to loop the overlay track if it's shorter than needed."), # Pydub overlay doesn't directly support count-limited loop, only infinite or no loop
    # times: int = Form(1, description="How many times to loop the overlay (if loop=True). 'inf' for infinite.") # See above note
    gain_during_overlay: Optional[float] = Form(None, description="Volume change (dB) applied to the base track *during* the overlay. E.g., -6 to lower base volume.")
):
    """Overlays (mixes) one audio file onto another at a specific position."""
    if position_ms < 0:
        raise HTTPException(status_code=422, detail="Overlay position cannot be negative.")

    logger.info(f"Overlay request: base='{file_base.filename}', overlay='{file_overlay.filename}', position={position_ms}ms, gain_during={gain_during_overlay}dB")
    input_path_base = None
    input_path_overlay = None
    output_path = None

    try:
        input_path_base = await save_upload_file(file_base)
        background_tasks.add_task(cleanup_file, input_path_base)
        input_path_overlay = await save_upload_file(file_overlay)
        background_tasks.add_task(cleanup_file, input_path_overlay)

        audio_base = load_audio(input_path_base)
        audio_overlay = load_audio(input_path_overlay)

        # Note: pydub's gain_during_overlay is relative to the segment's *current* volume, not absolute dBFS.
        # It applies the gain change only to the portion of the base track that overlaps with the overlay.
        overlaid_audio = audio_base.overlay(
            audio_overlay,
            position=position_ms,
            gain_during_overlay=gain_during_overlay if gain_during_overlay is not None else 0 # pydub needs a numerical value
        )
        logger.info("Overlay applied successfully.")

        original_format = os.path.splitext(file_base.filename)[1][1:].lower() or "mp3"
        if not original_format or original_format == "tmp": original_format = "mp3"

        output_path = export_audio(overlaid_audio, original_format)
        background_tasks.add_task(cleanup_file, output_path)

        base_name = os.path.splitext(file_base.filename)[0]
        overlay_name = os.path.splitext(file_overlay.filename)[0]

        return FileResponse(path=output_path, media_type=f"audio/{original_format}", filename=f"overlay_{base_name}_with_{overlay_name}.{original_format}")
    except Exception as e:
        logger.error(f"Error during overlay operation: {e}", exc_info=True)
        if output_path and os.path.exists(output_path): cleanup_file(output_path)
        # Input cleanups handled by background tasks
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred during overlay: {str(e)}")


@app.post("/add-silence", tags=["Effects & Advanced"])
async def add_silence(
    background_tasks: BackgroundTasks,
    file: UploadFile = File(..., description="Audio file to add silence to."),
    duration_ms: int = Form(..., description="Duration of silence in milliseconds."),
    position: str = Form("end", description="Position to add silence: 'start' or 'end'.")
):
    """Adds a period of silence to the beginning or end of an audio file."""
    if duration_ms <= 0:
         raise HTTPException(status_code=422, detail="Silence duration must be positive.")
    if position not in ['start', 'end']:
         raise HTTPException(status_code=422, detail="Position must be 'start' or 'end'.")

    logger.info(f"Add silence request: file='{file.filename}', duration={duration_ms}ms, position='{position}'")
    input_path = await save_upload_file(file)
    background_tasks.add_task(cleanup_file, input_path)
    output_path = None

    try:
        audio = load_audio(input_path)
        silence = AudioSegment.silent(duration=duration_ms, frame_rate=audio.frame_rate) # Match frame rate

        if position == 'start':
            modified_audio = silence + audio
        else: # position == 'end'
            modified_audio = audio + silence
        logger.info(f"Silence added successfully to {position}.")

        original_format = os.path.splitext(file.filename)[1][1:].lower() or "mp3"
        if not original_format or original_format == "tmp": original_format = "mp3"

        output_path = export_audio(modified_audio, original_format)
        background_tasks.add_task(cleanup_file, output_path)

        return FileResponse(path=output_path, media_type=f"audio/{original_format}", filename=f"silence_{position}_{duration_ms}ms_{file.filename}")
    except Exception as e:
        logger.error(f"Error during add silence operation: {e}", exc_info=True)
        if output_path and os.path.exists(output_path): cleanup_file(output_path)
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred while adding silence: {str(e)}")

@app.post("/speedup", tags=["Effects & Advanced"])
async def change_speed(
    background_tasks: BackgroundTasks,
    file: UploadFile = File(..., description="Audio file to change speed of."),
    playback_speed: float = Form(..., gt=0, description="Playback speed multiplier (e.g., 1.5 for 50% faster, 0.8 for 20% slower). Note: Affects pitch.")
):
    """Changes the playback speed of the audio. WARNING: This basic method also changes the pitch."""
    if playback_speed <= 0:
         raise HTTPException(status_code=422, detail="Playback speed must be positive.")

    logger.info(f"Speed change request: file='{file.filename}', speed={playback_speed}x")
    input_path = await save_upload_file(file)
    background_tasks.add_task(cleanup_file, input_path)
    output_path = None

    try:
        audio = load_audio(input_path)
        # Pydub's speedup changes pitch. More complex methods exist for time-stretching without pitch shift (e.g., using rubberband via ffmpeg), but not directly in pydub.
        # We need to manipulate the frame rate directly for speed changes *with* pitch shift
        new_frame_rate = int(audio.frame_rate * playback_speed)
        logger.info(f"Original frame rate: {audio.frame_rate}, New frame rate: {new_frame_rate}")
        speed_changed_audio = audio._spawn(audio.raw_data, overrides={'frame_rate': new_frame_rate})

        # Recalculate duration based on speed change
        new_duration = len(audio) / playback_speed
        logger.info(f"Speed changed by {playback_speed}x. New duration approx {new_duration:.2f}ms (pitch also changed).")


        original_format = os.path.splitext(file.filename)[1][1:].lower() or "mp3"
        if not original_format or original_format == "tmp": original_format = "mp3"

        # Set frame rate back to original for export compatibility? Or keep changed rate?
        # Keeping the changed rate reflects the speed change. Some players might handle it; others might play at the wrong speed/pitch if they ignore the rate.
        # Let's try keeping the modified rate first.
        output_path = export_audio(speed_changed_audio.set_frame_rate(new_frame_rate), original_format)
        background_tasks.add_task(cleanup_file, output_path)

        return FileResponse(path=output_path, media_type=f"audio/{original_format}", filename=f"speed_{playback_speed}x_{file.filename}")
    except Exception as e:
        logger.error(f"Error during speed change operation: {e}", exc_info=True)
        if output_path and os.path.exists(output_path): cleanup_file(output_path)
        if isinstance(e, HTTPException): raise e
        else: raise HTTPException(status_code=500, detail=f"An unexpected error occurred during speed change: {str(e)}")


# --- How to Run ---
# 1. Ensure FFmpeg is installed and in PATH.
# 2. Save as `app.py`, create/update `requirements.txt`.
# 3. `pip install -r requirements.txt`
# 4. `uvicorn app:app --reload`
#
# --- Example Usage (New Endpoints with curl) ---
#
# **Fade In:** (Fade in input.wav over 500ms)
# curl -X POST "http://127.0.0.1:8000/fade" \
#      -F "[email protected]" \
#      -F "fade_type=in" \
#      -F "duration_ms=500" \
#      --output faded_in_output.wav
#
# **Reverse:** (Reverse input.mp3)
# curl -X POST "http://127.0.0.1:8000/reverse" \
#      -F "[email protected]" \
#      --output reversed_output.mp3
#
# **Normalize:** (Normalize input.ogg to peak at -0.5 dBFS)
# curl -X POST "http://127.0.0.1:8000/normalize" \
#      -F "[email protected]" \
#      -F "headroom_db=0.5" \
#      --output normalized_output.ogg
#
# **Overlay:** (Overlay effect.wav onto base.mp3 starting at 2000ms)
# curl -X POST "http://127.0.0.1:8000/overlay" \
#      -F "[email protected]" \
#      -F "[email protected]" \
#      -F "position_ms=2000" \
#      --output overlay_output.mp3
#
# **Get Info:** (Get info about input.flac - returns JSON, not a file)
# curl -X POST "http://127.0.0.1:8000/info" \
#      -F "[email protected]"
#
# **Add Silence:** (Add 1500ms silence to the start of input.m4a)
# curl -X POST "http://127.0.0.1:8000/add-silence" \
#      -F "[email protected]" \
#      -F "duration_ms=1500" \
#      -F "position=start" \
#      --output silence_start_output.m4a
#
# **Change Speed:** (Make input.wav play 50% faster - pitch will increase)
# curl -X POST "http://127.0.0.1:8000/speedup" \
#      -F "[email protected]" \
#      -F "playback_speed=1.5" \
#      --output speed_1.5x_output.wav
#
# **Convert with Bitrate:** (Convert input.wav to MP3 at 192kbps)
# curl -X POST "http://127.0.0.1:8000/convert" \
#      -F "[email protected]" \
#      -F "output_format=mp3" \
#      -F "bitrate=192k" \
#      --output converted_192k_output.mp3
#