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Audio Processing Reference

Comprehensive guide for audio analysis and speech generation using Gemini API.

Audio Understanding

Supported Formats

Format	MIME Type	Best Use
WAV	`audio/wav`	Uncompressed, highest quality
MP3	`audio/mp3`	Compressed, widely compatible
AAC	`audio/aac`	Compressed, good quality
FLAC	`audio/flac`	Lossless compression
OGG Vorbis	`audio/ogg`	Open format
AIFF	`audio/aiff`	Apple format

Specifications

Maximum length: 9.5 hours per request
Multiple files: Unlimited count, combined max 9.5 hours
Token rate: 32 tokens/second (1 minute = 1,920 tokens)
Processing: Auto-downsampled to 16 Kbps mono
File size limits:
- Inline: 20 MB max total request
- File API: 2 GB per file, 20 GB project quota
- Retention: 48 hours auto-delete
Important: if you are going to generate a transcript of the audio, and the audio length is longer than 15 minutes, the transcript often gets truncated due to output token limits in the Gemini API response. To get the full transcript, you need to split the audio into smaller chunks (max 15 minutes per chunk) and transcribe each segment for a complete transcript.

Transcription

Basic Transcription

from google import genai
import os

client = genai.Client(api_key=os.getenv('GEMINI_API_KEY'))

# Upload audio
myfile = client.files.upload(file='meeting.mp3')

# Transcribe
response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Generate a transcript of the speech.', myfile]
)
print(response.text)

With Timestamps

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Generate transcript with timestamps in MM:SS format.', myfile]
)

Multi-Speaker Identification

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Transcribe with speaker labels. Format: [Speaker 1], [Speaker 2], etc.', myfile]
)

Segment-Specific Transcription

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Transcribe only the segment from 02:30 to 05:15.', myfile]
)

Audio Analysis

Summarization

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Summarize key points in 5 bullets with timestamps.', myfile]
)

Non-Speech Audio Analysis

# Music analysis
response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Identify the musical instruments and genre.', myfile]
)

# Environmental sounds
response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Identify all sounds: voices, music, ambient noise.', myfile]
)

# Birdsong identification
response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Identify bird species based on their calls.', myfile]
)

Timestamp-Based Analysis

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['What is discussed from 10:30 to 15:45? Provide key points.', myfile]
)

Input Methods

File Upload (>20MB or Reuse)

# Upload once, use multiple times
myfile = client.files.upload(file='large-audio.mp3')

# First query
response1 = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Transcribe this', myfile]
)

# Second query (reuses same file)
response2 = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Summarize this', myfile]
)

Inline Data (<20MB)

from google.genai import types

with open('small-audio.mp3', 'rb') as f:
    audio_bytes = f.read()

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=[
        'Describe this audio',
        types.Part.from_bytes(data=audio_bytes, mime_type='audio/mp3')
    ]
)

Speech Generation (TTS)

Available Models

Model	Quality	Speed	Cost/1M tokens
`gemini-2.5-flash-native-audio-preview-09-2025`	High	Fast	$10
`gemini-2.5-pro` TTS mode	Premium	Slower	$20

Basic TTS

response = client.models.generate_content(
    model='gemini-2.5-flash-native-audio-preview-09-2025',
    contents='Generate audio: Welcome to today\'s episode.'
)

# Save audio
with open('output.wav', 'wb') as f:
    f.write(response.audio_data)

Controllable Voice Style

# Professional tone
response = client.models.generate_content(
    model='gemini-2.5-flash-native-audio-preview-09-2025',
    contents='Generate audio in a professional, clear tone: Welcome to our quarterly earnings call.'
)

# Casual and friendly
response = client.models.generate_content(
    model='gemini-2.5-flash-native-audio-preview-09-2025',
    contents='Generate audio in a friendly, conversational tone: Hey there! Let\'s dive into today\'s topic.'
)

# Narrative style
response = client.models.generate_content(
    model='gemini-2.5-flash-native-audio-preview-09-2025',
    contents='Generate audio in a narrative, storytelling tone: Once upon a time, in a land far away...'
)

Voice Control Parameters

Style: Professional, casual, narrative, conversational
Pace: Slow, normal, fast
Tone: Friendly, serious, enthusiastic
Accent: Natural language control (e.g., "British accent", "Southern drawl")

Best Practices

File Management

Use File API for files >20MB
Use File API for repeated queries (saves tokens)
Files auto-delete after 48 hours
Clean up manually when done:
```
client.files.delete(name=myfile.name)
```

Prompt Engineering

Effective prompts:

"Transcribe from 02:30 to 03:29 in MM:SS format"
"Identify speakers and extract dialogue with timestamps"
"Summarize key points with relevant timestamps"
"Transcribe and analyze sentiment for each speaker"

Context improves accuracy:

"This is a medical interview - use appropriate terminology"
"Transcribe this legal deposition with precise terminology"
"This is a technical podcast about machine learning"

Combined tasks:

"Transcribe and summarize in bullet points"
"Extract key quotes with timestamps and speaker labels"
"Transcribe and identify action items with timestamps"

Cost Optimization

Token calculation:

1 minute audio = 1,920 tokens
1 hour audio = 115,200 tokens
9.5 hours = 1,094,400 tokens

Model selection:

Use gemini-2.5-flash ($1/1M tokens) for most tasks
Upgrade to gemini-2.5-pro ($3/1M tokens) for complex analysis
For high-volume: gemini-1.5-flash ($0.70/1M tokens)

Reduce costs:

Process only relevant segments using timestamps
Use lower-quality audio when possible
Batch multiple short files in one request
Cache context for repeated queries

Error Handling

import time

def transcribe_with_retry(file_path, max_retries=3):
    """Transcribe audio with exponential backoff retry"""
    for attempt in range(max_retries):
        try:
            myfile = client.files.upload(file=file_path)
            response = client.models.generate_content(
                model='gemini-2.5-flash',
                contents=['Transcribe with timestamps', myfile]
            )
            return response.text
        except Exception as e:
            if attempt == max_retries - 1:
                raise
            wait_time = 2 ** attempt
            print(f"Retry {attempt + 1} after {wait_time}s")
            time.sleep(wait_time)

Common Use Cases

1. Meeting Transcription

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=[
        '''Transcribe this meeting with:
        1. Speaker labels
        2. Timestamps for topic changes
        3. Action items highlighted
        ''',
        myfile
    ]
)

2. Podcast Summary

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=[
        '''Create podcast summary with:
        1. Main topics with timestamps
        2. Key quotes from each speaker
        3. Recommended episode highlights
        ''',
        myfile
    ]
)

3. Interview Analysis

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=[
        '''Analyze interview:
        1. Questions asked with timestamps
        2. Key responses from interviewee
        3. Overall sentiment and tone
        ''',
        myfile
    ]
)

4. Content Verification

response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=[
        '''Verify audio content:
        1. Check for specific keywords or phrases
        2. Identify any compliance issues
        3. Note any concerning statements with timestamps
        ''',
        myfile
    ]
)

5. Multilingual Transcription

# Gemini auto-detects language
response = client.models.generate_content(
    model='gemini-2.5-flash',
    contents=['Transcribe this audio and translate to English if needed.', myfile]
)

Token Costs

Audio Input (32 tokens/second):

1 minute = 1,920 tokens
10 minutes = 19,200 tokens
1 hour = 115,200 tokens
9.5 hours = 1,094,400 tokens

Example costs (Gemini 2.5 Flash at $1/1M):

1 hour audio: 115,200 tokens = $0.12
Full day podcast (8 hours): 921,600 tokens = $0.92

Limitations

Maximum 9.5 hours per request
Auto-downsampled to 16 Kbps mono (quality loss)
Files expire after 48 hours
No real-time streaming support
Non-speech audio less accurate than speech

Current: Audio Processing

Related Capabilities:

Video Analysis - Extract audio from videos
Video Generation - Generate videos with native audio
Image Understanding - Analyze audio with visual context

Back to: AI Multimodal Skill

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