安卓Root权限下访问编辑语音通话二进制数据及嵌入传输方法咨询

Alright, let's break down your questions one by one—this is all about advanced Android system tinkering, so we'll dive into the low-level details that matter.

First off, it’s critical to understand Android’s voice call stack is heavily locked down for security and carrier compliance. For non-rooted devices, there’s no official way for a regular app to directly intercept or access raw voice data in transit. The Telephony framework handles all audio routing, encoding, and transmission behind the scenes, and these processes are restricted to system-level components only.

If you’re working with a rooted device (which ties directly into your second question), you have two primary avenues:

• Hardware-level audio capture: You can access raw PCM audio streams from the device’s audio interfaces in /dev/snd/ (e.g., /dev/snd/pcmC0D0c for microphone input). Use tools like arecord (from ALSA utilities) or custom C code to capture audio before it’s encoded for transmission.
• Hook system audio services: Use frameworks like Xposed or Frida to hook methods in AudioFlinger or AudioPolicyService—the core system services that route audio. By hooking these, you can siphon off the audio data being sent to the telephony stack.

Short answer: Yes, it’s possible, but it requires deep familiarity with Android’s audio/telephony stack and real-time signal processing. Here’s a practical breakdown:

Step 1: Gain System Access & Map the Data Flow #

With root, you can run code with root or system UID privileges, which unlocks access to restricted system components. The typical voice call data flow looks like this:
Microphone → Raw PCM Audio → AudioFlinger → Telephony Framework → Audio Encoder (AMR/GSM) → Radio Interface → Network → Receiver’s Radio → Decoder → AudioFlinger → Speaker

Your goal is to intercept and modify data either before encoding (raw PCM) or within the encoded binary frames (e.g., AMR) before transmission.

Step 2: Intercept & Modify the Data #

Option A: Modify Raw PCM (Easier for Embedding Data) #

Raw PCM is uncompressed audio, so you can use audio steganography to embed data without disrupting voice quality:

• Use an LSB (Least Significant Bit) embedding algorithm: Replace the least significant bits of PCM samples with your binary data. These bits contribute almost nothing to audio perceptibility, so the voice will sound normal, but your data can be extracted on the other end.
• Implement this by hooking the AudioFlinger method that passes audio to the telephony stack. In your hook, take the PCM buffer, modify samples to include your data, then pass the modified buffer along.

Option B: Modify Encoded Binary Frames (More Efficient) #

If you want to work with already encoded data (like AMR frames), you’ll need to parse the frame structure:

• AMR frames have a fixed header and payload. Some frame types include unused bits or redundancy you can repurpose to store small amounts of data.
• Hook the telephony framework’s encoding function (e.g., in libamrnb.so), intercept the encoded frame, insert your data into redundant sections, then send the modified frame.

Step 3: Enable the Receiver to Extract Data #

The receiving device needs a matching setup to pull out your embedded data:

• For PCM LSB embedding: The rooted receiver hooks the incoming audio stream before decoding, extracts the LSB bits from PCM samples, and reconstructs your data.
• For modified encoded frames: The receiver hooks the decoding function, parses the modified frame, extracts your data, then passes the original frame data to the decoder for normal playback.

Example Simplified Workflow #

1. On the sender’s rooted device, use Frida to hook android.media.AudioRecord’s read() method (captures microphone input).
2. In the hook, run an LSB steganography function to embed a short message (e.g., "Test message") into the PCM byte array.
3. Pass the modified PCM array back to the system for encoding and transmission.
4. On the receiver’s rooted device, hook android.media.AudioTrack’s write() method (receives decoded PCM).
5. Extract the LSB bits from the received PCM array to reconstruct the message.
6. Pass the original PCM data to the speaker so the voice call plays normally.

Key Considerations #

• Real-Time Performance: All modifications must happen instantaneously—any delay will cause audio glitches or dropped calls. Keep processing logic lightweight.
• Carrier/Hardware Compatibility: Some carriers perform integrity checks on voice frames, so modified frames might be rejected. Audio hardware and telephony implementations also vary across devices, so your code may need model-specific tweaks.
• Audio Quality: Over-embedding data can degrade voice quality. Test with small data payloads first to balance functionality and audio clarity.

内容的提问来源于stack exchange，提问作者jamshid