# **FFmpeg: Generating Fixed Binary Digit Filename Patterns**

We frequently encounter scenarios where precise control over video file segments is paramount. While FFmpeg offers versatile tools for capturing and manipulating video streams, achieving a specific filename pattern, such as one based on fixed-width binary digits, demands a more intricate approach. This article delves into the techniques required to generate filenames reflecting binary representations of time increments, offering granular control over video segments and enabling efficient filtering based on binary patterns. We will explore how to utilize FFmpeg’s capabilities, alongside scripting solutions, to satisfy this requirement.

## **Understanding the Need for Binary Filename Patterns**

The desire to create filenames that use fixed-width binary patterns arises from a need for highly granular control over video segments and their retrieval. The conventional timestamp-based approaches, while useful, do not always provide the desired level of precision for filtering or processing specific durations within a video recording. A binary pattern, where each bit represents a specific time unit, allows for filtering based on the bitwise value of a number, offering a more flexible approach for selecting and managing video segments.

### **Granular Control through Binary Filenames**

Consider the provided example:

0000.ts 0001.ts … 1111.ts


This pattern, where each filename represents a 1-second chunk, enables precise selection of video segments based on the binary representation. This allows for operations such as:

*   `ls 111*.ts` to retrieve the segments starting at the 14th second (binary 1110).
*   `ls 10*.ts` to fetch segments starting at the 8th second (binary 1000).

This fine-grained control allows for powerful video processing, which could include analyzing short bursts of events in a video recording, extracting specific durations, or implementing custom video editing operations.

### **Limitations of Timestamp-Based Approaches**

While the `-strftime` option within FFmpeg provides time-based filenames (e.g., using Unix timestamps), these filenames inherently use base-10 representations, limiting the ability to quickly filter on ranges based on powers of two. Furthermore, the granularity is restricted to the resolution supported by the timestamping mechanism.

## **Challenges in Implementing Binary Filename Patterns with FFmpeg**

Directly integrating a binary representation generator into FFmpeg's native filename formatting capabilities is not straightforward. FFmpeg's `%s` or `-strftime` options provide access to timestamps and date-time strings but lack the direct capability to translate these into fixed-width binary representations. The primary hurdle involves transforming a time-based value into a binary string and integrating it with FFmpeg's filename construction tools.

### **FFmpeg's Native Filename Options**

FFmpeg's capabilities include options like:

*   `-strftime`:  This flag enables formatted timestamps in filenames. It relies on `strftime` directives to generate date and time based information.
*   `%s`:  This offers the Unix timestamp as a decimal number.

However, FFmpeg doesn't natively provide a mechanism to convert timestamps into binary, limiting the generation of fixed-width binary digits.

### **The Need for External Scripting**

Given the limitations of native FFmpeg functionality, generating fixed-width binary filenames necessitates an external scripting solution. This script will take a base-10 time value (typically a Unix timestamp, or a derived second count), convert it to a binary string, pad it to the specified width, and then incorporate this binary string into the filename. This script will effectively act as a preprocessor, providing the desired binary strings that FFmpeg can then use to create its output files.

## **Solution: Combining FFmpeg with Shell Scripting**

The solution centers on a shell script that computes the binary representation of a given time value and then utilizes this within an FFmpeg command. We will explore a Bash-based approach for generating and incorporating binary filenames into FFmpeg's recording process.

### **The Bash Script for Binary Conversion**

The core of the solution is a Bash script responsible for taking a numerical input (e.g., a Unix timestamp or a derived second count), converting it to a binary string, and formatting it.

```bash
#!/bin/bash

# Input timestamp (or any base-10 integer representing time units)
timestamp=$1

# Desired bit width (e.g., for 4-bit: 0000 to 1111)
bit_width=$2

# Convert to binary
binary_value=$(printf "%${bit_width}b" "$timestamp")

# Output the binary string
echo "$binary_value"

Explanation of the Script:

  1. Input Parameters:

    • timestamp: The numerical input (e.g., a Unix timestamp) provided via command-line argument ($1).
    • bit_width: The desired width in bits for the binary representation, supplied via command line argument ($2).

  2. Binary Conversion:

    • printf "%${bit_width}b" "$timestamp": This uses printf to convert the provided $timestamp to its binary form using the %b format specifier. The ${bit_width} controls the output field width, ensuring the output always has the desired number of bits.

  3. Output:

    • echo "$binary_value": The script outputs the generated binary string.

Integrating the Script with FFmpeg

To integrate the binary filename generation with FFmpeg, we utilize the output of the shell script. This will involve using command substitution to insert the script’s output into the FFmpeg command.

#!/bin/bash

# RTSP stream URL
rtsp_url="rtsp://10.42.0.128:554/stream1"

# Output directory
output_dir="/mnt/recordings"

# Desired segment time (in seconds)
segment_time=1

# Desired bit width (4 bits in this example)
bit_width=4

# Start a loop to generate the video segments

# Determine start time. Assuming an external script controls the timing loop
start_time=$(date +%s)

while true; do

    # Calculate current time - start time in seconds, to be used as the timestamp to convert to binary.
    time_since_start=$(( $(date +%s) - start_time ))

    # Generate the binary filename using the shell script
    binary_filename=$(./binary_converter.sh "$time_since_start" "$bit_width")

    # Construct the full output filename
    output_filename="$output_dir/$binary_filename.ts"

    # Run FFmpeg
    ffmpeg \
      -i "$rtsp_url" \
      -c copy \
      -f segment \
      -segment_time "$segment_time" \
      -reset_timestamps 1 \
      -segment_format mpegts \
      "$output_filename"

    # Wait for segment_time seconds (to avoid overlap and ensure correct filenames)
    sleep "$segment_time"

done

Explanation of the Script:

  1. Configuration: The script begins with configuration variables for the rtsp_url, output_dir, segment_time, and bit_width.

  2. Timestamp Calculation: The start time is stored. The script then calculates the seconds since the start. This number will be the timestamp for binary conversion.

  3. Filename Generation:

    • binary_filename=$(./binary_converter.sh "$time_since_start" "$bit_width"): This executes the binary_converter.sh script, using time_since_start as the timestamp and bit_width to determine the output length and capturing the binary representation into the binary_filename variable.
    • output_filename="$output_dir/$binary_filename.ts": The script assembles the full output filename by combining the output directory, the generated binary string, and the “.ts” file extension.

  4. FFmpeg Execution:

    • The ffmpeg command is invoked, configured to copy the stream (-c copy), output to segments (-f segment), use the specified segment_time, reset timestamps (-reset_timestamps 1), use mpegts format and, crucially, writes to the output_filename variable.

  5. Timing and Looping: The script will sleep for the set segment_time to create another segment.

Running the Scripts

  1. Save the scripts: Save the binary_converter.sh and the main recording script to suitable locations (e.g., in the user’s home directory or a project directory). Make the main script executable.

  2. Make the scripts executable: Use chmod +x binary_converter.sh and chmod +x recording_script.sh.

  3. Execute the main script: Run ./recording_script.sh to start the process. This command will continuously generate and record video segments based on the defined binary pattern.

Example Output

The output filenames generated will resemble the following (assuming bit_width=4 and segment_time=1):

/mnt/recordings/0000.ts
/mnt/recordings/0001.ts
/mnt/recordings/0010.ts
/mnt/recordings/0011.ts
/mnt/recordings/0100.ts
/mnt/recordings/0101.ts
...

Advanced Considerations and Optimizations

The fundamental approach discussed provides a solid foundation, but various enhancements and refinements can be applied to increase robustness and efficiency.

Error Handling

Implementing robust error handling is critical in any production environment. The script should include error checks to handle potential issues, such as:

  • FFmpeg Failure: Check the exit code of the ffmpeg process. If non-zero, it indicates an error. The script can log the error, retry the command, or halt, depending on the error severity.
  • Input Validation: Verify that the input timestamp and bit width are valid.
  • File I/O Errors: Handle potential errors when writing to the output file.

Concurrency and Optimization

Generating and writing the next binary filename while FFmpeg is still processing the last segment can be optimized through background processes. This can be achieved using & to run the FFmpeg command in the background and use a sleep, or using a more sophisticated approach to manage parallel operations.

Timestamp Source and Synchronization

The example utilizes a simple Unix timestamp for generating the sequence of binary values. Consider these points:

  • Precision: The scripts use the timestamp from the system clock. This will not be as precise as an external source of clock timing.
  • Synchronization: If using multiple capturing instances or devices, consider a time synchronization protocol (like NTP) to guarantee timestamp accuracy and consistency across the system.

File Cleanup and Management

Given that you are generating an extensive number of video segments, implementing automated file management practices is recommended:

  • Disk Space Management: Monitor disk space utilization and automatically delete older segments.
  • Rotation and Archiving: Implement a rotation strategy for segment files, periodically moving older files to an archive location.

Customizing the segment_time

The segment_time variable determines the length of each video segment. The binary filename pattern’s bit width determines the number of bits available to identify the binary values, or the amount of seconds the recording will capture. The script is designed such that the generated filename is incremented as a function of segment_time. The script can be easily adapted to use other segments.

Conclusion

By integrating FFmpeg with a shell script that generates binary filenames, we have developed a robust and flexible solution for creating video segments with a granular and highly controllable naming scheme. This allows for a high degree of precision in filtering and processing video footage. These principles can be applied to manage and analyze video recordings, giving you unparalleled power in handling your media content.