Complex Filtering
Complex Filtering with FFmpeg¶
Introduction to FFmpeg's Filter System¶
FFmpeg's versatility and power largely stem from its comprehensive filter system, allowing for complex video and audio processing. The typed-ffmpeg library maintains this capability, providing a user-friendly interface for applying various filters.
Applying Basic Filters¶
Below is an example of how to trim a video and add a text watermark using FFmpeg's filter functions:
%xmode Minimal
import ffmpeg
# Initialize the input stream from a video file
input_stream = ffmpeg.input('input.mp4')
# Apply trimming and drawtext filters, then output to a new file
(
input_stream
.trim(start=10, end=20)
.drawtext(text='Hello World', fontsize=12, x=10, y=10)
.output(filename="output.mp4")
)
This operation is visualized in the accompanying diagram, illustrating the workflow of trimming a video and adding a watermark.
Handling Stream Types with FFmpeg¶
Understanding Typed Filters in FFmpeg¶
FFmpeg classifies its filters based on the type of media stream they process: some are intended for video streams, while others are for audio streams. This type-specific approach ensures that each filter operates on the appropriate kind of data. The typed-ffmpeg library enforces this classification through both static type checking (compatible with tools like mypy) and runtime validation, minimizing errors and streamlining filter application.
Example: Applying Filters Correctly by Stream Type¶
Consider the following code where we initialize an input stream and apply different filters:
import ffmpeg
# Initialize an input stream from a video file
input1 = ffmpeg.input('input1.mp4') # The input stream here is an AVStream, capable of handling both audio and video operations.
# Apply a reverse filter, which is specifically a video filter, to the stream
video = input1.reverse() # The 'reverse' filter is applied, resulting in a VideoStream output.
# Attempting to apply an audio filter (amix) to a video stream results in an error
ffmpeg.filters.amix(video) # This line will raise an exception because 'amix' is an audio filter, incompatible with a VideoStream.
In this example, the reverse filter, which is designed for video streams, successfully transforms the input into a reversed video stream. However, when attempting to apply the amix filter, which is intended for audio streams, to the reversed video stream, the code will raise an exception. This error occurs because typed-ffmpeg recognizes the mismatch between the stream type (video) and the expected input type for the amix filter (audio).
By incorporating these type checks, typed-ffmpeg aids in preventing common mistakes, such as applying an audio filter to a video stream or vice versa, thereby ensuring that filters are applied correctly and efficiently.
Working with Multiple Inputs¶
Certain filters accept multiple inputs. When using such filters with typed-ffmpeg, ensure that the exact number of required streams is passed, as validated by static type checking:
import ffmpeg
# Initialize two input streams
input1 = ffmpeg.input('input1.mp4')
input2 = ffmpeg.input('input2.mp4')
# Overlay one stream over the other and output to a new file
(
input1
.overlay(input2, x=10, y=10)
.output(filename="output.mp4")
)
The process of overlaying two video streams is illustrated in the diagram:
Handling Multiple Outputs¶
Some filters, when applied, generate multiple output streams. typed-ffmpeg facilitates handling these scenarios with clear and concise code:
import ffmpeg
# Initialize input streams
input1 = ffmpeg.input('input1.mp4')
input2 = ffmpeg.input('input2.mp4')
# Apply a filter that generates multiple outputs
video, feedout = input1.feedback(input2) # Generates two output streams
# Process and output each stream separately
o1 = video.drawtext(text='Hello World', fontsize=12, x=10, y=10).output(filename="output1.mp4")
o2 = feedout.drawtext(text='Hello World', fontsize=12, x=10, y=10).output(filename="output2.mp4")
# Merge the outputs
ffmpeg.merge_outputs(o1, o2)
The generation of multiple output streams from a single filter application is depicted:
Dynamic Input Filters¶
Some filters accept a variable number of inputs. In these cases, typed-ffmpeg offers flexibility but requires careful input management:
import ffmpeg
# Correct usage with the expected number of inputs
input1 = ffmpeg.input('input1.mp4')
input2 = ffmpeg.input('input2.mp4')
ffmpeg.filters.amix(input1, input2, inputs=2)
Incorrect input numbers will trigger exceptions, providing immediate feedback without needing to execute FFmpeg:
import ffmpeg
# Incorrect usage leading to a ValueError
input1 = ffmpeg.input('input1.mp4')
input2 = ffmpeg.input('input2.mp4')
f = ffmpeg.filters.amix(input1, input2, inputs=3) # This will raise a ValueError
Fortunately, typed-ffmpeg offers automatic detection for input variables in many of ffmpeg's dynamic input filters.
import ffmpeg
input1 = ffmpeg.input('input1.mp4')
input2 = ffmpeg.input('input2.mp4')
ffmpeg.filters.amix(input1, input2) # typed-ffmpeg will auto detect the correct inputs value
Dynamic Output Filters¶
Similarly, some filters yield a dynamic number of outputs. typed-ffmpeg ensures that any mismatches are quickly identified:
import ffmpeg
# Initialize input and apply a split filter
input1 = ffmpeg.input('input1.mp4')
split = input1.split(outputs=2)
# Correctly accessing the outputs
video0 = split.video(0)
video1 = split.video(1)
# Incorrectly accessing an out-of-range output will raise an error
video2 = split.video(2) # This will raise a ValueError