How to fix the ffmpeg python issue "Error applying option 'original_size' to filter 'ass': Invalid argument"?

Question

ENVIRONMENT:

Python 3.10

Windows 11

ffmpeg-python==0.2.0

CONTEXT:

I am trying to add hardcoded subtitles on a video with ffmpeg and Pyton.

PROBLEM:

ffmpeg is not able to find the path of my ass subtitle file. So I tried different ways with different methods. I asked different AI to try to find a solution. Impossible! It is such a crazy issue that I tested the code from a "test" folder located on the root "C:" from the command line wid nows. No AI was able to fixed this issue. I tried chatGPT, deepseek, claude.ai. They proposed different solutions which were not working.

THE CODE :

import os
import ffmpeg
import subprocess

def add_subtitles_with_ass(video_path, ass_path, output_path):

    video_path = os.path.abspath(video_path)
    ass_path = os.path.abspath(ass_path)
    output_path = os.path.abspath(output_path)

    print(f"🚀 Add susbtitiles with ASS : {ass_path}")
    ass_path_escaped = rf'"{ass_path}"'

    try:
        ffmpeg.input(video_path).output(output_path, vf=f"ass='{ass_path_escaped}'").run(overwrite_output=True)
        print(f"✅ Subtitles added with success : {output_path}")
    except Exception as e:
        print(f"❌ ERROR when adding subtitles : {e}")


def add_subtitles_with_ass_with_subprocess(video_path, ass_path, output_path):
    video_path = os.path.abspath(video_path)
    ass_path = os.path.abspath(ass_path)
    output_path = os.path.abspath(output_path)

    print(f"🚀 Add subtitles with ASS : {ass_path}")

    try:
        command = [
            'ffmpeg',
            '-i', video_path,
            '-vf', f"ass='{ass_path}'",
            '-c:a', 'copy',
            output_path,
            '-y'  # Overwrite output file without asking
        ]

        subprocess.run(command, check=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        print(f"✅ Subtitles added with success : {output_path}")
    except subprocess.CalledProcessError as e:
        print(f"❌ ERROR when adding subtitles : {e.stderr.decode('utf-8')}")


print(f"Test 1 -----------------------------------------------------------------------")
ass_path="G:\Mi unidad\Python\Scripts\shorts_videos\10000views_and_higher\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.ass"
video_path="G:\Mi unidad\Python\Scripts\shorts_videos\10000views_and_higher\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo.mp4"
output_path="G:\Mi unidad\Python\Scripts\shorts_videos\10000views_and_higher\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.mp4"
add_subtitles_with_ass(video_path, ass_path, output_path)
print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 2 -----------------------------------------------------------------------")
ass_path2="G:\\Mi unidad\\Python\\Scripts\\shorts_videos\\10000views_and_higher\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.ass"
video_path2="G:\\Mi unidad\\Python\\Scripts\\shorts_videos\\10000views_and_higher\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo.mp4"
output_path2="G:\\Mi unidad\\Python\\Scripts\\shorts_videos\\10000views_and_higher\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.mp4"
add_subtitles_with_ass(video_path2, ass_path2, output_path2)

print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 3 -----------------------------------------------------------------------")
ass_path3="G:/\Mi unidad/\Python/\Scripts/\shorts_videos/\10000views_and_higher/\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.ass"
video_path3="G:/\Mi unidad/\Python/\Scripts/\shorts_videos/\10000views_and_higher/\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo.mp4"
output_path3="G:/\Mi unidad/\Python/\Scripts/\shorts_videos/\10000views_and_higher/\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.mp4"
add_subtitles_with_ass(video_path3, ass_path3, output_path3)

print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 4 -----------------------------------------------------------------------")
ass_path4="G:/\\Mi unidad/\\Python/\\Scripts/\\shorts_videos/\\10000views_and_higher/\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.ass"
video_path4="G:/\\Mi unidad/\\Python/\\Scripts/\\shorts_videos/\\10000views_and_higher/\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo.mp4"
output_path4="G:/\\Mi unidad/\\Python/\\Scripts/\\shorts_videos/\\10000views_and_higher/\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.mp4"
add_subtitles_with_ass(video_path4, ass_path4, output_path4)




print(f"Test 1 with subprocess -----------------------------------------------------------------------")
add_subtitles_with_ass_with_subprocess(video_path, ass_path, output_path)
print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 2 with subprocess -----------------------------------------------------------------------")
add_subtitles_with_ass_with_subprocess(video_path2, ass_path2, output_path2)
print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 3 with subprocess -----------------------------------------------------------------------")
add_subtitles_with_ass_with_subprocess(video_path3, ass_path3, output_path3)
print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 4 with subprocess -----------------------------------------------------------------------")
add_subtitles_with_ass_with_subprocess(video_path4, ass_path4, output_path4)
print(50*"*")
print(50*"*")
print(50*"*")

#======================= IT DIDN'T WORK, SO LET'S DO WITH RELATIVE PATH ===================================


print(f"Test 1 with relative path -----------------------------------------------------------------------")
ass_path_relative="10000views_and_higher\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.ass"
video_path_relative="10000views_and_higher\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo.mp4"
output_path_relative="10000views_and_higher\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.mp4"
add_subtitles_with_ass(video_path_relative, ass_path_relative, output_path_relative)
print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 2  with relative path -----------------------------------------------------------------------")
ass_path2_relative="10000views_and_higher\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.ass"
video_path2_relative="10000views_and_higher\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo.mp4"
output_path2_relative="10000views_and_higher\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.mp4"
add_subtitles_with_ass(video_path2_relative, ass_path2_relative, output_path2_relative)

print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 3  with relative path -----------------------------------------------------------------------")
ass_path3_relative="10000views_and_higher/\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.ass"
video_path3_relative="10000views_and_higher/\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo.mp4"
output_path3_relative="10000views_and_higher/\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.mp4"
add_subtitles_with_ass(video_path3_relative, ass_path3_relative, output_path3_relative)

print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 4  with relative path -----------------------------------------------------------------------")
ass_path4_relative="10000views_and_higher/\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.ass"
video_path4_relative="10000views_and_higher/\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo.mp4"
output_path4_relative="10000views_and_higher/\\Li2zY7XcOf0_Matthew_Hussey_flip_h_BW_with_logo_EN.mp4"
add_subtitles_with_ass(video_path4_relative, ass_path4_relative, output_path4_relative)




print(f"Test 1 with subprocess  with relative path -----------------------------------------------------------------------")
add_subtitles_with_ass_with_subprocess(video_path, ass_path, output_path)
print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 2 with subprocess  with relative path -----------------------------------------------------------------------")
add_subtitles_with_ass_with_subprocess(video_path2_relative, ass_path2_relative, output_path2_relative)
print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 3 with subprocess  with relative path -----------------------------------------------------------------------")
add_subtitles_with_ass_with_subprocess(video_path3_relative, ass_path3_relative, output_path3_relative)
print(50*"*")
print(50*"*")
print(50*"*")

print(f"Test 4 with subprocess  with relative path -----------------------------------------------------------------------")
add_subtitles_with_ass_with_subprocess(video_path4_relative, ass_path4_relative, output_path4_relative)
print(50*"*")
print(50*"*")
print(50*"*")

THE OUTPUT:

The output was too large to post it here. I uploaded it on my github :

https://github.com/gauthierbuttez/public/blob/master/output_ffmpeg.log

I also zipped and uploaded all the files to make reproducing the issue on your computer easy:

https://github.com/gauthierbuttez/public/blob/master/test.zip

Is there any kind super Python Master in the place?

Jukizuka · Accepted Answer · 2025-02-16 17:40:22Z

It's just a quirk of how FFmpeg expects a absolute path in the ass filter. It requires you to escape every special character because of the way it parses strings internally. The most surprising fact is that the colon (:) also needs to be escaped.

So, when passing absolute path in terminal it would look like this:

ffmpeg -i video.mp4 -vf "ass='G\:\\Shorts_videos\\Li2zY7XcOf0.ass'" -c:a copy out.mp4 -y

Because of that in Python you would need to double escape backslashes and escape colon. So absolute path in string literal would look like this in Python:

# As a normal string literal
ass_path = "G\\:\\\\Shorts_videos\\\\Li2zY7XcOf0.ass"

# It is easier to read as a raw string literal, in my opinion,
# because it looks exactly like the one passed in terminal.
# So following would also be valid:
ass_path = r"G\:\\Shorts_videos\\Li2zY7XcOf0.ass"

P.S. In other paths (for video and output), I also recommend using raw string literals. Otherwise, sequences like \t in a string might be mistakenly interpreted as a tab or another escape sequence. By prefixing the string with r, you won’t need to manually escape characters in such cases.

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