How can I convert an FFmpeg command line to ffmpeg-python code?

Question

I have this command-line code:

ffmpeg -i 0.mp4 -c:v libx265 -preset fast -crf 28 -tag:v hvc1 -c:a aac -bitexact -map_metadata -1 out.mkv

And I want to convert it to ffmpeg-python code in Python.

But how can I do it?

This is what I have done so far:

import ffmpeg

(
    ffmpeg
    .input('0.mp4')
    .filter('fps', fps=30)
    .output('out.mkv', vcodec='libx265', crf=28, preset='fast', movflags='faststart', pix_fmt='yuv420p')
    .run()
)

Answer 1

You may add .global_args('-report') for testing the correctness of an FFmpeg command line.

The -report argument generates a log file with a name like ffmpeg-20210715-000009.log.

One of the first text lines in the log file is the FFmpeg command line with arguments.

---

There are good ffmpeg-python examples here and here. You may also read the reference (it's not long).

---

You may use "special option names" as documented:

Arguments with special names such as -qscale:v (variable bitrate), -b:v (constant bitrate), etc. can be specified as a keyword-args dictionary as follows:
... .output('out.mp4', **{'qscale:v': 3})
...

You can use the following command (using "special names"):

(
    ffmpeg
    .input('0.mp4')
    .output('out.mkv', **{'c:v': 'libx265'}, preset='fast', crf=28, **{'tag:v': 'hvc1'}, **{'c:a': 'aac'}, **{'bitexact': None}, map_metadata='-1')
    .global_args('-report')
    .run()
)

In the reported log file the command line is:

ffmpeg -i 0.mp4 -bitexact -c:a aac -c:v libx265 -crf 28 -map_metadata -1 -preset fast -tag:v hvc1 out.mkv -report

It's the same as your posted command line except of the order of the output arguments.

---

For using less "special names", you may replace the special names with equivalent names:

• Replace: c:v with vcodec
• Replace: c:a with acodec
• Replace tag:v with vtag

There is probably a replacement for **{'bitexact': None}, but I can't find it.

---

The updated code is:

(
    ffmpeg
    .input('0.mp4')
    .output('out.mkv', vcodec='libx265', preset='fast', crf=28, vtag='hvc1', acodec='aac', **{'bitexact': None}, map_metadata='-1')
    .global_args('-report')
    .run()
)