MP4 Videos Unnecessarily Encoded During Trim #233

Describe the Bug

In clip_and_reformat_video if the video is already mp4 ffmpeg will encode the output stream as mp4.

Expected Behavior

Use ffmpeg StreamCopy to avoid re-encoding an already mp4 encoded video.

Reproduction

Proof of concept with ffmpeg-python:

Existing implementation:

import ffmpeg
import os

(
    ffmpeg
    .input('big_buck_bunny_720p_surround.mp4', ss='01:00', to='02:00')
    .output('trimmed.mp4', format='mp4')
    .run()
)

os.remove('trimmed.mp4')

using time python main.py shows real ~3s. I didn't benchmark this so it's anecdotal. On my machine, the encode speed is ~20x (60 / 20 ~= 3).

Use StreamCopy:

import ffmpeg
import os

(
    ffmpeg
    .input('big_buck_bunny_720p_surround.mp4', ss='01:00', to='02:00')
    .output('trimmed.mp4', format='mp4', codec='copy')
    .run()
)

os.remove('trimmed.mp4')

(Note the only difference is codec='copy' arg in output.)

When using StreamCopy, the pipeline on my machine takes ~200ms.

Environment

• OS Version: Linux ld1 5.19.0-41-generic #42~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Tue Apr 18 17:40:00 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
• cdp-backend Version: 4.1.0.rc0