Lesson 3 · 20 min
Editing is deciding where each shot starts and ends, how one passes into the next and what is read on screen. In this lesson you edit the four rehearsal clips from the batch in a free editor, add captions and check the exported file right here on the page.
Start the lesson
Goal: cut and link the clips into a 12 to 20 s cut in 16:9, with captions, and check the exported file on the page.
Six steps on the timeline. Tap each one.
An editing problem gets fixed in the editor, not by generating again: reordering, trimming and swapping the transition cost no credits.
With the four rehearsal clips from the batch (link in the practice) or with your own.
The example uses Concat (0.2.7 beta, Oct/2026): an open-source video editor (AGPL-3.0 license), installed on your computer, with no account, no subscription and no watermark. It runs on Windows, macOS, Linux and Android.
Since it's a beta, it still has rough edges, and the installers aren't signed: on Windows, the warning asks for "More info › Run anyway". If you already use another editor, the steps are the same.
Drag the clips into the order of your edit plan. Trim half a second at the start and end of each generated clip and watch the whole sequence at once, to feel the rhythm.
If a shot feels long, it is: cut until the action is clear and nothing more. Vary the shot size between neighbors, as the shot list asked.
Hard cut by default. Short dissolve when time passes. Match on action: cut in the middle of a movement and continue the movement in the next shot.
J-cut: the sound of the next shot comes in before the image (the knocks at the door before you see the door). L-cut: the sound of the shot continues after the cut. Both connect shots without a visual effect.
The three knocks start at the end of the oven shot (J-cut) and the cut to the door comes on the third knock.
Concat generates captions with Whisper running on your computer: download the models once in Settings › Models. Check proper names and numbers before you burn in the captions.
Export as MP4 H.264, 16:9. HEVC and AV1 save space, but not every browser opens them: to check here, prefer H.264.
INEMA video (10/15/2026) about Concat. Vertical short, with captions.
A cut list to write down your editing decisions before you touch the editor.
Edit: <name> (<target duration> s, 16:9) # n | clip | in at | out at | transition to the next | sound 1 | plano-1 | <s> | <s> | hard cut | clip ambience 2 | plano-2 | <s> | <s> | J-cut (the sound of 3 comes in early) | <...> Captions: <yes or no; reviewed?> Export: MP4 H.264, <width>×<height>
Choose the exported MP4. The page reads the duration and size in your browser; nothing is uploaded. First try the example that passes and the example with an error.
Choose your video. It is read here in the browser: nothing is uploaded.
Only for people who already use a terminal and have ffmpeg installed (the checker uses ffprobe). Run it in the course folder you downloaded from GitHub; for your own file, replace --exemplo with its name (montagem.mp4).
python3 conferir.py montagem --exemplo; echo "saída: $?" python3 conferir.py montagem --errado; echo "saída: $?"
$ python3 conferir.py montagem --exemplo; echo "saída: $?" OK: 15,0 s · 1280×720 · 16:9 saída: 0
$ python3 conferir.py montagem --errado; echo "saída: $?" Ainda não. O que falta: - O vídeo tem 8,0 s; o pedido é de 12 a 20 s. - O vídeo é 720×1280 (9:16); o pedido é 16:9. - O vídeo tem 720 px de largura; o mínimo é 1280 px. saída: 1
Assemble the four rehearsal clips (or your own) in 16:9, with hard cuts and at least one J-cut or L-cut, and export as MP4 H.264. Choose the file in "Check your assembly" and save it in the project folder as montagem.mp4.
Done when: the page answers OK: [s] s · [w]×[h] · 16:9, with a duration between 12 and 20 s and a width of at least 1280 px.
Write one sentence of narration for the assembly, record it in your own voice, and generate the subtitles in the editor. Proofread them and export again with the subtitles burned in; in the final film (lesson 8), the subtitles go in after the color.
Done when: the page keeps answering OK: … for the new file and, when you play the video, the subtitles show on screen with the words you recorded.
Four questions. The explanation appears after each answer.
Question 1 of 4
A generated shot has a distortion in its last 10 frames. What do you do first?
Question 2 of 4
The knocks at the door start to sound at the end of the oven shot, before the cut to the door. Which cut is this?
Question 3 of 4
Why export as MP4 H.264 to check it on the page?
Question 4 of 4
The page answers "O vídeo é 1080×1920 (9:16); o pedido é 16:9". What happened?
Choose an answer. The explanation appears after you try.