output files way too big

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1

Kdenlive is super convenient, easy to use, and robust–but I’m having a big problem with output file size. Using v. 23.08.5 to edit Zoom recordings of a few talking heads and mostly static slide presentations. No animations or any other fancy stuff of any kind. Typical Zoom mp4 for a 90 minute recording is a few hundred megabytes. Example: ls -l video.mp4 reports 138794815, and ffprobe video.mp4 says

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from ‘video.mp4’:
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: mp42isom
creation_time : 2026-07-23T21:35:38.000000Z
Duration: 01:18:08.94, start: 0.000000, bitrate: 236 kb/s
Stream #0:00x1: Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 75 kb/s (default)
Metadata:
creation_time : 2026-07-23T21:35:38.000000Z
handler_name : AAC audio
vendor_id : [0][0][0][0]
Stream #0:10x2: Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt470bg/bt470bg/bt709, progressive), 966x838, 158 kb/s, 25 fps, 25 tbr, 30k tbn (default)
Metadata:
creation_time : 2026-07-23T21:35:38.000000Z
handler_name : H.264/AVC video
vendor_id : [0][0][0][0]
encoder : AVC Coding

The proxy (640pixels wide, encoding profile ProRes) is > 5 GB! (5891709900 to be exact).

Editing was limited to some cuts that shortened the timeline by a few minutes. No fancy nothing. The rendered output MP4 file is 606642735 !, 4x bigger than the unedited original; ffprobe reports this

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from ‘finishededit.mp4’:
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf60.16.100
Duration: 01:16:27.20, start: 0.000000, bitrate: 1057 kb/s
Stream #0:00x1: Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, smpte170m, progressive), 966x838 [SAR 1:1 DAR 483:419], 891 kb/s, 25 fps, 25 tbr, 12800 tbn (default)
Metadata:
handler_name : VideoHandler
vendor_id : [0][0][0][0]
Stream #0:10x2: Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 160 kb/s (default)
Metadata:
handler_name : SoundHandler
vendor_id : [0][0][0][0]

My naive guess is the output file bitrates are too high, but what do I know. With ffmpeg I can distill the final output to generate MP4s that are not visibly different but use video bitrate of 158k and are much smaller, but why is that necessary? Can Kdenlive do it?

2

Hi @tedc, and welcome to the forum and community.

Could it be that the source files have variable FRAME rate? If, so Kdenlive needs to create frames for the fixed frame rate of the project which of course increases the file size compared to the original video.

BTW, the Kdenlive version you are using is 3 years old.

3

This is an issue with Kdenlive that I’ve had for a long time, even on the current stable release (26.04.3). Regardless of what I did (at 75% quality/CRF 23), such as using veryslow, different presets, HW encoding, the files I got from Kdenlive were unreasonably large.

A recent example of this is where I edited a ~15 minute video containing mostly still footage (tutorial type stuff). The OBS recording was recorded using VAAPI ultrafast h.264, and was ~140 MB. The edited video, using the default h.264 preset, came out as 500 MB when encoded at ultrafast and 220 MB when encoded with slow.

My temporary solution to this problem is to edit a video, render it with ultrafast, then use ffmpeg -i input.mp4 -c:v libx264 -c:a copy -preset slow -movflags +faststart output.mp4. The resulting file of the example above is <50 MB. On my potato laptop, this is much faster than anything else I’ve found, and the quality loss is nearly imperceptible.

4

I don’t use kdenlive but your size problem is reflected in the bitrates:

Before:

After:

See Video Bitrate vs Resolution: What Actually Controls File Size? | VideoCompress.io for an explanation why.

I presume kdenlive has presets for exporting and adjusting bitrates; you’ll likely need to choose one that matches or reduces the original bitrate.

5

Kdenlive is super convenient, easy to use, and robust–but I’m having a big problem with output file size. Using v. 23.08.5 to edit Zoom recordings of a few talking heads and mostly static slide presentations.

what? 3 years old build?

better to switch to a newest one because.. things changes rapidly and any suggestion from the forum is related to 26.04

6

Hi berndmj, thanks for the quick reply. Web search turns up several
discussions related to big output files that date back many years, and
some of those mention variable frame rate as the likely cause. That
said, checking my particular example file with mediainfo reports

General
. . .
Overall bit rate mode                    : Variable
Overall bit rate                         : 237 kb/s
Frame rate                               : 25.000 FPS. . . 
. . .
Video
. . . 
Frame rate mode                          : Constant
Frame rate                               : 25.000 FPS

BTW, the Kdenlive version you are using is 3 years old.

Yes, the latest version distributed by the latest version of Linux Mint (22.3). Seems to work well enough for my very pedestrian use, except for this one issue. It’s clear that Kdenlive is under very active development, with lots of maintenance releases. Do you think that file size has already been addressed in a more recent version?

7

MLT does the filters, effects, compositions, and then hands the frames over to ffmpeg for encoding. Kdenlive is always built with the latest stable versions of MLT and ffmpeg, so I would think that in the last three years a lot of things have changed and improvements made in MLT and ffmpeg.

I cannot say for sure but I what I am sure about is that it’s definitely worth a try. Use the AppImage and render your project again to see whether the issue still persists.