Why are videos without cut out contents are much bigger than the original video?

Help/How To
1

Hello dear Friends,

to be honest,i’m very new to the whole cutting topic.
But my programming skills are great and maybe i can contribute in the development in time.
But i have to understand the basics first and so i have a question about the exported output of a video from which i cut off just the first 5 minutes.

If you are interested, i donwloaded the following 01:01:45 lasting video in HD quality, that you can reproduce it, if you like:

The properties of the downloaded video say this (i have to translate the property names from german):

Video:
length: 01:01:45
width 1280
height 720
bit rate (or data rate): 876 kBit/s
overall bit/data rate: 1001 kBit/s
single frame rate 30 frames/second

Audio:
Bitrate: 125 kBit/s
channels: 2 (stereo)
samplerate: 44 kHz

Once opened in ShotCut, i can see some of the above mentioned properties, some not and some new ones:

Video:
Track: 1: 1280:720 h264 (the selected one)
( 2: 480x360 mjpeg ) (not selected)
Codec: H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
Resolution: 1280x720
Framerate: 30
Format: yuv420p
width-to-height-ration 16 : 9
(and two others)

Audio:
Track 1: 2 ch 44.1 kHz aac
Codec: AAC
Channels: 2
Samplerate: 44100
Format: fltp

I cut off the first round about 5 Minutes and am going to export it.
In the Export setup window i see roughly the same Video settings and 3 more properties or methods to choose from.

I leave the “Codec” tab with the default settings ( hoping that this is the same as the original ones)

But then the “Audio” tab does really surprise me:

Samplerate is set to 48000 Hz, so i set it to 44100 Hz (as in the original video)
Bitratemode (don’t know what that is, but let it as suggested) AVR
Bitrate is set to 384k and i set it down to 128k, because the original said 125k in the files properties dialog.

The original video file size is 465.640.228 Bytes
The exported vid fiile size is 639.534.521 Bytes

What?
I cut something off, but the cutted product is bigger?

And the file properties now say:

Video:
length: 00:56:26
width 1280
height 720
bit rate (or data rate): 1376 kBit/s
overall bit/data rate: 1502 kBit/s
single frame rate 30 frames/second

Audio:
Bitrate: 126 kBit/s
channels: 2 (stereo)
samplerate: 44 kHz

So, the Audio seems to be nearly the same, but how come the much higher bitrate of the video?
And what can i do to achieve the same bitrate as the original?

This result really confuses me at the moment.
So, if you are not bored by this qustion and have some time to answer or point me to the docs which explain this behavior, it would be very great.

Thank you in advance,

richard

2

It is larger due to the increased bit rate of the video track… Original 876k vs New 1376k.

3

Helo Sir,

thank you very much for your reply to my stupid question.

I do understand that the higher bitrate leads to a bigger file.
But I cannot understand how this comes?
When all the video settings are the same, why is the bitrate that much higher than that of the input file?

Can the engine be forced to use the same bitrate for output, if all the other settings are unchanged?

Thank you very much in advance,

richard

4

Well without really knowing what those settings were, it was probably encoded with some type of crf value.

In order to keep the original bitrate, you would select ABR (Average Bit Rate) and change it to the value you want.

Keep in mind… You are recompressing a compressed source, which will probably reduce the quality of the video.

5

Thank you very much, dear MrCorleone,

i believe i’ve found it now.
There is a (i have to translate it from german) “Bitratemode” with 3 choices on the “Codec” tab.

The 3 choices are
Average (AVR) (I think, that is what you pointed me to, right?)
Costant (CBR)
Qualitybased (VBR)

The default was at VBR and so i think, that produced this massiv amount of data.
I can choose the bitrate now.
That’s what i was looking for and did not find it without your help.

Thank you very, very much, dear Friend.

richard