Stretching video (changing aspect ratio)

[ddewaele]

Hi,

I have a video from a capturing device that has captured footage from an old computer (MDA graphics 720x350). The captured video file has a resolution of 1024x768 (dictated by the capturing device), but the video shows the content way too narrow (it is captured like a square, so I need to increase the width of the video somehow or change the aspect ratio).

If I load up the file in VLC player, it looks like this


[Attachment 50868 - Click to enlarge]

If I change the aspect ratio in VLC player to 16:9 it actually looks a lot better and resembles more what I see on the monitor.
So I would like to have it permanently look like that by modifying the video file itself, so other players will play it automatically like that


[Attachment 50869 - Click to enlarge]

As you can see the image is stretched out, and resembles more what I see on the monitor.

What I've tried :

- I tried using the VLC convert / stream function by changing the resolution (width / height) but it doesn't seem to change the aspect ratio.
- I've also tried using mp4muxer, but if I multiplex and change the width / height, the output file always looks exactly the same.

Any ideas how I should proceed in exporting this to a video file where it is stretched out and resembles the 16:9 playback in VLC ?

Thx a lot.

[DB83]

Ok. Better start with an upload to here of a mediainfo (text mode) report of the original .mp4

Frankly, I have never heard of any capture device that could capture at 124*768 and if your previous graphics were only 720*350 I can hardly see it capturing at more than double the vertical resolution.

[dannyboy48888]

Do you need the mp4 container? Is not drop it into mkvtoolnix and under the video tab set the appropriate aspect or display resolution

[Budman1]

https://superuser.com/questions/907933/correct-aspect-ratio-without-re-encoding-video-file

To scale the image and change SAR (while transcoding), try:

ffmpeg -i <INPUT_FILE> -vf scale=854:480 -c:v <Video_Codec> <OUTPUT_FILE>

On the other hand, if you just want to change the metadata flag and adjust the DAR, you will be able to stream copy the video. To do this, try:

ffmpeg -i <INPUT_FILE> -aspect 16:9 -c copy [OUTPUT_FILE]

-aspect[tream_specifier] aspect (output,per-stream)
Set the video display aspect ratio specified by aspect.

aspect can be a floating point number string, or a string of the form num:den, where num and den are the numerator and denominator of the aspect ratio. For example "4:3", "16:9", "1.3333", and "1.7777" are valid argument values.

[ddewaele]

Ok. Better start with an upload to here of a mediainfo (text mode) report of the original .mp4

Frankly, I have never heard of any capture device that could capture at 124*768 and if your previous graphics were only 720*350 I can hardly see it capturing at more than double the vertical resolution.

Sorry about the typo .. should have been 1024x768.

Going to add the media info.

[ddewaele]

I ended up using the following tool / command

mp4box original.mp4 -out out-4.mp4 -par 2=4:3

Here is the original file

General
Complete name                            : Y:\video\original.mp4
Format                                   : MPEG-4
Format profile                           : Base Media / Version 2
Codec ID                                 : mp42 (mp42/isom)
File size                                : 34.3 MiB
Duration                                 : 58 s 880 ms
Overall bit rate                         : 4 884 kb/s
Encoded date                             : UTC 2019-11-14 20:07:25
Tagged date                              : UTC 2019-11-14 20:07:25

Video
ID                                       : 2
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L4.1
Format settings                          : CABAC / 1 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 1 frame
Format settings, GOP                     : M=1, N=30
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 58 s 880 ms
Source duration                          : 58 s 867 ms
Bit rate                                 : 4 762 kb/s
Width                                    : 1 024 pixels
Height                                   : 768 pixels
Display aspect ratio                     : 4:3
Frame rate mode                          : Variable
Frame rate                               : 29.970 (29970/1000) FPS
Minimum frame rate                       : 20.000 FPS
Maximum frame rate                       : 30.000 FPS
Original frame rate                      : 30.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.202
Stream size                              : 33.4 MiB (97%)
Source stream size                       : 33.4 MiB (97%)
Language                                 : English
Encoded date                             : UTC 2019-11-14 20:07:25
Tagged date                              : UTC 2019-11-14 20:07:25
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709
mdhd_Duration                            : 58866
Codec configuration box                  : avcC

[Attachment 50881 - Click to enlarge]

And after executing the mp4box command above I got this file :

General
Complete name                            : Y:\video\out-4.mp4
Format                                   : MPEG-4
Format profile                           : Base Media / Version 2
Codec ID                                 : mp42 (mp42/isom)
File size                                : 34.3 MiB
Duration                                 : 58 s 888 ms
Overall bit rate                         : 4 889 kb/s
Encoded date                             : UTC 2019-11-14 20:07:25
Tagged date                              : UTC 2019-11-14 20:07:25

Video
ID                                       : 2
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L4.1
Format settings                          : CABAC / 1 Ref Frames
Format settings, CABAC                   : Yes
Format settings, Reference frames        : 1 frame
Format settings, GOP                     : M=1, N=30
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 58 s 866 ms
Source duration                          : 58 s 867 ms
Bit rate                                 : 4 762 kb/s
Width                                    : 1 024 pixels
Height                                   : 768 pixels
Display aspect ratio                     : 16:9
Original display aspect ratio            : 4:3
Frame rate mode                          : Variable
Frame rate                               : 29.970 (29970/1000) FPS
Minimum frame rate                       : 20.000 FPS
Maximum frame rate                       : 30.000 FPS
Original frame rate                      : 30.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.202
Stream size                              : 33.4 MiB (97%)
Source stream size                       : 33.4 MiB (97%)
Language                                 : English
Encoded date                             : UTC 2019-11-14 20:07:25
Tagged date                              : UTC 2019-11-15 09:13:45
Color range                              : Limited

[Attachment 50882 - Click to enlarge]

This was pretty much the visual I was looking for. So if I understand correctly only a parameter (meta-data) was changed (Display aspect ratio) and not the actual file.
But why did it end up setting 16:9 in the meta-data when I specified "-par 2=4:3" in the mp4box command ?
When I specified "-par 2=16:9" in the mp4box command the Display aspect ratio was set to 2.40:1

[jagabo]

Keep in mind that changing the flagged aspect ratio will not work with all players. Media players built into TVs, Blu-ray players, and other devices may ignore the flags.

[DB83]

Ok. Better start with an upload to here of a mediainfo (text mode) report of the original .mp4

Frankly, I have never heard of any capture device that could capture at 124*768 and if your previous graphics were only 720*350 I can hardly see it capturing at more than double the vertical resolution.

Sorry about the typo .. should have been 1024x768.

Going to add the media info.

Well I guess as much.

The mediainfo report confirms that the original video is 4:3 which also agrees to the 1024*768 (just check the maths)

It is possible that you were fooled by the display and the monitor somewhat hid the black borders that merged into the original frame.

I can not answer your Q. as to why that command should result in a 16:9 DAR. A 1024*768 4:3 should result in 1366*768 and you may wish to create a vid with those parameters. Be warned, however, that such a stretch will change the display of all text. For purely text it will not be so obvious but for general video such a stretching is not desirable.

Yet I still struggle to understand where the 1024*768 came from in the first place.