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I want to change AR, do I have to re-encode? If so, how can I keep original settings?

3 Replies, 819 Views

Let’s say I have one m2ts file (AR 1.78:1) and all I want to do is change the AR to 1.85:1 (black bars on the top and bottom 22px each). Is there any software that allows me to do this without re-encoding? I suppose not.

Therefore, I want to see all the video properties of the m2ts file. What software can I use to view all the original parameters? I mean, all the parameters I must keep to obtain a new m2ts file identical to the original file.

What software can I use to preserve all of them? I normally use Adobe Premiere.
Black bars are usually part of the video in BD compliant streams. You can always change aspect ratio in mkvmerge or some such but that doesn’t add “true” black bars. In order to get them there permanent you have to re-encode as far as I know. You should be able to do that in AP by adding crop at the top and bottom or changing the project’s aspect ratio

I use mediainfo for viewing video files properties.
Easy and fastest way to do that is to use a player that will overlay black bars for you. Wink

Second easy way: feed it to VirtualDub2 and use an internal filter to crop and then add black bars.
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I have used Mediainfo. Are these all the parameters I need for the new copy to be identical?:


ID                                      : 4113 (0x1011)
Menu ID                                  : 1 (0x1)
Format                                  : AVC
Format/Info                              : Advanced Video Codec
Format profile                          : [email protected]
Format settings                          : CABAC / 4 Ref Frames
Format settings, CABAC                  : Yes
Format settings, ReFrames                : 4 frames
Codec ID                                : 27
Duration                                : 1 h 26 min
Bit rate mode                            : Variable
Bit rate                                : 19.1 Mb/s
Maximum bit rate                        : 30.0 Mb/s
Width                                    : 1 920 pixels
Height                                  : 1 080 pixels
Display aspect ratio                    : 16:9
Frame rate                              : 23.976 (24000/1001) FPS
Standard                                : NTSC
Color space                              : YUV
Chroma subsampling                      : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                      : 0.383
Stream size                              : 11.5 GiB (83%)
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                : BT.709
Matrix coefficients                      : BT.709

Well, take a look at this very interesting information I have found:


Use a bitstream filter

The h264_metadata and hevc_metadata bitstream filters can set crop dimensions without modifying the video itself.
Note: Your player may not support this method.



Set the frame cropping offsets in the SPS. These values will replace the current ones if the stream is already cropped.
These fields are set in pixels. Note that some sizes may not be representable if the chroma is subsampled or the stream is interlaced (see H.264 section

I have never used FFmpeg. but if I understand correctly, can I change the aspect ratio of one m2ts file without re-encoding only if that m2ts is already cropped?

Two examples:

-1.78:1 to 1.85:1, is it not possible since the 1.78:1 is not cropped?

-1.85:1 to 2.35:1, is it possible since 1.85:1 is already cropped?
(This post was last modified: 2021-07-14, 06:33 PM by Onti.)

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