[FFmpeg-user] Question about file size changes

[Moritz Barsnick]

On Tue, Jun 18, 2019 at 10:25:45 +0000, David Shuman wrote:
>  From what I understand, I am doing a copy that should not alter the
> original content except to add dropped frames as necessary to sync
> the video and audio due to transmission errors.

That's correct. That's also what is happening. The stream's bandwith /
bitrate is not changed. But what ffmpeg does (by nature) is to remux,
and muxing adds overhead. This may be more or less depending on how
ffmpeg is implemented, but also depending on the target format.

>  Why is  the KB/S changing and by two different values depending solely on the suffix for the files.

If you use the suffix .m2ts, ffmpeg muxes the resulting file as M2TS,
otherwise as MPEG-TS. The difference is - as far as I can tell - that
each packet gets an additional header in M2TS mode.

See your own info:
> MEDIAINFO for original file
[...]
> Complete name                            : D:\Dave\Videos\010-raw\mts\Charge-05082019-2255.mts
> Format                                   : BDAV
> Format/Info                              : Blu-ray Video
> File size                                : 1.87 GiB
[...]
> Overall bit rate                         : 2 064 kb/s
> Video
[...]
> Bit rate                                 : 1 778 kb/s

> Mediainfo for output (MTS)
[...]
> Complete name                            : D:\Dave\Videos\020-fix\mts\Charge-05082019-2255.mts
> Format                                   : MPEG-TS
> File size                                : 1.92 GiB
[...]
> Overall bit rate                         : 2 116 kb/s
> Video
[...]
> Bit rate                                 : 1 817 kb/s

> M2TS output MediaINFO
[...]
> Complete name                            : D:\Dave\Videos\020-fix\m2ts\Charge-05082019-2255.m2ts
> Format                                   : BDAV
> Format/Info                              : Blu-ray Video
> File size                                : 1.96 GiB
[...]
> Overall bit rate                         : 2 161 kb/s
> Video
> Bit rate                                 : 1 870 kb/s

The overall size isn't so much different (2%), and due to what I
explained above.

I don't know why mediainfo determines different video bit rates (1817 vs.
1870), ffmpeg claims to have copied exactly the same amount of video
into the target containers. I don't trust mediainfo on this.

>  Which conversion is more valid in this case?  MTS or M2TS?

Valid as what? What are you trying to achive?

Cheers,
Moritz