Remuxing MPEG-TS to MKV question

[Path not found]

Hi

I'm still learning so bear with me. There is something I'm a bit confused about. I've used mkvmerge to remux an MPEG-TS file to MKV and I see there is a huge decrease in file size. I thought remuxing was just changing containers as nothing is being re-encoded, or have I got it wrong?
I also noticed the MKV output file says the bitrate is decreased, am I losing quality?

I've included the mediaInfo details for both files.

MPEG-TS file: 5.71 GB
MKV file: 3.69 GB

Does this look right?

Format                      : MPEG-TS
File size                   : 5.71 GiB
Duration                    : 43mn 54s
Overall bit rate mode       : Variable
Overall bit rate            : 18.6 Mbps

Video
ID                          : 512 (0x200)
Menu ID                     : 1 (0x1)
Format                      : AVC
Format/Info                 : Advanced Video Codec
Format profile              : High@L4
Format settings, CABAC      : Yes
Format settings, ReFrames   : 2 frames
Format settings, GOP        : M=1, N=15
Codec ID                    : 27
Duration                    : 43mn 54s
Bit rate mode               : Constant
Bit rate                    : 17.8 Mbps
Width                       : 1 920 pixels
Height                      : 1 080 pixels
Display aspect ratio        : 16:9
Frame rate                  : 25.000 fps
Color space                 : YUV
Chroma subsampling          : 4:2:0
Bit depth                   : 8 bits
Scan type                   : Interlaced
Scan order                  : Top Field First
Bits/(Pixel*Frame)          : 0.343
Stream size                 : 5.31 GiB (93%)
Color range                 : Limited
Color primaries             : BT.709
Transfer characteristics    : BT.709
Matrix coefficients         : BT.709

Audio
ID                          : 4112 (0x1010)
Menu ID                     : 1 (0x1)
Format                      : MPEG Audio
Format version              : Version 1
Format profile              : Layer 2
Codec ID                    : 3
Duration                    : 43mn 54s
Bit rate mode               : Constant
Bit rate                    : 384 Kbps
Channel(s)                  : 2 channels
Sampling rate               : 48.0 KHz
Compression mode            : Lossy
Stream size                 : 121 MiB (2%)
Language                    : English

-------

Format                      : Matroska
Format version              : Version 4 / Version 2
File size                   : 3.69 GiB
Duration                    : 43mn 54s
Overall bit rate mode       : Constant
Overall bit rate            : 12.0 Mbps
Writing application         : mkvmerge v8.2.0 ('World of Adventure') 64bit

Video
ID                          : 1
Format                      : AVC
Format/Info                 : Advanced Video Codec
Format profile              : High@L4
Format settings, CABAC      : Yes
Format settings, ReFrames   : 2 frames
Format settings, GOP        : M=1, N=15
Codec ID                    : V_MPEG4/ISO/AVC
Duration                    : 43mn 54s
Bit rate mode               : Constant
Bit rate                    : 11.4 Mbps
Nominal bit rate            : 17.8 Mbps
Width                       : 1 920 pixels
Height                      : 1 080 pixels
Display aspect ratio        : 16:9
Frame rate mode             : Constant
Frame rate                  : 25.000 fps
Color space                 : YUV
Chroma subsampling          : 4:2:0
Bit depth                   : 8 bits
Scan type                   : Interlaced
Scan order                  : Top Field First
Bits/(Pixel*Frame)          : 0.220
Stream size                 : 3.50 GiB (95%)
Default                     : Yes
Forced                      : No
Color range                 : Limited
Color primaries             : BT.709
Transfer characteristics    : BT.709
Matrix coefficients         : BT.709

Audio
ID                          : 2
Format                      : MPEG Audio
Format version              : Version 1
Format profile              : Layer 2
Codec ID                    : A_MPEG/L2
Codec ID/Hint               : MP2
Duration                    : 43mn 54s
Bit rate mode               : Constant
Bit rate                    : 384 Kbps
Channel(s)                  : 2 channels
Sampling rate               : 48.0 KHz
Compression mode            : Lossy
Stream size                 : 121 MiB (3%)
Language                    : English
Default                     : Yes
Forced                      : No

[poisondeathray]

Probably something is wrong. Typical transport stream overhead is usually about 5-8%. That size is too small

Even mediainfo reports video stream size is wrong 3.5GiB vs. 5.31GiB

But a rare possibility is that your source TS was heavily padded (filler muxing for CBR) - in that case mediainfo is incorrect . You can demux both videos and compare the stream sizes to be sure

[KarMa]

If MKVMerge did not give any error warnings then I would say it is just the padding and inefficiency of .TS, assuming this is a broadcast source. MKVMerge is usually pretty good at giving errors on stream errors and irregularities. So if there were no errors, and the MKV plays well then I would think it's fine.

Also the new MKV lists

Bit rate : 11.4 Mbps
Nominal bit rate : 17.8 Mbps

The nominal is the same bitrate as the .TS. Broadcast streams have to fill the entire available bandwidth, even if it's with filler blank data. I've had decent luck with simply compressing MPEG2/.TS videos with 7zip giving me ~10% savings.

MKVMerge certainly is not re-encoding anything.

[Path not found]

Thank you guys. No errors were reported in mkvmerge during remuxing. This was a satellite feed straight from the truck intended for the broadcaster, if that makes any difference.

'Nominal bit rate' was going to be my next question, but @KarMa has cleared this up.

[poisondeathray]

The way to check it is to demux both and compare the stream size (e.g. tsmuxer for the ts and gmkvextract for the mkv). For example mkvmerge might have aborted on an error, truncating the stream (it doesn't necessarily have to report the error)

It's very suspicious because that's massive amount of padding. 5-8% is typical. That is 10x the usual amount.

Also, there might be other streams that mediainfo isn't reporting to make up that physical size

[KarMa]

Should update mkvmerge, just because.