MPEG-TS to MKV (remux): Smaller File?

Hi all. I've been a long-term lurker and until now I haven't needed to post. Unfortunately that changed tonight when I attempted to remux an MPEG-TS file into an MKV. The path was a bit indirect but I eventually got there. Here's what I did:

1. TsRemux: ".mpeg" -> ".m2ts"
2. mkvmerge: ".m2ts" -> ".mkv"

Why the two-step? Well, mkvmerge threw errors when I gave it a ".mpeg" so I first had to get to an ".m2ts". That seemed to work, though mkvmerge did complain about additional bytes in the audio stream (and therefore gave a warning that the two might be out of sync). Here's the real question, though: Why is the MKV so much smaller than the M2TS? Check it out:

MPEG: 11,955,479,300 bytes (11.1 GB)
M2TS: 12,219,000,192 bytes (11.3 GB)
MKV: 9,823,195,543 bytes (9.14 GB)

That's a reduction of almost 18% (from the MPEG) with no re-encoding or element conversion as far as I can tell. Is MKV just way more efficient or am I dropping something along the way? Here's Mediainfo output for each file:


MPEG
----

General
ID : 255 (0xFF)
Complete name : C:\Video\Work\Camcorder\Tape 1.mpeg
Format : MPEG-TS
Commercial name : HDV 1080i
File size : 11.1 GiB
Duration : 1h 2mn
Start time : UTC 2008-02-01 01:00:24
End time : UTC 2008-06-07 12:55:58
Overall bit rate mode : Variable
Overall bit rate : 25.5 Mbps
Maximum Overall bit rate : 33.0 Mbps
Encoded date : UTC 2008-02-01 01:00:24

Video
ID : 2064 (0x810)
Menu ID : 100 (0x64)
Format : MPEG Video
Commercial name : HDV 1080i
Format version : Version 2
Format profile : Main@High 1440
Format settings, BVOP : Yes
Format settings, Matrix : Custom
Format settings, GOP : M=3, N=15
Codec ID : 2
Duration : 1h 2mn
Bit rate : 23.8 Mbps
Maximum bit rate : 25.0 Mbps
Width : 1 440 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate : 29.970 fps
Standard : Component
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Interlaced
Scan order : Top Field First
Compression mode : Lossy
Bits/(Pixel*Frame) : 0.511
Stream size : 10.4 GiB (94%)
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Audio
ID : 2068 (0x814)
Menu ID : 100 (0x64)
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 2
Codec ID : 3
Duration : 1h 2mn
Bit rate mode : Constant
Bit rate : 384 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Compression mode : Lossy
Delay relative to video : -181ms
Stream size : 172 MiB (2%)

Menu
ID : 129 (0x81)
Menu ID : 100 (0x64)
List : 2064 (0x810) (MPEG Video) / 2068 (0x814) (MPEG Audio) / 2069 (0x815) () / 2065 (0x811) ()


M2TS
----

General
ID : 1 (0x1)
Complete name : C:\Video\Work\Camcorder\Tape 1.m2ts
Format : BDAV
Format/Info : Blu-ray Video
Commercial name : HDV 1080i
File size : 11.4 GiB
Duration : 1h 1mn
Overall bit rate mode : Variable
Overall bit rate : 26.6 Mbps
Maximum Overall bit rate : 35.5 Mbps

Video
ID : 4113 (0x1011)
Menu ID : 1 (0x1)
Format : MPEG Video
Commercial name : HDV 1080i
Format version : Version 2
Format profile : Main@High 1440
Format settings, BVOP : Yes
Format settings, Matrix : Custom
Format settings, GOP : M=3, N=15
Codec ID : 2
Duration : 1h 1mn
Bit rate : 25.0 Mbps
Width : 1 440 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate : 29.970 fps
Standard : Component
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Interlaced
Scan order : Top Field First
Compression mode : Lossy
Bits/(Pixel*Frame) : 0.536
Stream size : 10.7 GiB (94%)
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709

Audio
ID : 4352 (0x1100)
Menu ID : 1 (0x1)
Format : MPEG Audio
Format version : Version 1
Format profile : Layer 2
Codec ID : 4
Duration : 1h 1mn
Bit rate mode : Constant
Bit rate : 384 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Compression mode : Lossy
Delay relative to video : -296ms
Stream size : 168 MiB (1%)


MKV
---

General
Unique ID : 210217485311190726988062280093030469844 (0x9E266A3C180BD7D68F4E75AA1B58D0D4)
Complete name : C:\Video\Work\Camcorder\Tape 1.track_4113.mkv
Format : Matroska
Format version : Version 4 / Version 2
File size : 9.15 GiB
Duration : 1h 0mn
Overall bit rate : 21.5 Mbps
Movie name : Tape 1
Encoded date : UTC 2013-09-18 23:34:56
Writing application : mkvmerge v6.4.1 ('Omega Point') built on Sep 16 2013 22:05:10
Writing library : libebml v1.3.0 + libmatroska v1.4.1

Video
ID : 1
Format : MPEG Video
Commercial name : HDV 1080i
Format version : Version 2
Format profile : Main@High 1440
Format settings, BVOP : No
Format settings, Matrix : Custom
Codec ID : V_MPEG2
Codec ID/Info : MPEG 1 or 2 Video
Duration : 1h 0mn
Bit rate : 20.7 Mbps
Maximum bit rate : 25.0 Mbps
Width : 1 440 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 29.970 fps
Standard : Component
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Interlaced
Scan order : Top Field First
Compression mode : Lossy
Bits/(Pixel*Frame) : 0.444
Time code of first frame : 00:00:00:00
Time code source : Group of pictures header
Stream size : 8.80 GiB (96%)
Title : Video
Language : English
Default : Yes
Forced : No
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 : 1h 0mn
Bit rate mode : Constant
Bit rate : 384 Kbps
Channel(s) : 2 channels
Sampling rate : 48.0 KHz
Compression mode : Lossy
Delay relative to video : -67ms
Stream size : 167 MiB (2%)
Title : Audio
Language : English
Default : Yes
Forced : No



Thanks for any guidance!


Damon

P.S. Apologies if this is a re-post. I tried to post once before but it never showed up.

 

It's probably that the muxer uses less overhead to get the streams into the mkv container.
I record .wtv (in my case mpeg2 files) and demux/remux them to .mpg and the file size gets larger - but there's no re-encoding taking place.

 

I have an even more dramatic example, converting a format BDAV to format Matroska:

$avconv -i input.m2ts -vcodec libx264 -acodec libvorbis output.mkv

$ls -l input.m2ts
-rw------- 1 patel patel 21963687936 ...

$ls -l output.mkv
-rw------- 1 patel patel 1863399876 ...

The new file is less than 8.5% of the size of the original! There are fewer audio and subtitle streams, but surely that couldn't account for much. The resolution of the video seems to be the same.

input.m2ts:

output.mkv:

I can't perceive a difference when viewing the original versus the copy. Can someone explain what information is being stored in the m2ts file that uses an extra 18.7 GiB but to all appearances is imperceptible?

 

Start a new topic as per forum rules regarding hijacking threads
also before replying to any topic check the last reply date,this thread is getting onto 3 years old