mkvmerge Videosize/Bitrate change after merge?

[ck0]

Hello everbody,

i used mkvmerge to remove audio lines from mkvs. I recognized that after the audioline has been removed the videosize & bitrate changed. Can anyone explain this to me? Thanks in advance!!

Here is some MediaInfo output:

Original:

General
Complete name                    : M:\original.mkv
Format                           : Matroska
File size                        : 5.70 GiB
Duration                         : 1h 57mn
Overall bit rate                 : 6 939 Kbps
Encoded date                     : UTC 2010-05-18 08:31:21
Writing application              : mkvmerge v3.0.0 ('Hang up your Hang-Ups') built on Dec 12 2009 15:20:35
Writing library                  : libebml v0.7.9 + libmatroska v0.8.1
 
Video
ID                               : 1
Format                           : AVC
Format/Info                      : Advanced Video Codec
Format profile                   : High@L3.1
Format settings, CABAC           : Yes
Format settings, ReFrames        : 2 frames
Muxing mode                      : Container profile=Unknown@3.1
Codec ID                         : V_MPEG4/ISO/AVC
Duration                         : 1h 57mn
Bit rate                         : 3 781 Kbps
Width                            : 1 280 pixels
Height                           : 528 pixels
Display aspect ratio             : 2.40:1
Frame rate                       : 23.976 fps
Color space                      : YUV
Chroma subsampling               : 4:2:0
Bit depth                        : 8 bits
Scan type                        : Progressive
Bits/(Pixel*Frame)               : 0.233
Stream size                      : 3.10 GiB (54%)
Writing library                  : x264 core 80 r1376 3feaec2
Encoding settings                : cabac=1 / ref=2 / deblock=1:-1:-1 / analyse=0x3:0x113 / me=hex / subme=6 / psy=1 / psy_rd=1.0:0.2 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-3 / threads=6 / sliced_threads=0 / nr=0 / decimate=1 / mbaff=0 / constrained_intra=0 / bframes=4 / b_pyramid=0 / b_adapt=2 / b_bias=0 / direct=1 / wpredb=1 / wpredp=2 / keyint=250 / keyint_min=25 / scenecut=40 / rc_lookahead=30 / rc=crf / mbtree=1 / crf=18.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
 
Audio #1
ID                               : 2
Format                           : DTS
Format/Info                      : Digital Theater Systems
Codec ID                         : A_DTS
Duration                         : 1h 57mn
Bit rate mode                    : Constant
Bit rate                         : 1 510 Kbps
Channel(s)                       : 6 channels
Channel positions                : Front: L C R, Side: L R, LFE
Sampling rate                    : 48.0 KHz
Bit depth                        : 24 bits
Stream size                      : 1.24 GiB (22%)
Title                            : German
Language                         : German
 
Audio #2
ID                               : 3
Format                           : DTS
Format/Info                      : Digital Theater Systems
Codec ID                         : A_DTS
Duration                         : 1h 57mn
Bit rate mode                    : Constant
Bit rate                         : 1 510 Kbps
Channel(s)                       : 6 channels
Channel positions                : Front: L C R, Side: L R, LFE
Sampling rate                    : 48.0 KHz
Bit depth                        : 24 bits
Stream size                      : 1.24 GiB (22%)
Title                            : English
Language                         : English

After the use of mkvmerge:

General
Complete name                    : M:\merge.mkv
Format                           : Matroska
File size                        : 4.45 GiB
Duration                         : 1h 57mn
Overall bit rate                 : 5 426 Kbps
Encoded date                     : UTC 2010-09-05 19:58:00
Writing application              : mkvmerge v4.3.0 ('Escape from the Island') gebaut am Sep  5 2010 10:30:51
Writing library                  : libebml v1.0.0 + libmatroska v1.0.0
 
Video
ID                               : 1
Format                           : AVC
Format/Info                      : Advanced Video Codec
Format profile                   : High@L3.1
Format settings, CABAC           : Yes
Format settings, ReFrames        : 2 frames
Muxing mode                      : Container profile=Unknown@3.1
Codec ID                         : V_MPEG4/ISO/AVC
Duration                         : 1h 57mn
Bit rate                         : 3 808 Kbps
Width                            : 1 280 pixels
Height                           : 528 pixels
Display aspect ratio             : 2.40:1
Frame rate                       : 23.976 fps
Color space                      : YUV
Chroma subsampling               : 4:2:0
Bit depth                        : 8 bits
Scan type                        : Progressive
Bits/(Pixel*Frame)               : 0.235
Stream size                      : 3.13 GiB (70%)
Writing library                  : x264 core 80 r1376 3feaec2
Encoding settings                : cabac=1 / ref=2 / deblock=1:-1:-1 / analyse=0x3:0x113 / me=hex / subme=6 / psy=1 / psy_rd=1.0:0.2 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-3 / threads=6 / sliced_threads=0 / nr=0 / decimate=1 / mbaff=0 / constrained_intra=0 / bframes=4 / b_pyramid=0 / b_adapt=2 / b_bias=0 / direct=1 / wpredb=1 / wpredp=2 / keyint=250 / keyint_min=25 / scenecut=40 / rc_lookahead=30 / rc=crf / mbtree=1 / crf=18.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
 
Audio
ID                               : 2
Format                           : DTS
Format/Info                      : Digital Theater Systems
Codec ID                         : A_DTS
Duration                         : 1h 57mn
Bit rate mode                    : Constant
Bit rate                         : 1 510 Kbps
Channel(s)                       : 6 channels
Channel positions                : Front: L C R, Side: L R, LFE
Sampling rate                    : 48.0 KHz
Bit depth                        : 24 bits
Stream size                      : 1.24 GiB (28%)
Title                            : German
Language                         : German

[jagabo]

I believe MediaInfo estimates the video bitrate based upon the size of the file, the size of the audio tracks, etc. It doesn't fully take into account all the overhead. It's not surprising that removing a large audio track would effect that calculation. The video track itself did not change.

[ck0]

The video track itself did not change.

Thanks for your reply. Do you know a tool to verify this? Or a tool that works more accurate as MediaInfo?

[poisondeathray]

Mkvmerge cannot alter the elementary video stream (it doesn't re-encode, and has no capacity to do so)

You can use mkvextract to extract the elementary video stream from both videos and check them. You can look at the filesize and/or use bitrate viewer on the elementary video stream to see the distribution ; or even better, elecard streameye which is more accurate , but not free (bitrate viewer only samples a few frames, streameye looks at every frame)

If you are paranoid, you can also use a md5 checksum tool (e.g. little md5 creator) .

[jagabo]

Windows' command line file comparison tool: FC (file compare), use the /b switch for binary files:

FC /b file1 file2

This performs a byte for byte comparison so you have to demux the video streams first (otherwise the differing audio streams would cause the comparison to fail).

[ck0]

Okay.. Thank you very much to everyone. I will try to extract both video streams and compare them

[jagabo]

Of course, if you were really paranoid, you might be afraid that the act of extracting the video from the original file caused the same damage as removing one audio stream!

You could further try muxing the removed audio stream back into the file without it. Then compare what MediaInfo says about the original file and the new file with both audio streams. But you should also be aware that different programs can multiplex differently*. So even that may not show the exact same bitrate. To accurately determine the bitrate a program has to read through the entire video and examine every frame. That takes time and knowledge of the data structures within the file so few programs do it. GSpot can do it for AVI file.

* For example, one program may save a 25 fps video as one frame of video then 1/25 second of audio, repeating that over and over. Another might save two frames of video followed by 2/25 seconds of audio, repeating that pattern. The files would be slightly different sizes because each "chunk" of data has a small header that indicates what that chunk is and how big it is. So if the first file has 1000 frames of video it also has 1000 chunks of audio. The second file has 1000 frames of video but only 500 chunks of audio -- its size will be a little smaller.