How to edit VRO and REC files and use the MBS Scanner?

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2. How to edit VRO and REC files and use the MBS Scanner?

Most DVD recorders use a very limited file system when recording video, and they artificially combine multiple MPEG bit streams into one continuous file. Usually with a file name extension of ".VRO", ".REC", or ".VOB", those DVD recorder files contain multiple video segments each of which may use very different MPEG video and audio encoders. A DVD recorder can read this file by the help of an additional index file generated by itself; but those index files are mostly proprietary and not known to an external software editor.

As a result, most MPEG editors will encounter great difficulty in loading and editing those files, some of which may even crash. If an MPEG editor can open those files successfully, rarely can it read the content correctly. In those case, the common symptoms are (a) the length of video is too short, much shorter than what its file size has indicated; (b) the video and audio are completely out-of-sync; and (c) no random seek can be performed correctly.

To resolve this problem, we have created a tool called MBS Scanner, which scans and then disassembles a DVD recorder file into a set of segments.

When a single MPEG file contains one of the three changes listed below, we refer it as a Multiple Bit Stream (MBS) MPEG file.

1. timebase change, such as a time code restart;

2. video encoder settings change, such as image size, frame rate, and bit rate; and

3. audio encoder settings change, such as sampling frequency, bit rate, and number of sound channels.

As defined in MPEG standards, an MPEG movie stream should have a continuous time code to assist a decoder to synchronize its video and audio presentations. Also, an MPEG movie stream should not change, in the middle of the stream, its video encoder settings, or its audio encoder settings.

When an MPEG file contains one or all of the changes listed above, the editor will not be able to handle it correctly.

Typical examples of such files are MPEG files created by a digital camcorder with an internal MPEG recorder.

For a digital camcorder, one common usage is to take a sequence of shots and stops. And between shots, the camera settings may be changed, such as switching from an "SP" mode to an "LP" mode, which is essentially changing the video resolution and bit rate. For some camcorder, it also restarts the time code after a stop.

When a single MPEG file contains those changes within the file, we refer it as a Multiple Bit Stream (MBS) MPEG file.

Since an MPEG editor cannot correctly decode the second or the following segments of the same MPEG file without some additional information, and since it's hard to design a flexible MPEG player that can dynamically switch MPEG codec, the next best solution and perhaps the simplest solution to this problem is to divide the file into multiple segments, and treat each segment as an individual MPEG file, but without physically creating such segment files. This is what this utility does.

By scanning the MPEG file for any restart of its timecode and any change of MPEG encoder settings, it creates a list of segment files each of which saves a starting file offset and an ending file offset.

The segment file can be recognized by the MPEG editor by its file name extension of ".mbs", and be loaded properly as one complete MPEG stream.

Common examples of MBS files are VRO (".vro") files, DVD-R/W (".rec") files created by a DVD-R/W video recorder, and even some standard DVD (".vob") files.

The following is an example of multi-segment MPEG file,

D:\DVD recorder\PBC_ch9.vro

which contains two segments of MPEG recorded with a 720x480 resolution for the first segment and a 352x480 resolution for the second segment.

Two ".mbs" files will be created by the scanning process, and listed below.

(1) D:\DVD recorder\PBC_ch9.vro_1.mbs
[MBSFile]
NumFile= 1
File= D:\DVD recorder\PBC_ch9.vro
Segment= 0 93235200

(2) D:\DVD recorder\PBC_ch9.vro_2.mbs
[MBSFile]
NumFile= 1
File= D:\DVD recorder\PBC_ch9.vro
Segment= 93235200 147796772

Please also read the sections on MBS file scan.

Combine Multiple Segment Files Into One Continuous Stream

Another usage of this MBS file format is to combine a set of MPEG files which are really segments of one continuous MPEG stream, but cut into small pieces in order to satisfy the limitation of a file system, for example.

One typical example is the set of VOB files for one DVD program, such as the following list.

VTS_01_1.vob
VTS_01_2.vob
VTS_01_3.vob
VTS_01_4.vob

The corresponding ".mbs" file for this example is the following.

[MBSFile]
NumFile= 4
File= D:\VIDEO_TS\VTS_01_1.vob
File= D:\VIDEO_TS\VTS_01_2.vob
File= D:\VIDEO_TS\VTS_01_3.vob
File= D:\VIDEO_TS\VTS_01_4.vob

This is the reverse of a multi-segment file as explained previously.

Again, the MPEG editor will load this ".mbs" file and treat it as one continuous MPEG stream.

Note:
A different solution to the VOB file example given above is to use the newly created DVD Reader, which also heavily dependent on the usage of the MBS file format.