how/where you can join clips with Streamclip
It was explained in the link in my previous post in this thread... Also MPEG Streamclip guide explains it.
MPEG Streamclip can join similar MPEG files: The joined files must have the same PIDs, the same start codes, and the same audio/video properties (that is, they must come from the same source or channel).
Using "Convert to MPEG" before joining the files can be helpful, because it changes PIDs and start codes to a default value. The preferred method to join streams is to Copy one stream in MPEG Streamclip, open another stream and Paste it there. This method checks that the joined streams indeed are compatible. Another method is to put the MPEGs in the same folder, and rename them so that they sort as desired in list view. Then select them via MPEG Streamclip's "File/Open Files..." dialog box (Shift- or Command-click to select multiple MPEGs). Then choose "Edit/Fix Timecode Breaks". After this MPEG Streamclip should report the combined length of all MPEGs (check the Log Window if you want to know whether any timecode breaks were found). Then choose "File/Convert to MPEG... or /Save As..." to save them in a single file. If the video transition between two files looks bad, you can use the Cut command to improve it. You can join very different and incompatible MPEGs with this latter method so the end result is not guaranteed to work.
MPEG Streamclip can also edit MPEG files. Just set In/Out points (with I/O keys), Cut unwanted material off and choose "File/Convert to MPEG...". You can also Cut/Copy selections to other parts of the same stream or open another compatible stream and Paste it there. Shift-dragging the playhead can also be used to define a selection. Option + arrow keys jump to the beginning/end or In/Out points. You can use the Trim-command to more closely see a part of the video before cutting, then choose Revert Trimming to see all material. JKL-keys can be used to enable fast forward or reverse playing. The scroll wheel works also; with the Option key it scrolls 1 second per click. See the manual for more details on how to jump in single frame, GOP, 1 second, 10 second or 1 minute chunks when searching a specific spot in the video.
Editing and trimming can be accurate only if In and Out are both on keyframes because MPEG Streamclip edits to the GOP, not to the frame. For DVD and (XS)VCD the maximum GOP size is PAL 15 and NTSC 18 frames, so the editing accuracy can be up to about 0.6 seconds. You can advance to the previous or next keyframe (i.e. I-frame, the beginning of each GOP or Group Of Pictures) with the Up/Down arrow keys -- you can also use the Edit/Go to Keyframe command to see where the In and Out points really are when editing (the In point is included in the selection, the Out point is not included). Shift + Up/Down arrow keys allow fine-tuning the selection to the GOP.
