re-encoding in copy mode?

[terminaltrip421]

I'm using 2.7.2
as is likely evident by my question to say my knowledge is limited would be an understatement.
I'm making clips using copy mode and .mp4 muxer from a video encoded using CBR and the copied videos are coming out with varying bitrates. while I'm inclined to assume that that's because the bitrates in the original do vary despite the 'constant' designation; when saving the file I'm also getting "encoding file..." rather that "saving..." or "copying..." I'm wondering there is reencoding going on.

[eumagga0x2a]

I'm using 2.7.2

This is an unsupported obsolete version, please update preferably to the latest 2.8.2 nightly, skipping the 2.8.1 release.

when saving the file I'm also getting "encoding file..." rather that "saving..." or "copying..." I'm wondering there is reencoding going on.

The dialog, opened by muxer, really doesn't know anything about the source of the compressed packets the muxer receives. If the selected codec is "Copy", it will be copy.

However, there is one detail, relevant to your question. If the source video is a MPEG-TS file, constant bitrate of the stream may have been achieved not by the encoder but by the muxer injecting padding NAL units into the AnnexB type of H.264 or HEVC stream. Avidemux discards such ballast when converting stream from AnnexB to ISO (MP4), resulting in the bitrate of the video stream becoming variable.

[terminaltrip421]

thank you very much!

I had actually upgraded and went back to 2.7.2 because I had the same fear with a different file where the file was taking so long that I though for sure it had to be reencoding though in that instance I thought it was likely due to the audio source having only just gained support.

[eumagga0x2a]

If the application doesn't behave as expected, a look into the log (Help --> Advanced --> Open Application Log) may give some clues.

I had the same fear with a different file where the file was taking so long that I though for sure it had to be reencoding

When outputting a MP4 file with optimization for streaming enabled, the last step of rewriting the entire file in order to move the index from the end of the file to the head, may take a lot of time depending on mass storage performance.

[terminaltrip421]

thanks.  I do have tendency to run my HDD to empty and I might have even been using an external drive. it occurs to me that it my have been an ultra high resolution file too. 

[terminaltrip421]

sorry to revive the topic ... I installed the newest nightly and made comparisons because I can't help myself and was wondering if it would be possible to explain why the outputted files' video info might differ using copy for both. using the 2.7.2 I get a flat 15.0 Mbp and with both 2.8.1 (already had it downloaded) and 2.8.2 I get a range of 14.3 and 14.9 max (it's nice they both are consistent at least) and a larger file size for the 2.7.2 files @ 82.1 MB vs 81.8 for the 2.8 versions.