OT: A few ffmpeg queries

[Alan Milewczyk]

This is OT, so if you're offended, apologies and please ignore this e-mail!

Looking for some ffmpeg advice and comments please.

I have a Freesat box, a Humax Foxsat-HDR, which records TV programmes in 
.ts format. Each video programme also has a couple of support files:

.nts files which contain the timing information required to provide 
seeking, and play from last position functions on the HDR and

.hmt files which contain full details of the recording, including EPG 
information

My understanding is that the video stream is mp2 (MPEG-2). The audio is 
usually just the one stream, but sometimes two streams (a standard and a 
narrated (NAR) stream).

I've been remuxing these recordings into MP4 format for eventual 
transfer onto my NAS. I also use the AV2HDR program which reads the EPG 
info so I can tag the mp4 files manually.

I've noticed that the remux process takes significantly longer than the 
same process in get_iPlayer. To give an example, with giP, a one hour 
programme takes less than half a minute to remux to mp4 on my PC whereas 
it's rarely faster than 2x, indeed usually less than 1.0x, so films can 
take some time.

I'm using a copy of the same version of ffmpeg used in gip but in its 
own separate remux folder. The relevant  command used is:

             ffmpeg -i progname.ts -c:av copy progname.mp4

My understanding is that this should copy over the audio and video 
streams unaltered but in an mp4 container. However, this does not appear 
to be the case - not only does this process take significantly longer 
than the gip equivalent but it's a heck of a resources hog, typically 
90%+ CPU usage (negligible in gip). In addition the file sizes are 
smaller with lower bitrates, so it would appear to be re-encoding in the 
process. I like ffmpeg because I can top and tail my recordings by 
specifying start and end times (to cut out extraneous content) while 
doing the remuxing, but as it stands the remuxing time is frustrating, 
to say the least, not to mention the other issues highlighted in this 
e-mail.

Just wondering whether anyone can shed some light on these 
discrepancies, please.

Thanks


Alan



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