mdhiggins
commented
6 months ago This is more of a general FFMPEG question and maybe not the appropriate place to be asking but I can give some general guidance
Without logs it will be hard to nail down a specific bottleneck but there's always going to be some kind of bottle neck
If you're remuxing everything and doing no transcoding then your HDD (or SSD) read/write speeds will be your main bottle neck
Metadata writing for MKVs does do a second pass and essentially writes the metadata with a full remux transcode as a second step so this can add some time since it essentially has to rewrap the streams in a fresh mkv container, but this is only limited by your drive read/write so should be relatively quick still, mp4's don't have this limitation since they are written by mutagen (though mp4s usually get processed by qtfaststart which also needs to rewrap the file so you come out even)
Transcoding is always where you lose the most speed
Video being the slowest even with hardware transcoding Software video transcoding depending on hardware can take hours Certain filters aren't supported by hardware transcoding so even when using hardware you can have a software layer that slows it down substantially
Then audio FFMPEG audio transcoders are pretty much all single threaded and do not benefit from hardware acceleration so it can take some time for larger sources but still should be measured in minutes not hours, an order of magnitude faster than video
Then subtitles which is almost negligible since its only text based subtitles which takes a few seconds at most
The other thing to consider is source material; Content length/duration and bitrate play a huge role. Higher bitrate means more data. This makes every part of the process take longer. Remuxing will take longer just due to bigger size. Transcoding can take longer for more complicated formats (more audio channels, higher fidelity formats, higher bitrate all make audio transcoding more complicated and time consuming). And higher quality transcoding comes at the cost of time.
You can watch the SMA logs to see if there's a particular spot that things are hanging but the times you are reporting don't seem excessive
I also use a ramdisk for most of my transcoding which speeds things up but you need quite a bit of ram for this approach, but this won't be huge gains over an ssd
justinglock40
Is there some things I can do to speed up a AAC and English only SRT creations?
Right now a 3GB 1080p H.264 takes about 3-3 1/2 mins to copy the video and ac3 track and create an AAC track and remove all subs except english and make SRT
On a 4K Remux, this process is happening in about 10-15 minutes.
Hardware is a i5-9600K and the processing happens on a NVME PCIE 4 Gen 4. Not true issue, just wondering if something I'm doing is slowing this process down?