Q: ffmpeg syntax for VC1 to H.264?

[DanielCoffey]

I have just started using MP4Tools on my Mac Mini to convert some MKV BDs to M4V for watching on an Apple TV 4 and while it is great for remuxing from MKV to M4V, I am finding the Mac Mini struggles when transcoding a video stream from VC1 to H.264.

I would like to deal with the VC1 to H.264 transcodes on my main machine (i7 4770K 4.5GHz) using ffmpeg because it will finish much faster. I don't have a great many to do but the Mac Mini takes around 9 hours to complete one on its i5 2.6GHz processor.

Given the following MP4Tools settings, what would you suggest as the ffmpeg command line for both the video and audio?



I would like to preserve the full quality if at all possible as I like the final result and the file size is comparable to the original MKV. I do have some that are vc1, ac3 5.1 already so for those the audio would be copied. This one has an audio conversion too.

On a separate question, is there a forum to report bugs in the MP4Tools program? I have found one MKV that crashes it on startup and another that crashes it on exit. I assume it might be the VideoHelp - Mac subforum?

[pandy]

https://trac.ffmpeg.org/wiki/Encode/H.264#twopass

ffmpeg -y -i input -c:v libx264 -preset medium -b:v 15000k -pass 1 -c:a ac3 -b:a 448k -f mp4 /dev/null && \
ffmpeg -i input -c:v libx264 -preset medium -b:v 15000k -pass 2 -c:a ac3 -b:a 448k output.mp4

Or better

ffmpeg -y -i input -c:v libx264 -preset medium -crf 17 -pass 1 -c:a ac3 -b:a 448k -f mp4 /dev/null && \
ffmpeg -i input -c:v libx264 -preset medium -crf 17 -pass 2 -c:a ac3 -b:a 448k output.mp4

[DanielCoffey]

That's the bunny, thanks!

At the moment I am trying your first example of matching the bitrate to what was in the original vc1 stream and it is running much faster on my main machine. It looks like the two passes will be finished in around 1h30 compared to the 9 hours on the Mac mini.

I will then run the second example on the same file and see how the file size and bitrate compare. I have no shortage of storage space so we are hoping to keep the movies as close to the original MKV as possible.

I really appreciate the help.

EDIT : Pass 1 completed in exactly 30 minutes (averaging at 3.3x speed) since it was reading only but pass 2 seems to be going at about 1.2x so far so I think somewhere around 2h00 is about right. CPU temps are much better on this machine too since it is water cooled. Only 7C over ambient for pass 1 and 8C over ambient for pass 2. I really felt that the Mac Mini was struggling and was rather warm to touch.