Why do these two videos load so differently?

[Trevor10]

The MediaInfo for the first video is attached.
The MediaInfo for the second video is attached.

A capture that I made showing the videos loading can be found at https://www.dropbox.com/s/qfbnu3sjjceirg7/Avidemux_Loading.mp4?dl=0. Login to Dropbox to download the original 1440p file for best quality.

Also, when I play either video in Avidemux, the playback is slow and the audio desyncs. Both videos playback fine on MPC-HC.

Thank you.

[eumagga0x2a]

In the Matroska demuxer we parse the whole H.264 stream decoding type (keyframe, P-frame, B-frame) of every frame. This takes a lot of time and effort. In the MP4 demuxer, we don't do that, we just take the info from the container which frames are keyframes and call all other frames P-frames (which is the default). The video decoder identifies the frame type to be shown in the GUI later.

You should try enabling DXVA2 hardware accelerated decoding in Avidemux' Preferences. While it might be still not enough to enable playback in real time for 4K, it should massively improve the situation anyway.

We don't yet support full HW accel on Windows, i.e. we have to download the decoded video from the graphics card to the main memory and subsequently reupload it to the graphics card for display. Your MPC-HC is probably doing everything in the graphics card, avoiding wasteful copying of huge amounts of data back and forth.

[Trevor10]

Thank you for the reply. I'll stick to mp4 files. I enabled DXVA2 and it helped a lot. Audio is in sync and video is playing much faster. When I checked this post while not logged-in, I couldn't see the attached txt files. Are they being hidden for some reason?

[eumagga0x2a]

Yes, attachments are hidden for guests (I don't know exactly why, it is just this way).

If you stick to mp4 files, it makes a lot of sense to use the latest nightly.

[Trevor10]

Thanks again. Yes, I am using the latest nightly: avidemux_2.7.5 r200123_win64.exe. Is mkv better than mp4 for Avidemux?

One other thing that I'm wondering is why the parsing isn't faster. As you can see in the video, neither the SSDs nor any of the CPU cores are even close to max, so there seems be unused performance. Is there a way to get Avidemux to fully use my hardware?

[eumagga0x2a]

Yes, I am using the latest nightly: avidemux_2.7.5 r200123_win64.exe.

Good.

Is mkv better than mp4 for Avidemux?

No. For now, mp4 is maybe somewhat better because both the demuxer and muxer have been modified to properly handle time base and frame rate. The matroska demuxer and the MKV muxer still require work on this topic.

One other thing that I'm wondering is why the parsing isn't faster. As you can see in the video, neither the SSDs nor any of the CPU cores are even close to max, so there seems be unused performance. Is there a way to get Avidemux to fully use my hardware?

Parsing is single-threaded, so it appears on average as 1/16 of 100%  = 6¼% per core.