Rducing file size with 4K video -> IQ problem

[BG Davis]

 
I like to shoot short (less than one minute) sports video clips at 60p, then slow them down to 24fps for a slow motion effect and save as Mpeg4 AVC (x264).  I then send them by email to the subjects.  To avoid clogging up my email and those of the recipients, I use Avidemux to configure them to 15-20mb (depending on length).
When I shoot AVCHD, this is not a problem; the IQ is very good.  Hardly distinguishable from the original.
When I got a Lumix G9, I started shooting 4K60p (MP4). I would then slow them down to 24fps and configure to 15-20mb as before.
The problem: the 4K>15-20mb clips have terrible IQ.  There is a lot of flickering and blocking of small groups of pixels.
I tried adding one step to the process: downsize to 1080p before configuring to 15-20mb.  This didn't help.  IQ is still awful.
Has anyone else had this problem?  Is there a solution?

[eumagga0x2a]

1) Please don't abuse email to send anything > 1 MB in size, use a service like Dropbox.

2) Please show the complete project script for a 4k clip. You may edit it to remove the path to the source video. 20 MB equals just a couple of seconds worth of 1080p@24fps video at a decent quality level.

[BG Davis]

"Please don't abuse email to send anything > 1 MB in size, use a service like Dropbox."
Not really necessary or desirable for communication.  Most people I know don't even know what Dropbox is and they don't want to fool with extra stuff.

"Please show the complete project script for a 4k clip."
How do I do that?  The only options I see are "Save as" and "Run" but nothing to actually see and copy the script.  Do I just append the py file?

"20 MB equals just a couple of seconds worth of 1080p@24fps video at a decent quality level."
I beg to differ.  Unfortunately I can't attach a clip to prove my point.  On clips of 30 seconds or so, at 15-20mb most people would not notice any difference from the original.  In fact, I've had people ask what camera I used to get such nice video.  For email, I'm not concerned with big-screen TV footage; the stuff I send looks very nice on a 17" monitor at full screen, which is larger than most people are going to view it at.  For original quality, I'll give them a USB drive.

[eumagga0x2a]

Please don't abuse email to send anything > 1 MB in size, use a service like Dropbox.

Not really necessary or desirable for communication.  Most people I know don't even know what Dropbox is and they don't want to fool with extra stuff.

It is not much more than clicking a link in a browser. The fact that people are used to do something in a particular way doesn't make this way automatically right. base64 algorithm used to encode binary attachments as plain text additionally inflates their size by 1/3. Many email providers impose intransparent storage space and message size limits, a few gigantic emails can easily consume this space with severe impact on users.

(I just had to sort out such a case: zero notifications for the affected user, no bounces, unknown number of important messages lost, the provider was silently dopping all arriving messages until I freed space deleting a couple of emails with big attachments.)

Please show the complete project script for a 4k clip.

How do I do that?  The only options I see are "Save as" and "Run" but nothing to actually see and copy the script.  Do I just append the py file?

A "py file" is simply a text file with .py extension, open and edit it with any text editor supporting Unix-type line breaks (the LF character alone instead of the CR LF sequence). Even notepad.exe supports this on the last iteration of Windows 10 (but not on Windows 7). Finally, paste the content into the body of your reply.