*.apkg

The .apkg file is a zip file (as you know). Inside, you'll find the collection (an sqlite3 database of notes/cards), the media file which you were trying to open, and a bunch of numbered files 0-whatever number(these are media files).

Just use 7zip tool open the apkg file and extract into a folder.
open the "media" file via a text editor tool to find the media file extension.

example of "media"

{"16486": "COCA_16486.mp3", }

rename "16486" file to a mp3 file, then you got the media file.

how media used in flash card

Export your flash cards into a plain text.

[sound:COCA_16486.mp3]

spatially	<div style=''>英['speɪʃəlɪ]  美['speɪʃəlɪ]</div>	<div style=''>adv.空间地，存在于空间地；</div>	"<div><br /></div><div style='color:RosyBrown'>ADJ</div><div style='color:OrangeRed'>空间的;与空间有关的</div><div style=""font-weight:bold;"">Spatial is used to describe things relating to areas.</div><div style=''><b>例：</b>...the spatial distribution of black employment and population in South Africa.南非黑人就业与人口的空间分布</div><div style=''><b>例：</b>...spatial constraints.空间的限制</div><div><br /></div><div style='color:RosyBrown'>ADJ</div><div style='color:OrangeRed'>(能力)理解立体空间的</div><div style=""font-weight:bold;"">Your spatial ability is your ability to see and understand the relationships between shapes, spaces, and areas.</div><div style=''><b>例：</b>His manual dexterity and fine spatial skills were wasted on routine tasks.他灵巧的动手能力和杰出的空间识别能力都浪费在日常事务上了。</div><div style=''><b>例：</b>...spatial awareness.空间方位感</div>"	<div style='color:DarkOrange; font-style:italic;'>adj:spatial; </div>		[sound:COCA_16486.mp3]	

example of web flash card

spatially

"<div style=""font-weight:bold;"">Spatial is used to describe things relating to areas.