make cache mechanism work like the firefox's video playback cache

[rezad1393]

In mpv forward cache works like this:
mpv reads 400MiB (user set amount) of data from disk to RAM so that user can seek forward (and backward) fast in the playback stream and don't wait for data fetch from storage drive (for example slow HDD).

and when user watches the video the app always fetch more of data from drive.
this causes the storage drive to always be engaged.
or put another way the buffer is a constant length from playing frame to the last cached byte )

In firefox video playback buffer (cache) works a bit differently.
it has the the buffer length like mpv called media.cache_readahead_limit but it also has a threshold that needs to be reached when going through buffer for firefox to fetch more data called media.cache_resume_threshold . (they are set by seconds not size (MiB)).

Equivalent of this for mpv would be that if a user opened a 2GiB video file and set these two setting to 400MiB and 100MiB then at first the mpv would read and cache 400MiB and then when user watches the video it does not continuously fetch more data until the cache buffer has gotten to the last 100MiB of 400MiB and then mpv reads and caches another 300MiB and so on.

I believe this is a better way to implement cache system.

this way user can use cache a way to make HDD less used and less noisy and let HDD goes to sleep (drive spin-down) more.
even SSD are better utilized this way.

[guidocella]

--demuxer-hysteresis-secs=10

[rezad1393]

is that the threshold one?
I searched the config man for the word threshold but didn't find that.

is there a setting for bytes instead of seconds?

[kasper93]

Please read the documentation. Caching in mpv is very flexible, and you can do all that you describe in your post, and more.

[rezad1393]

Ok, in this case byte based hysteresis is not supported. We may add it, should be trivial change.

that is exactly what I want because seconds doesn't exactly translate to file size, so I cant manage or predict neither my RAM usage based on video files opened simultaneously (which can fill my ram and make issues for other apps) nor my HDD load activity based on calculating what is a good amount of data to get between drive rests.

As my os and home are on SSD but my big data (movies) are on external HDD drive, I prefer for that drive to not always be spinning.

[kasper93]

Added in #17890

[Jules-A]

Added in #17890

Thanks, I was actually after that for years.

Do you know if it would be viable to reduce IO priority when buffer reaches a certain point?
I have a slight issue when my CPU is under heavy load combined with decent amount of IO such as MPVs caching, it can cause audio to pop/crackle. The new option may help but it will still cache at normal priority when it goes under that amount.

[kasper93]

You mean thread priority? I think we already should have audio threads set to high priority, not sure if we can improve there.

[Jules-A]

You mean thread priority? I think we already should have audio threads set to high priority, not sure if we can improve there.

I thought there was another way, https://learn.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-file_io_priority_hint_info maybe? At least on Windows, I'm not even sure if it's an issue on Linux.