simple arguments that dont make MP4 with youtube-dl.exe that used to work

[sommers]

SET W1=https://www.youtube.com/watch?v=870y6GUKbwc&nohtml5=False
SET P1=C:\youtube-dl.exe
---------------------------------------------------
AA=
SET Z1="C:\ffmpeg 64bit\ffmpeg.exe"

SET F1=--write-auto-sub
SET F2=--sub-lang en
SET F3=--sub-lang de
SET F4=--convert-subs srt
SET F5=--ffmpeg-location %Z1%

M:
CD M:\
START %P1% %F1% %F2% %F3% %F4% %F5% %W1%
-------------------------------------------------------
BB=

M:
CD M:\
START %P1% %W1%
-------------------------------------------------------

BB=works and makes MP4
AA=works but doesnt make MP4 and it makes MKV instead, and it says there is an error that cant make MP4, it used to work and make MP4 long ago,

MKV is not good for XP, and i need MP4, because of this, i have to download 2 times AA= way and BB= way.
what is wrong with AA=?

[jagabo]

You can't put SRT subs in an MP4 file.

[sneaker]

Try:

SET W1=https://www.youtube.com/watch?v=870y6GUKbwc&nohtml5=False
SET P1=C:\youtube-dl.exe
---------------------------------------------------
AA=
SET Z1="C:\ffmpeg 64bit\ffmpeg.exe"

SET F1=--write-auto-sub
SET F2=--sub-lang en
SET F3=--sub-lang de
SET F4=--convert-subs srt
SET F5=--ffmpeg-location %Z1%
SET F6=-f "bestvideo[vcodec^=avc1][height<=1080]+bestaudio[acodec^=mp4a]/best[vcodec^=avc1][height<=1080]"

 M:
 CD M:\
 START %P1% %F1% %F2% %F3% %F4% %F5% %F6% %W1%
 -------------------------------------------------------
BB=

M:
CD M:\
START %P1% %W1%

https://github.com/ytdl-org/youtube-dl/blob/master/README.md#format-selection

[sommers]

SET F6=-f "bestvideo[vcodec^=avc1][height<=1080]+bestaudio[acodec^=mp4a]/best[vcodec^=avc1][height<=1080]"
thanks, this will do although i have no idea why it looks so difficult.
but
mp4 created by BB= with %F6% is different from the mp4 created by AA=.
so far,
the sizes are slightly different
i can not tell the quality differences yet, because i havent downloaded enough, i havent checked enough with %F6%

[sneaker]

Youtube offers many different formats to cater to all kind of different devices and from time to time adds newer, more efficient codecs. The default selection for your video is currently AVC-in-mp4 video and Opus-in-WebM audio. Youtube-dl combines those into MKV container by default instead of MP4. My command forces to download AVC video and AAC audio (in mp4/m4a container) which is compatibly with more devices and which Youtube-dl puts into mp4 container by default. (I also set max video height to 1080 pixels since you seem to be using an old computer.)

So the size is slightly different because the audio format and container format are different. The video track is exactly the same as before.