Ability to set start position for audio and video elements

See: https://discuss.streamlit.io/t/feature-request-provide-start-position-for-playback-in-the-audio-player/343

Proposed API:

st.audio(data, format="audio/wav", start_time=0)
st.video(data, format="video/mp4", start_time=0)

The reason start_time goes at the end is because it’s less likely people will want to set that arg than the format arg.

There was also some discussion about calling it “current_time” vs. “start_time”, but we decided on the latter because “current_time” just sounds confusing in this context. Sure we’re using the HTML currentTime property under the hood —but while that name makes sense as a dynamic property you can read/write in JS, it does not make sense as a static property that you only set once.

API status: ready to implement

The MDN entry for <audio> element shows you can easily do this by setting the currentTime attribute.

[mrunderline]

I read updated issue body and your new comment on the PR. While developing, I was thinking like you, but the issue body was different so I respect it. But finally it’s OK and I’ll do them.

[nthmost]

Merged into develop, so closing as complete. Thanks @mrunderline !