More questions about VP9 and WebM

[xyzone]

Sorry if I'm making too many threads. It seems like people just add on to huge threads but rarely make new ones.

Anyway, I'm curious about a couple of things:

Embedded webvtt subtitles. ffmpeg can do this automatically, converting other types of subtitles in the input into webvtt in webm output. mkvtools can't seem to do this. I can't even mkvextract the subtitles. It says "not supported". As far as playback, I have only seem mpv capable of playing these subs. VLC and browsers don't show any subtitles. So what is the deal with embedded webvtt subs? Is there a point to embedding them, as far as playback capability goes? If this is part of the webm spec, how can browsers display them?

2nd question is about alpha transparency in vp9. Simply put, how is this done (particularly in ffmpeg)? I've been trying to use pngs to create such a video, but it's not working. And yes, I am using profile 1 or 3. I try to set pix_fmt to something which seems appropriate, such as yuva420p, but it's not accepted by the encoder. When I use what is supported, the video only shows black instead of transparency.

[Jamaika]

Sorry if I'm making too many threads. It seems like people just add on to huge threads but rarely make new ones.
You should ask Mosu. I don't have to know everything about Matroska and WebVTT.
Embedded webvtt subtitles. ffmpeg can do this automatically, converting other types of subtitles in the input into webvtt in webm output. mkvtools can't seem to do this. I can't even mkvextract the subtitles. It says "not supported". As far as playback, I have only seem mpv capable of playing these subs. VLC and browsers don't show any subtitles. So what is the deal with embedded webvtt subs? Is there a point to embedding them, as far as playback capability goes? If this is part of the webm spec, how can browsers display them?
Matroska isn't interested in obsolete subtitles VTT. As it is in a container that has copied. The primary container is a ASS.
http://i67.tinypic.com/2zxqmj9.png
The problem is that Matroska container is added to Windows 10 or Cyberlink, but adding a container ASS no longer.
MKVmerge isn't compatible with MP4Box (WebVTT).
Text
ID : 2
Format : wvtt
Codec ID : wvtt
Duration : ----
Bit rate mode : Variable
Bit rate : 3 bps
Stream size : ---- Bytes (0%)
Title : vtt@GPAC0.5.2-DEV-rev1039-g22ad2b0-master

Extract:
mkvextract.exe tracks "input.mkv" --raw -c UTF-8 2:"output.vtt"
2nd question is about alpha transparency in vp9. Simply put, how is this done (particularly in ffmpeg)? I've been trying to use pngs to create such a video, but it's not working. And yes, I am using profile 1 or 3. I try to set pix_fmt to something which seems appropriate, such as yuva420p, but it's not accepted by the encoder. When I use what is supported, the video only shows black instead of transparency.
There isn't such thing as yuva420 for Vp10 / VP9 / VP8 in WebP / Webm. The specification is only yv12 / i420 / i422 / i444 / i440.