[Reuben Martin]

Yes, ffmpeg support quite a few pixel formats that include an alpha channel. You have to specify the pix_fmt, and obviously your source has to have an alpha channel.

[Reuben Martin]

This doesn’t make much sense. Are you perhaps confusing multiple audio streams with a single audio stream that has multiple channels?

[Reuben Martin]

You can encode data into additional video, audio, or subtitle streams. LTC for example is simply an audio track with time code data modulated as an audio signal.

So yes you can, but you have to have something to take the data and decode / act upon the data at the receiving end. Encoding commands into a subtitle stream would probably be easiest if it’s something like text based commands. Analog signaling would best be modulated into and audio or video stream.

[Reuben Martin]

Yes, as long as the browser supports the draft HTML5 File API.

https://www.html5rocks.com/en/tutorials/file/dndfiles/

[Reuben Martin]

No, most big website offer multiple sources tags within a video tag for different browsers and platforms.

Firefox and Opera for instance will not play mp4 files and only accepts webm and ogg. (Well, until today at least. Firefox 33 released just today now natively supports mp4, thanks to cisco.) Internet Explorer and Safari only support mp4. Chrome has supported all 3 for quite a while.

Mobile devices are even more fragmented. Many devices only support baseline profile, (which kinda sucks) though the newer ones are starting to support main and high profiles. Very few of them have acceleration for decoding webm or ogg. And even then it’s highly recommended to use something like HLS that serves the video in chunked format so that it doesn’t waste mobile bandwidth.

So, if you want a “single encode” that has the most broad support you can try the following:

ffmpeg -i <input_file> -c:v libx264 -crf 20 -g 45 -profile:v baseline -pix_fmt yuv420p -c:a libfdk_aac -vbr 3 -f mp4 -movflags faststart <output_file>

[Reuben Martin]

Doesn’t really make any difference. The only real tool you have on a client browser. And the JS environment is sandboxed from the file system. You cannot access files without a lot of user interaction. And even then there is no direct javascript API by which to extract individual frames from a video stream.

The only thing you could do is have a video element paint it’s output to a canvas element, and the bitscrape the image off the canvas. https://appcropolis.com/blog/web-technology/using-html5-canvas-to-capture-frames-from-a-video/

[Reuben Martin]

Not possible. And least not in the practical sense.

The client end either needs to have a web server to host the stream, or an RTMP server to push the stream, or the content producer needs to output the file in chunked format with the chunks being uploaded over a file transport of some kind.

[Reuben Martin]

PNG isn’t limited to 8bit.

[Reuben Martin]

There is no magic setting that works everywhere.

Different browsers support different combinations of codecs and formats. And even then sometimes a single browser offers different support for different platforms. Mobile devices support different encoding profiles depending on what chip they use to proved hardware accelerated decoding.

[Reuben Martin]

I don’t think those flags entirely do what their names would imply. I’ve run into timestamp issues multiple times and those flags have done little to fix the problem. A quick web search will reveal mailing lists littered with problems related to FFmpeg and DTS / PTS timestamp issues.