How Video Works
howvideo.works
How Video Works
1–10 of 26 posts
Re: How Video Works
#2I wish I knew all this earlier this year, so I'd be writting different thing as my thesis
Great explaination tho.
Re: How Video Works
#3I really love all the work the Mux team is doing! They don't just throw APIs over the wall. They are putting in lots of effort to educate/empower developers. This is good stuff, and not just propietary knowledge to sell something.
Also check out the video-dev Slack[0] and demuxed. Pion WebRTC and WebRTC for the Curious was motivated by conversations I had with other developers in their Slack.
Re: How Video Works
#4One thing i'd love to see added here is a blurb about the importance of the location of the video metadata in the file. Specifically that you need to have the metadata at the start of the file rather than the end of the file (which is the default) for low-latency playback on web.
Explained: Freshly recorded MPEG (and almost all other container types) typically saves the header at the end of the file. This is the logical place to store header information after recording as you just append to the end of the file you've just written. It's the default.
Unfortunately having the header at the end of the file is terrible for web playback. A user must download the entire video before playback starts. You absolutely need to re-encode the video with FAST-Start set.
The header location is the number one mistake that i've seen a lot of website and developers make. If you find your website videos have a spinner that's seconds long before the video playback starts check the encoding. Specifically check that you've set fast start.
I've seen companies who have a perfectly reasonable static site behind a CDN spend a fortune hosting their videos with a third party to fix the latency issues they were seeing. The expensive third party was ultimately fixing the issue because they re-encoded the videos with fast start set. The reality is their existing solution backed by a CDN would also have worked if they encoded the videos correctly.
Re: How Video Works
#5I really love all the work the Mux team is doing! They don't just throw APIs over the wall. They are putting in lots of effort to educate/empower developers. This is good stuff, and not just propietary knowledge to sell something. Also check out the video-dev Slack[0] and demuxed. Pion WebRTC and WebRTC for the Curious was motivated by conversations I had with other developers in their Slack. [0] https://video-dev.he…
Thank you so much for the kind words! For what it's worth, we're mods of video-dev, but we don't see that as "our" Slack, it's run by a bunch of folks in the online video community. Demuxed is similar in that we're organizers, but we 100% avoid it being a company conference.
Also, WebRTC for the Curious was on HN a while back, but for those that didn't see it the first time around: https://webrtcforthecurious.com/
Re: How Video Works
#6One thing i'd love to see added here is a blurb about the importance of the location of the video metadata in the file. Specifically that you need to have the metadata at the start of the file rather than the end of the file (which is the default) for low-latency playback on web. Explained: Freshly recorded MPEG (and almost all other container types) typically saves the header at the end of the file. This is the logi…
Yep, you make a really good point, thanks for the feedback. I think this bit would probably make sense to live in the upcoming "processing" section.
If anyone's interested, this is called the moov atom, and when you use "web playback" presets in tools like Handbrake, that's typically what it does is move that header to the beginning of the file. The progressive playback issues for files not optimized has improved somewhat when the file's host supports range requests, since browsers have gotten smart enough to try and check the end of the file for that header via range requests.
If you're interested in more along the codec/container line, one of my colleagues gave a talk on the internals of MP4 containers at Demuxed a few years ago[0] and another gave a Streaming Media keynote on the history of codecs and containers, particularly as they relate to online video[1].
[0] https://www.youtube.com/watch?v=iJAPTY3B7yE [1] https://www.youtube.com/watch?v=9Qo3WfsK4vc
Re: How Video Works
#7Thanks. I learned something. Maybe now I can fix our video playback on our website
Re: How Video Works
#8One thing i'd love to see added here is a blurb about the importance of the location of the video metadata in the file. Specifically that you need to have the metadata at the start of the file rather than the end of the file (which is the default) for low-latency playback on web. Explained: Freshly recorded MPEG (and almost all other container types) typically saves the header at the end of the file. This is the logi…
This is what the MP4 format calls the "moov atom".
Writing metadata at the end, instead of periodically interleaving it inside the file, is not only useless for web playback, but also for any creation process (i.e., live recording) which intends to call itself robust. Imagine recording a 1-hour long video, only to have some unrelated issue abruptly stopping it all (e.g. the application crashes, or the video camera suddenly loses power), thus rendering an unplayable file because the damned metadata didn't get to be written at the end of the file...
(luckily there are post-process methods that in some cases are able to restore such broken files, but still, a priori the file will be unplayable)
Re: How Video Works
#9One thing i'd love to see added here is a blurb about the importance of the location of the video metadata in the file. Specifically that you need to have the metadata at the start of the file rather than the end of the file (which is the default) for low-latency playback on web. Explained: Freshly recorded MPEG (and almost all other container types) typically saves the header at the end of the file. This is the logi…
> The reality is their existing solution backed by a CDN would also have worked if they encoded the videos correctly.
For folks who might not realize you can fix this post-encode, you can do this:
ffmpeg -i in.mp4 -c copy -map 0 -movflags +faststart out.mp4Re: How Video Works
#10One thing i'd love to see added here is a blurb about the importance of the location of the video metadata in the file. Specifically that you need to have the metadata at the start of the file rather than the end of the file (which is the default) for low-latency playback on web. Explained: Freshly recorded MPEG (and almost all other container types) typically saves the header at the end of the file. This is the logi…
Matroska is really great for streaming. It is a very featureful container, it can even be streamed over a lossy connection!
It is a shame that Chrome only allows it to contain vp8/opus. If it allowed all the codecs in mp4 I think it would see much wider adoption.