We are a small independent academic institution, that hosts a “digital collections” of digitized historical materials, on the web, using a custom in-house Rails app.
We’re getting into including some historical video content for the first time, and I didn’t have much experience with video, it required me to figure outa few things, that I’m going to document here. (Thanks to many folks from Code4Lib and Samvera communities who answered my questions, including mbklein, cjcolvar, and david.schober).
Some more things about us and our content:
- Our content at least initially will be mostly digitized VHS (480p, fairly low-visual-quality content), although we could also eventually have some digitized 16mm film and other content that could be HD.
- Our app is entirely cloud-hosted, mainly on heroku and AWS S3. We don’t manage any of our own servers at the OS level (say an EC2), and don’t want to except as a last resort (we don’t really have the in-house capacity to).
Our usage patterns are not necessarily typical for a commercial application! We have a lot (at least eventually we will) of fairly low-res/low-bitrate stuff (old VHSs!), it’s unclear how much will get viewed how often (a library/archives probably stores a lot more content as a proportion of content viewed than a commercial operation), and our revenue doesn’t increase as our content accesses do! So, warning to the general reader, our lense on things may or may not match a commercial enterprise’s. But if you are one of our peers in cultural heritage, you’re thinking, “I know, right?”
All of these notes are as of February 2022, if you are reading far in the future, some things may have changed. Also, I may have some things wrong, this is just what I have figured out, corrections welcome.
Standard Video Format: MP4 (h.264) with html5 video
I originally had in my head that maybe you needed to provide multiple video formats to hit all browsers — but it seems you don’t really anymore.
An MP4 using H.264 codec and AAC audio can be displayed in pretty much any browser of note with an html5 video tag.
There are newer/better/alternate video formats. Some terms (I’m not totally sure which of these are containers are which are codecs and which containers can go with which codecs!) include: WebM, Ogg, Theora, H.265, V8, and V9. Some of these are “better” in various ways (whether better licenses or better quality video at same filesize) — but none are yet supported across all common browsers.
You could choose to provide alternate formats so browsers that can use one of the newer formats will — but I think the days of needing to provide multiple formats to satisfy 99%+ of possible consumers appear gone. (Definitely forget about flash).
The vast majority of our cultural heritage peers I could find are using MP4. (Except for the minority using an adaptive bitrate streaming format…).
Another thing to know about H.264-MP4 is that even at the same screen size/resolution, the bitrate, and therefore the filesize (per second of footage) can vary quite a bit between files. This is because of the (lossy) compression in H.264. Some original source material may just be more compressible than others — not sure how much this comes into play. What definitely comes into play is that when encoding, you can choose to balance higher compression level vs higher quality (similar to in JPG). Most encoding software can let you choose set a maximum bitrate (sometimes using either a variable-bit-rate (VBR) or constant-bit-rate (CBR) algorithm), OR choose a “quality level” on some scale and the encoder will compress differently from second to second of footage, at whatever level will give you that level of “quality”.
An Aside: Tools: ffmpeg and ffprobe
ffmpeg (and its accompanying ffprobe analyzer) are amazing open source tools. They do almost anything. They are at the heart of most other video processing software.
ffprobe is invaluable for figuring out “what do I have here” if say given an mp4 file.
One thing I didn’t notice at first that is really neat is that both ffmpeg and ffprobe can take a URL as an input argument just about anywhere they can take a local file path. This can be very convenient if your video source material is, say, on S3. You don’t need to download it before feeding to ffmpeg or ffprobe, you can just give them a URL, leading to faster more efficient operations as ffmpeg/ffprobe take care of downloading only what they need as they need it. (ffprobe characterization can often happen from only the first portion of the file, for instance).
IF you need an adaptive bitrate streaming format: HLS will do
So then there are “streaming” formats, the two most popular being HLS or MPEG-DASH. While required if you are doing live-streaming, you also can use them for pre-recorded video (which is often called “video-on-demand” (VOD) in internet discussions/documentation, coming out of terminology used in commercial applications).
The main reason to do this is for the “adaptive bitrate” features. You can provide variants at various bitrates, and someone on a slow network (maybe a 3G cellphone) can still watch your video, just at lower resolution/visual quality. An adaptive bitrate streaming format can even change the resolution/quality in mid-view, if network conditions change. Perhaps you’ve noticed this watching commercial video over the internet.
Analogously to MP4, there are other adaptive bitrate streaming formats too, that may be superior in various ways to HLS, but don’t have as wide support. Like MPEG-DASH. At the moment, you can reach pretty much any browser in use with HLS, and of community/industry peers I found using an adaptive bitrate streaming format, HLS was the main one in use, usually presented without alternative sources.
But do we even need it?
At first I thought that one point of HLS was allowing better/more efficient seeking: When the viewer wants to jump to the middle of the video you don’t want to force the browser to download the whole video. But in fact, after more research I believe current browsers can seek in a static mp4 just fine using HTTP byte-range requests (important they are on a server that supports such!), so long as the MP4 was prepared with what ffmpeg calls faststart. (This is important! You can verify if a video is properly prepared by running mediainfo on it and looking for the
IsStreaming line in output; or by jumping through some hoops with ffmpeg).
It’s a bit hacky to do seeking with just http-hosted mp4s, but user-agents seem to have gotten pretty good at it. You may want to be sure any HTTP caching layer you are using can appropriately pass through and cache HTTP byte-range requests.
So, as far as I know, that leaves actual dynamic adaptive bitrate feature as the reason to use HLS. But you need that only if the MP4’s you’d be using otherwise are a higher bitrate than the lowest bitrate you’d be preparing for your inclusion in your HLS bundle. Like, if your original MP4 is only 500 kbps, and that’s the lowest bitrate you’d be including in your HLS package anyway… your original MP4 is already viewable on as slow a connection as your HLS preparation would be.
What is the lowest bitrate typically included as an option in HLS? i’ve found it hard to find advice on what variants to prepare for HLS distribution! In Avalon’s default configuration for creating HLS with ffmpeg, the lowest bitrate variant is 480p at 500 kbps. For more comparisons, if you turn on simulation of a slow connection in Chrome Dev Tools, Chrome says “Slow 3G” is about 400 kbps, and “Fast 3G” is about 1500 kbps. The lowest bitrate offered by AWS MediaConvert’s HLS presets is 400 kbps (for 270p or 360p) or 600kbps at 480p.
(In some cases these bitrates may be video-only; audio can add another 100-200kbps, depending on what quality you encode it at.)
I think if your original MP4 is around 500 kbps, there’s really no reason at all to use HLS. As it approaches 1500 kbps (1.5 Mbps)… you could consider creating HLS with a 500kbps variant, but also probably get away with serving most users adequately at the original bitrate (sorry to the slower end of cell phone network). As you start approaching 3Mbps, I’d start considering HLS, and if you have HD 720p or 1080p content (let alone 4K!) which can get up to 6 Mbps bitrates and even much higher — I think you’d probably be leaving users on not-the-fastest connections very frustrated without HLS.
This is me doing a lot of guessing, cause I haven’t found a lot of clear guidance on this!
As our originals are digitizations of VHS (and old sometimes degraded VHS at that), and started out pretty low-quality, our initial bitrates are fairly low. In one of our sample collections, the bitrates were around 1300bps — I’d say we probably don’t need HLS? Some of our digitized film was digitized in SD at around 2300 kbps — meh? But we had a couple films digitized at 1440p and 10 Mbps — okay, probably want to either downsample the access MP4, or use HLS.
MOST of our cultural heritage peers do not yet seem to be using HLS. In a sampling of videos found on DPLA, almost all were being delivered as MP4 (and usually fairly low-quality videos at under 2 Mbps, so that’s fine!). However, most of our samvera peers using avalon are probably using HLS.
So how do you create and serve HLS?
Once you create it, it’s actually just static files on disk, you can serve with a plain old static HTTP web server. You don’t need any kind of fancy media server to serve HLS! (Another misconception I started out not being sure of, that maybe used to be different, in the days when “RTP” and such were your only adaptive streaming options). An HLS copy on disk is one (or usually several)
.m3u8 manifest files, and a lot of
.ts files with chunked data referenced by the manifests.
You can (of course) use ffmpeg to create HLS. A lot of people do that happily, but it doesn’t work well for our cloud deployment — creating HLS takes too long for us to want to do it in a Rails background job on a heroku worker dyno, and we don’t want to be in the business of running our own servers otherwise.
Another thing some of our peers use is the wowza media server. We didn’t really look at that seriously either, I think our peers using it are at universities with enormous campus-wide site licenses for running it on-premises (which we don’t want to do), there might be a cloud-hosted SaaS version… but I just mention this product for completeness in case you are interested, it looked too “enterprisey” for our needs, and we didn’t significantly investigate.
The solutions we found and looked at that fit into the needs we had for our cloud-hosted application were:
- Use AWS Elemental MediaConvert to create the HLS variants, host on S3 and serve from there (probably with CloudFront, paying AWS data egrees fees for video watched). This is sort of like a cloud alternative to ffmpeg, you tell it exactly what HLS variants you want.
- AWS Elemental MediaPackage ends up working more like a “video server” — you just give it your originals, and get back an HLS URL, you leave the characteristics of the HLS variants up to the black box, and it creates them apparently on-the-fly as needed. You don’t pay for storage of any HLS variants, but do pay a non-trivial fee for every minute of video processed (potentially multiple times if it expires from cache and is watched again) on top of the AWS egrees fees.
- CloudFlare Stream is basically CloudFlare’s version of MediaPackage. They charge by second of footage instead of byte (for both storage and the equivalent of egress bandwidth), and it’s not cheap… whether it’s cheaper or more expensive than MediaPackage can depend on the bitrate of your material, and the usage patterns of viewing/storing. For our low-bitrate unpredictable-usage patterns, it looks to me likely to be end up more expensive? But not sure.
- Just upload them all to youtube and/or vimeo, and serve from there? Kind of crazy but it just might work? Could still be playing on our web pages, but they’re actually pointing at youtube or vimeo hosting the video…. While this has the attraction of being the only SaaS/PaaS solutions I know of that won’t have metered bandwidth (you don’t pay per minute viewed)… there are some limitations too. I couldn’t really find any peers doing this with historical cultural heritage materials.
I’m going to talk about each of these in somewhat more detail below, especially with regard to costs.
First a word on cost estimating of video streaming
One of our biggest concerns with beginning to include video in digital collections is cost. Especially because, serving out of S3/Cloudfront, or most (all?) other cloud options, we pay data egress costs for every minute of video viewed. As a non-profit educational institution, the more the video gets viewed, the more we’re achieving our mission — but our revenue doesn’t go up with minutes viewed, and it can really add up.
So that’s one the things we’re most interested in comparing between different HLS options.
But comparing it requires guessing at a bunch of metrics. Some that are easier to guess are: How many hours of video we’ll be storing; and How many hours we’ll be ingesting per month. Some services charge in bytes, some in hours; to convert from hours to bytes requires us to guess our average bitrate, which we can take a reasonable stab at. (Our digitized VHS is going to be fairly low quality, maybe 1500-2500 kbps).
Then there are the numbers that are a lot harder to guess — how many hours of video will be viewed a month? 100 hours? 1000? 10,000? I am not really sure what to expect, it’s the least under our control, it could grow almost unboundedly and cost us a lot of money. Similarly, If we offer full-file downloads, how many GB of video files will be downloaded a month?
Well, I made some guesses, and I made a spreadsheet that tried to estimate costs of various platforms under various scenarios. (There are also probably assumptions I don’t even realize I’m making not reflected in the spreadsheet that will effect costs!). Our initial estimates are pretty small for a typical enterprise, just hosting maybe 100 hours of video, maybe 200 hours viewed a month? Low-res VHS digitized material. (Our budget is also fairly sensitive to what would be very small amounts in a commercial enterprise!)
You can see/copy the spreadsheet here, and I’ll put a few words about each below.
Serve MP4 files from S3
The base case! Just serve plain MP4 files from S3 (probably with CloudFront in front). Sufficient if our MP4 bitrates are 500 kbps, maybe up to around 1.5 Mbps.
Our current app architecture actually keeps three copies of all data — production, a backup, and a sync’d staging environment. So that’s some S3 storage charges, initially estimated at just full-cost standard S3. There are essentially no “ingest” costs (some nominal cost to replicate production to our cross-region backup).
Then there are the standard AWS data egress costs — Cloudfront not actually that different from standard S3, until you get into trying to do bulk reserved purchases or something, but we’ll just estimate at the standard rate.
The storage costs will probably be included in any other solution too, since we’ll probably still keep our “canonical” cop(ies) on S3 regardless.
HLS via AWS Elemental MediaConvert
AWS Elemental MediaConvert is basically a transcoding service — think of it like ffmpeg transcoding but AWS-hosted SaaS. Your source needs to be on S3 (well, technically it can be a public URL elsewhere), you decide what variants you want to create, they are written to an S3 bucket.
Bandwidth costs are exactly the same as our base MP4 S3 case, since we’d still serving from Cloudfront — so essentially scales up with traffic exactly the same as our base case, which is nice. (hypothetically could be somewhat less bandwidth depending on how many users receive lower-bitrate variants via HLS, but we just estimated that everyone would get the high-quality one, as an upper bound).
We pay a bit more for storage (have to store the HLS derivatives, just standard S3 prices).
Then we pay an ingest cost to create the HLS, that is actually charged per minute (rather than per GB) — for SD, if we avoid “professional tier” features and stay no more than 30 fps, $0.0075 per minute of produced video (meaning the more HLS variants you create, the more you pay).
Since we probably will be digitizing a fairly small package per month, and there is no premium over standard S3 for bandwidth (our least predictable cost), this may be a safe option?
Also, because we know of at least one peer using AWS Elemental MediaConvert. (Northwestern University Libraries).
AWS Elemental MediaPackage
MediaPackage is basically an AWS media server offering. You can use it for live streaming, but we’re looking at the “Video on Demand” use case and pricing only. You just give it a source video, and it creates an HLS URL for it. (Among other possible streaming formats; HLS is the one we care about). You don’t (and I think can’t) tell it what bitrates/variants to create in the HLS stream, it just does what it thinks best. On the fly/on-demand, I think?
The pricing model includes a fairly expensive $0.05/GB packaging fee — that is, fee to create the stream. (why not per-minute like MediaConvert? I don’t know). This is charged on-demand: Not until someone tries to watch a video. If multiple people are watching the same video at the same time, you’ll only pay the packaging fee once as it’ll be cached in CloudFront. But I don’t know if it’s clear exactly how long it will remain cached in CloudFront — and I don’t know how to predict my viewers usage patterns anyway, how much they’ll end up watching the same videos taking advantage of cache — how many views will result in packaging fees vs cached views.
So taking a worst-case estimate of zero cache utilization, MediaPackage basically adds a 50% premium to our bandwidth costs. These being our least predictable and unbounded costs, this is a bit risky — if we have a lot of viewed minutes, that don’t cache well, this could end up being much more expensive than MediaConvert approach.
But, you don’t pay any storage fees for the HLS derivatives at all. If you had a large-stored-volume and relatively small viewed-minutes, MediaPackage could easily end up cheaper than doing it yourself with MediaConvert (as you can see in our spreadsheet). Plus, there’s just less to manage or code, you really just give it an S3 source URL, and get back an HLS URL, the end.
CloudFlare Stream is basically Cloudflare’s altenrative to MediaPackage. Similarly, it can be used for livestreaming, but we’re just looking at it for “video on demand”. Similarly, you basically just give it video and get back HLS URL (or possibly other streaming formats), without specifying the details.
The big difference is that CloudFlare meters per minute instead of per GB. For storage of a copy of “originals” in the Stream system, which is required– and we’d end up storing an extra copy in CloudFlare, since we’re still going to want our canonical copy in AWS. (Don’t know if we can do everything we’d need/want with a copy only in CloudFlare stream). And CloudFlare charges per minute for bandwidth from Stream too. (There is no ingest/packaging fee, and no cost for storage of derived HLS).
Since they charge per minute, how competitive it is really depends on your average bitrate, the higher your average bitrate the better a deal CloudFlare is compared to AWS! At an average bitrate of more than 1500kbps, the CloudFlare bandwidth cost starts beating AWS — at 10 MBps HD, it’s going to really beat it. But we’re looking at relatively low-quality SD under 1500kbps, so.
Whether CloudFlare Stream is more or less expensive than one of the AWS approaches is going to depend not only on bandwidth, but on your usage patterns (how much are you storing, how much are you ingesting a month) — from a bit more expensive to, in the right circumstances, a lot less expensive.
CloudFlare Stream has pretty much the convenience of AWS MediaPackage, except that we need to deal with getting a separate copy of originals into CloudFlare, with prepaid storage limits (you need to kind of sign up for what storage limit you want). Which is actually kind of inconvenient.
What if we used
YouTube or Vimeo though?
What if we host our videos on YouTube or Vimeo, and deliver them from there? Basically use them as a cloud hosted video server? I haven’t actually found any peers doing this with historical/cultural heritage/archival materials. But the obvious attraction is that these services don’t meter bandwidth, we could get out of paying higher egress/bandwidth as viewing usage goes up — our least predictable and potentially otherwise largest budget component.
The idea is that this would be basically invisible to the end-user, they’d still be looking at our digital collections app and an embedded viewer; ideally the items would not be findable in youtube/vimeo platform search or on google to a youtube/vimeo page. It would also be mostly invisible to content management staff, they’d ingest into our Digital Collections system same as ever, and our software would add to vimeo and get referencing links via vimeo API.
We’d just be using youtube or vimeo as a video server platform, really not too different from how one uses AWS MediaPackage or Cloudflare Stream.
Youtube is completely free, but, well, it’s youtube. It’s probably missing features we might want (I don’t think you can get a direct HLS link), has unclear/undocumented limits or risk of having your account terminated, you get what you pay for as far as support, etc.
Vimeo is more appealing. Features included (some possibly only in “pro” account and above) seem (am still at beggining of investigation) to include:
- HLS URLs we could use with whatever viewers we wanted, same viewers we’d be using with any other HLS URL.
- Also note direct video download links, if we want, so we can avoid bandwidth/egress charges on downloads too!
- Support for high-res videos, no problem, all the way up to 4K/HDR. (Although we don’t need that for this phase of VHS digitization)
- “team” accounts where multiple staff accounts can have access to Vimeo management of our content. (Only 3 accounts on $20/month “pro”, 10 on “Business” and higher)
- Unlisted/private settings that should keep our videos off of any vimeo searches or google. Even a “Hide from Vimeo” setting where the video cannot be viewed on a vimeo page at all, but only as embedded (say via HLS)!
- One issue, though, is that the HLS and video download links we do have probably won’t be signed/expiring — once someone has it, they have it and can share it (until/unless you delete the content from vimeo). This is probably fine for our public content use cases, but worth keeping in mind.
- An API that looks reasonable and full-featured.
Vimeo storage/ingest limits
The way Vimeo does price tiers/metering is a bit odd, especially at the $20/month “Pro” level. It’s listed as being limited to ingesting 20GB/week, and 1TB/year. But I guess it can hold as much content you want as long as you ingest it at no more than 20GB/week? Do I understand that right? For our relatively low-res SD content, let’s say at a 3Mbs bitrate — 20GB/week is about 15 hours/week — at our current planned capacity, we wouldn’t be ingesting more than that as a rule, although it’s a bit annoying that if we did, as an unusual spike, our software would have to handle the weekly rate limit.
At higher plans, the vimeo limits are total storage rather than weekly ingest. The “Business” plan at $50/month has 5TB total storage. At 3Mbs bitrate, that’s around 3700 hours of content. At our current optimistic planned ingest capacity, it would take us over 10 years to fill that up. If it were HD content at 10 Mbps, 5TB is around 1100 hours of content, which we might reach in 4 or 5 years at our current planned ingest rate.
The “Premium” plan lets you bump that up to 7TB for $75/month.
It’s certainly conceivable we could reach those limits — and even sooner if we increase our digitization/ingest capacity beyond what we’re starting with. I imagine at that point we’d have to talk to them about a custom “enterprise” plan, and hope they can work out something reasonable for a non-profit academic institution that just needs expanded storage limits.
I imagine we’d write our software so it could serve straight MP4 if the file wasn’t (yet?) in Vimeo, but would just use vimeo HLS (and download link?) URLs if it was.
It’s possible there will be additional unforeseen limitations or barriers once we get into an investigatory implementation, but this seems worth investigating.
Our initial implementation may just go with static MP4 files, for our relatively low-bitrate SD content.
When we are ready to explore streaming (which could be soon after MVP), I think we’d probably explore either vimeo? If not Vimeo… AWS MediaConvert is more “charted territory” as we have cooperating peers who have used it… but the possibility of MediaConvert or CloudFront Stream to be cheaper under some usage patterns is interesting. (And they are possibly somewhat simpler to implement). However, their risk of being much more expensive under other usage patterns may be too risky. Predictability of budget is really high-value in the non-profit world, which is a large part of our budgeting challenge here, the unpredictability of costs when increased usage means increased costs due to metered bandwidth/egress.