Easy - just submit your video to Flowplayer Drive, and everything is done
for you automagically!
Transcoding to the required formats in optimal quality using parameters
individually chosen for each of your videos, plus CDN distribution and storage
or your originals. Try it out for free.
For those determined not to delegate this painful task a few tips are to follow.
General advice
Always bear in mind that encoding for delivery over the wire differs
fundamentally from encoding for a desktop viewing program. Your content has to
pass through the needle hole of a connection whose speed is not under your
control.
The results will and can only be a compromise between desired quality and
delivery speed achieved by lossy compression. Moreover they will vary depending
on the content of the original. A simple headshot is way more compression
friendly than a movie containing high motion scenes and/or pan shots. You
have to decide on which side of the scales you make more sacrifices, also in
view of your target audience and the assumed speed of their connections.
Be extremely miserly about bitrate and dimensions! Downscaling is a waste of
resources and often a video in the dimensions of the player container element
on the page displays reasonably well in fullscreen too.
Encode to a constant frame rate. Variable frame rate will break playback in
various scenarios, depending on engine, browser or platform.
If the input video is interlaced, you should apply a deinterlace filter.
If the input video does not have a sample ratio of 1/1 (square pixels), you
must apply a filter enforcing a sample ratio of 1/1 because some versions of
Internet Explorer cannot handle anamorphic MP4 and Flash is agnostic of
display aspect ratio, knows only about width and height.
Assuming your original video has an aspect ratio of 16/9 and keeping the above
caveats in mind you should aim for:
a resolution of 640x360 pixels
an average video bitrate between 400 and 1000 kilobits per second
an average audio bitrate between 40 and 80 kilobits per second
Take your time to try out various encoding settings on a small sample
representative of your content. Good transcoding programs offer a constant
quality switch. Try it and inspect the resulting bitrate. For the final encode
use 2-pass encoding which distributes the bitrate better while keeping a good
quality balance.
Codecs
MP4, WEBM and OGG are the containers for the following video and audio codecs:
We did not cover the MPEG-4 Visual or MPEG-4 Part 2 video codec
because it is not suitable as Flash fallback and will also not play in
Internet Explorer in HTML5 mode. To avoid bad surprises encode
to the more modern MPEG-4 AVC.
Ogg video
Unless you want to cover all your bases, consider omitting it. Except for a few
corner cases concerning older browsers where you can failover to MP4
playback in Flash mode, either WEBM or MP4 will do the job as
well, and better.
MP4 and metadata
H.264 encoded videos carry their metadata - duration, frame rate etc. - in the
so called "moov atom".
By default encoding programs will insert the moov atom at the end of the video
file which is suitable for playback of a local file in a desktop program.
However, any kind of progressive download requires the metadata to be available
right away for immediate playback. Otherwise the player has to wait for the
entire video to be downloaded before playback starts.
Make sure to select an option in your transcoding program which puts the moov
atom at the beginning of the file!
In case you already have a lot of MP4 videos with the moov atom at the end of
the file, use a dedicated program such as QTIndexSwapper or
MOOV Relocator to move it to the beginning.
MP4 for iOS and mobile devices
MPEG-4 AVC is a powerful codec which allows very effective compression at
various profiles and levels. As higher profiles and levels are decoding
intensive, they are not supported by mobile devices to ease their processor
workload.
Let's take iOS as an example: Even the latest iPads will only play videos
encoded at H.264 Main profile Level 3.1. But if you want to cater safely for the
widest audience including viewers with iPhones and iPods and older iOS versions
you should stick with:
Resolution of maximum 640px width and maximum 480px height
Encoding samples
To give you an idea to what the above considerations lead we choose the
commandline syntax of the FFmpeg program - there are also graphical
frontends for FFmpeg, like Handbrake or ffmpegX (for Mac OS). There are
many other transcoding programs around, and you should of course choose one you
feel most comfortable with. Be aware though that often the quality of the
program is directly proportional to its learning curve. It's also recommended
to use the very latest version of the respective program because development in
this area is moving fast.
In the following replace x in -pass x with 1 and 2 for the first and
second pass/run respectively. We assume the original movie in.suffix has an
aspect ratio of 16/9 and a frame rate of 25 frames per second.
Disclaimer: The above commandlines are very basic, and the syntax may differ
in older FFmpeg versions. This cannot be the place for detailed information on
how to handle the transcoding program(s) of your choice. Please consult the
respective manuals, online documentation or mailing lists for in-depth advice
regarding your transcoding software.
Comments
Post a Comment