gstreamer/subprojects/gst-editing-services/docs/design/encoding-research.txt

GStreamer: Research into encoding and muxing
--------------------------------------------

Use Cases
---------

 This is a list of various use-cases where encoding/muxing is being
 used.

* Transcoding

  The goal is to convert with as minimal loss of quality any input
  file for a target use.
  A specific variant of this is transmuxing (see below).

  Example applications: Arista, Transmageddon

* Rendering timelines

  The incoming streams are a collection of various segments that need
  to be rendered.
  Those segments can vary in nature (i.e. the video width/height can
  change).
  This requires the use of identiy with the single-segment property
  activated to transform the incoming collection of segments to a
  single continuous segment.

  Example applications: Pitivi, Jokosher

* Encoding of live sources

  The major risk to take into account is the encoder not encoding the
  incoming stream fast enough. This is outside of the scope of
  encodebin, and should be solved by using queues between the sources
  and encodebin, as well as implementing QoS in encoders and sources
  (the encoders emitting QoS events, and the upstream elements
  adapting themselves accordingly).

  Example applications: camerabin, cheese

* Screencasting applications

  This is similar to encoding of live sources.
  The difference being that due to the nature of the source (size and
  amount/frequency of updates) one might want to do the encoding in
  two parts:
  * The actual live capture is encoded with a 'almost-lossless' codec
  (such as huffyuv)
  * Once the capture is done, the file created in the first step is
  then rendered to the desired target format.

  Fixing sources to only emit region-updates and having encoders
  capable of encoding those streams would fix the need for the first
  step but is outside of the scope of encodebin.

  Example applications: Istanbul, gnome-shell, recordmydesktop

* Live transcoding

  This is the case of an incoming live stream which will be
  broadcasted/transmitted live.
  One issue to take into account is to reduce the encoding latency to
  a minimum. This should mostly be done by picking low-latency
  encoders.

  Example applications: Rygel, Coherence

* Transmuxing

  Given a certain file, the aim is to remux the contents WITHOUT
  decoding into either a different container format or the same
  container format.
  Remuxing into the same container format is useful when the file was
  not created properly (for example, the index is missing).
  Whenever available, parsers should be applied on the encoded streams
  to validate and/or fix the streams before muxing them.

  Metadata from the original file must be kept in the newly created
  file.

  Example applications: Arista, Transmaggedon

* Loss-less cutting

  Given a certain file, the aim is to extract a certain part of the
  file without going through the process of decoding and re-encoding
  that file.
  This is similar to the transmuxing use-case.

  Example applications: Pitivi, Transmageddon, Arista, ...

* Multi-pass encoding

  Some encoders allow doing a multi-pass encoding.
  The initial pass(es) are only used to collect encoding estimates and
  are not actually muxed and outputted.
  The final pass uses previously collected information, and the output
  is then muxed and outputted.

* Archiving and intermediary format

  The requirement is to have lossless

* CD ripping

  Example applications: Sound-juicer

* DVD ripping

  Example application: Thoggen