Add collision and video transcode documenation

releases/0.5.0.md

@@ -270,9 +270,28 @@ For all configuration options regarding media, see the example
 
 ### Improved Collision Resistance
 
+Previously, pict-rs relied on a sha256 hash of uploaded media's bytes in order to detect which files
+where the same, and which were unique. I have not heard of any existing problem with this behavior,
+however, as pict-rs becomes more widely deployed I want to ensure that deduplication does not happen
+erroneously. In the event of a hash collision between two different pieces of media, pict-rs would
+consider them duplicates and discard the newly uploaded file in favor of the one it already stored.
+This would lead to the wrong media being served for a user. In order to reduce the chances of a
+collission, pict-rs 0.5 now includes the media's file length and a marker indicating it's content
+type as part of it's unique identifier. This maintains the behavior of identical media being
+deduplicated, while making collisions far less likely to occur.
+
 
 ### Optional Video Transcoding
 
+In pict-rs 0.4, all videos that were uploaded were transcoded from their original format to either
+pict-rs' default format, or a format specified with configuration. pict-rs 0.5 removes the default
+"vp9" video codec, and allows uploaded videos to maintain their original codec and format, provided
+pict-rs supports it. This means uploaded h264, h265, vp8, vp9, and av1 videos no longer need to be
+decoded & encoded during the upload process aside from detecting their metadata.
+
+This behavior is enabled by default, but for administrators who have configured a non-default video
+codec, this can be enabled by removing the video_codec and audio_codec configurations.
+
 
 ### Library API Changes