On 30 Oct 2015, at 03:40, Joel Lopez <[email protected]> wrote:
> Hi, > > I've been reading as much stuff as I can find what the best way to > encode key frame aligned videos. Hopefully you can help me fill in > the blanks. > > 1. Single or 2-pass encoding? I'm reading quality isn't affected > much and that it may be possible to have aligned key frames with > either one. What do you guys do? 2-pass in my opinion only makes sense when the resulting file has to be stored max-quality to finite storage medium. CD/DVD etc. Do some testing and look what % is saved and relate to the extra time/energy invested in that 2nd pass. > > A blog I found says I can just use this: > http://blog.streamroot.io/encode-multi-bitrate-videos-mpeg-dash-mse-based-media-players/ > > -x264opts 'keyint=24:min-keyint=24:no-scenecut’ FWIW how many times does one have changing bitrates as a result of differing line speeds and how many scene changes are there watching the same content. AFAIK blocking key frames on scene cuts/changes will result in more or less visible degraded quality. where differing in line speed quality and changing the used stream possibly results in ‘a few’ more or less frames. I don’t know which of the 2 is worse, haven’t tested. The scene change ‘problem’ will always be there while line speed quality differences occur probably only when ‘on the move’. My gut-feeling tells me the trade-offs of avoiding key frames on scene-cuts are greater. But as said haven’t tested this. > > Wowza says to do 2-passes like this: > http://www.wowza.com/forums/content.php?213-How-to-use-FFmpeg-with-Wowza-Media-Server-(MPEG-TS) > > ffmpeg -y -i bigbuckbunny_1500.mp4 -c:a libfaac -ac 2 -ab 64k -c:v > libx264 -preset:v veryfast -threads 0 -r 24 -g 48 -keyint_min 48 > -sc_threshold 0 -x264opts no-mbtree:bframes=1 -pass 1 -b:v 286k -s > 384x216 bigbuck-350k.mp4 > ffmpeg -y -i bigbuckbunny_1500.mp4 -c:a libfaac -ac 2 -ab 64k -c:v > libx264 -preset:v fast -threads 0 -r 24 -g 48 -keyint_min 48 > -sc_threshold 0 -x264opts no-mbtree:bframes=1 -pass 2 -b:v 286k -s > 384x216 bigbuck-350k.mp4 > ffmpeg -y -i bigbuckbunny_1500.mp4 -c:a libfaac -ac 2 -ab 64k -c:v > libx264 -preset:v fast -threads 0 -r 24 -g 48 -keyint_min 48 > -sc_threshold 0 -x264opts no-mbtree:bframes=1 -pass 2 -b:v 836k -s > 640x360 bigbuck-900k.mp4 > > > 2. I want my videos to work on as many devices as possible of course. > But I'm thinking of starting with 5 or 6 bit rates. We have only upto > 720p sources and stream on a Wowza server. What bitrates do you > stream? > > Apple seems to recommend 8 files > https://developer.apple.com/library/ios/technotes/tn2224/_index.html#//apple_ref/doc/uid/DTS40009745-CH1-SETTINGSFILES > > Kaltura says you can get up to 40 if you have different files for > desktop, iOS and Android. > http://knowledge.kaltura.com/best-practices-multi-device-transcoding > > Google does 5 versions with live encoder and I'm liking this. I've > seen they have 144p too on YouTube even though it's not listed. > https://support.google.com/youtube/answer/2853702?hl=en > > TLDR; > Single or 2pass for key frame alignment? > How many files and at what bitrates is a good starting point for > mobile and desktop? > > Thanks. > _______________________________________________ > ffmpeg-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/ffmpeg-user _______________________________________________ ffmpeg-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/ffmpeg-user
