[mythtv-users] Suggest transcode settings

Thu Feb 13 08:08:52 UTC 2014

On 12 Feb 2014, at 13:49, Phil Wild <phil at holobyte.com.au> wrote:

> Hi,
> 
> I have a heap of home video I want to transcode. Currently the files are consuming around 12GB per hour. I'd like to get that down to around 2-3GB/hour without losing too much quality. I'd also prefer not to drop the resolution but rather increase/change compression algorithms etc.
> 
> I've been googling but haven't found anything really helpful yet. I'm sure one of the very smart people on here can give me an answer from their heads and save me a heap of time trial/erroring etc.
> 
> I'm guessing ffmpeg is the best tool for the job?
> 
> This is the output from exiftool for one of my files
> 
> phil at mythtv:/usbdata/videos/OurVideos/UnProcessed/2011-07-29-on/Original Media$ exiftool 2011-07-29\ 16_28_04\ \(id\).mov
> 
> ExifTool Version Number         : 8.60
> File Name                       : 2011-07-29 16_28_04 (id).mov
> Directory                       : .
> File Size                       : 167 MB
> File Modification Date/Time     : 2014:01:31 22:15:52+08:00
> File Permissions                : rw-rwxr--
> File Type                       : MOV
> MIME Type                       : video/quicktime
> Major Brand                     : Apple QuickTime (.MOV/QT)
> Minor Version                   : 0.0.0
> Compatible Brands               : qt
> Movie Data Size                 : 175276000
> Movie Header Version            : 0
> Create Date                     : 2014:01:31 14:15:52
> Modify Date                     : 2014:01:31 14:16:41
> Time Scale                      : 2500
> Duration                        : 0:00:49
> Preferred Rate                  : 1
> Preferred Volume                : 100.00%
> Preview Time                    : 0 s
> Preview Duration                : 0 s
> Poster Time                     : 0 s
> Selection Time                  : 0 s
> Selection Duration              : 0 s
> Current Time                    : 0 s
> Next Track ID                   : 4
> Track Header Version            : 0
> Track Create Date               : 2014:01:31 14:15:52
> Track Modify Date               : 2014:01:31 14:16:41
> Track ID                        : 1
> Track Duration                  : 0:00:49
> Track Layer                     : 0
> Track Volume                    : 0.00%
> Image Width                     : 1440
> Image Height                    : 1080
> Graphics Mode                   : ditherCopy
> Op Color                        : 32768 32768 32768
> Compressor ID                   : hdv3
> Vendor ID                       : Apple
> Source Image Width              : 1440
> Source Image Height             : 1080
> X Resolution                    : 72
> Y Resolution                    : 72
> Compressor Name                 : HDV 1080i50
> Bit Depth                       : 24
> Video Frame Rate                : 25
> Balance                         : 0
> Audio Channels                  : 2
> Audio Bits Per Sample           : 16
> Audio Sample Rate               : 48000
> Audio Format                    : wave
> Matrix Structure                : 1 0 0 0 1 0 0 0 1
> Media Header Version            : 0
> Media Create Date               : 2014:01:31 14:15:52
> Media Modify Date               : 2014:01:31 14:16:41
> Media Time Scale                : 2500
> Media Duration                  : 0:00:49
> Media Language Code             : und
> Gen Media Version               : 0
> Gen Flags                       : 0 0 0
> Gen Graphics Mode               : ditherCopy
> Gen Op Color                    : 32768 32768 32768
> Gen Balance                     : 0
> Handler Class                   : Data Handler
> Handler Vendor ID               : Apple
> Handler Description             : Core Media Data Handler
> Other Format                    : tmcd
> Handler Type                    : Metadata Tags
> Com Apple Proapps Camera ID (und-AU): 0x800460104f44e1c
> Com Apple Proapps Camera Name (und-AU): Sony HDV-VCR
> Com Apple Proapps Clip ID (und-AU): 748C35DF-2B0A-4F43-A692-12529F1D2A5D
> Com Apple Proapps Ingest Date Description (und-AU): 2014-01-31 22:15:52 +0800
> Com Apple Proapps Original Format (und-AU): HDV 1080i50
> Com Apple Proapps Media Rate (und-AU): 25
> Com Apple Proapps Timecode Format (und-AU): Non-Drop
> Creation Date (und-AU)          : 2011:07:29 16:28:04+08:00
> Make (und-AU)                   : Apple
> Model (und-AU)                  : Macmini5,1
> Software (und-AU)               : Mac OS X 10.9.1 (13B42)
> Avg Bitrate                     : 28.4 Mbps
> Image Size                      : 1440x1080
> Rotation                        : 0
ffmpeg -i your.mov  
will result in a much smaller file. By playing with the -crf value, lower values give better quality but bigger size. Use -crf instead of bitrates because parts of the video wit a lot of motion needs more bits then ‘talking heads’. -crf is used for constant quality by adding/removing bits where they are needed.
The human eye is more sensitive to vertical resolution then horizontal, therefore I use 896x720 instead of 1280x720. The same way your camera does, it uses 1440x1080 instead of 1920x1080.
Test for a few minutes with crf between 16 and 23, 23 being the default value.
ffmpeg -i your.mov -t 120 -vf yadif -c:a libfaac -ab 128k -c:v libx264 -g 50 -crf 22 -s 896x720 your_small_crf.mp4
This way you get 2 minutes with quality -crf 22 and see the results for your self. You are the ultimate judge of quality vs. size.
> 
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