0

i want to know what's the big difference between the SAR and PAR, also how ffmpeg automatically deciding the DAR value with the SAR and video width & height.

why the SAR value is so important for a video aspect ratio?

few days ago, i just tried to merge some videos on ffmpeg and got some issue with the SAR and DAR (issue solved). i read some articles, questions but still not understood properly... specially the SAR and PAR.

Ayan
  • 1
  • Does this Q&A help? If not, could you edit your question and describe what you've understood, and what is still not clear? – dirkt Jan 30 '22 at 14:05
  • The SAR "Sample Aspect Ratio" is the actual pixel aspect ratio within the file. The DAR "Display Aspect Ratio" is essentially telling the player "you should scale this like so" to make it look right without actually re-encoding the file. https://superuser.com/a/908257/19943 – Mokubai Jan 30 '22 at 14:07

1 Answers1

1

There are two meanings of SAR: "Sample Aspect Ratio" (connected to mpeg4-avc terminology) and "Storage Aspect Ratio" (connected to mpeg2 terminology).

FFmpeg uses SAR in the meaning of "Sample Aspect Ratio" which is in fact PAR (from mpeg2 terminology) which means "Pixel Aspect Ratio" and defines "the shape of the pixel".

SAR as "Storage Aspect Ratio" defines "the frame size" and in that meaning SAR = DAR / PAR.

DAR is "Display Aspect Ratio" and defines "the ratio between the width and the height".

Lex
  • 343
  • Not the case. SAR is defined in MPEG-2 spec (ISO/IEC 13818-2) as sample aspect ratio. There is no PAR. Storage Aspect Ratio appears to be invented by some app vendor. – Gyan Jan 30 '22 at 16:01
  • @Gyan Thank you for the clarification. My knowledge was based on the different information I've found on the web in the past. This info could be also directly connected to the Ayan's problems - DAR, SAR and PAR abbreviations are confusing if the reader does not know what application the writer had in mind. If Ayan is referring only to FFmpeg then there is indeed no PAR but I can see PAR used for many people in their texts and this is what I tried to explain. – Lex Jan 30 '22 at 16:31