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choosing-crf-value-for-encoder.md (3279B)


      1 # Choosing CRF value for encoder
      2 
      3 ## Context
      4 Bandwidth usage by the Jami application is not optimal for all types of connections. Indeed, in some cases, the user experience is not good (satellite connection, ...) despite the bandwidth management algorithm.
      5 
      6 ## Observation
      7 It is not necessary to aim for an optimal quality (CRF < 20) because beyond that, the visual perception is almost similar while the data flow (bitrate) required is much higher.
      8 
      9 ## Objective
     10 The purpose of this document is to verify the impact of a change in video quality with the CRF parameter of the encoder.
     11 
     12 ## Test
     13 These tests were performed by comparing :
     14 - The first one encoded with Jami's current parameters
     15 - The second encoded with a lower quality
     16 
     17 Each of these tests were performed for the following resolutions: 1080p, 720p and 436p.
     18 
     19 For each of these resolutions several bitrates have been used:
     20 - 300 Kbit/s (Jami low value)
     21 - 1.5 Mbit/s (Intermediate value)
     22 - 6 Mbit/s (High value)
     23 
     24 The graphs show the evolution of the bitrate with the file being tested (resolution and specific set bitrate).
     25 
     26 A visual comparison (side by side) was made for each test.
     27 
     28 Thanks to this test we can estimate the bitrate that will be emitted in Jami according to the chosen parameters. We also have an overview of the visual quality.
     29 
     30 * * *
     31 
     32 1080p / 300 kbit/s / CRF28
     33 ![image](encoder01.png)
     34 1080p / 300 kbit/s / CRF38
     35 ![image](encoder02.png)
     36 
     37 Visual comparison (CRF28 a gauche / CRF38 a droite)
     38 https://nextcloud.savoirfairelinux.com/index.php/s/twzPmT3MRPjQ3b7
     39 
     40 1080p / 1.5 Mbps / CRF22
     41 ![image](encoder03.png)
     42 1080p / 1.5 Mbit/s / CRF30
     43 ![image](encoder04.png)
     44 
     45 Visual comparison (CRF22 left / CRF30 right)
     46 https://nextcloud.savoirfairelinux.com/index.php/s/XK6Ef3rwBFriRXT
     47 
     48  1080p / 6 Mbps / CRF17
     49 ![image](encoder05.png)
     50  1080p / 6 Mbit/s / CRF23
     51 ![image](encoder06.png)
     52 
     53 Visual comparison (CRF17 on the left / CRF23 on the right)
     54 https://nextcloud.savoirfairelinux.com/index.php/s/RG3TksjQKtMorW5
     55 
     56 * * *
     57 
     58 720p / 300 kbps / CRF28
     59 ![image](encoder07.png)
     60 720p / 300 kbit/s / CRF38
     61 ![image](encoder08.png)
     62 Visual comparison (CRF28 left / CRF38 right)
     63 https://nextcloud.savoirfairelinux.com/index.php/s/Z4T6EzGqyyWTJ9f
     64 
     65 720p / 1.5 Mbps / CRF22
     66 ![image](encoder09.png)
     67 720p / 1.5 Mbit/s / CRF30 (Test with reduced CRF)
     68 ![image](encoder10.png)
     69 
     70 Visual comparison (CRF22 left / CRF30 right)
     71 https://nextcloud.savoirfairelinux.com/index.php/s/H2Z5NQT3zJ9wzod
     72 
     73 720p / 6 Mbps / CRF17
     74 ![image](encoder11.png)
     75 720p / 6 Mbit/s / CRF23
     76 ![image](encoder12.png)
     77 
     78 Visual comparison (CRF17 left / CRF23 right)
     79 https://nextcloud.savoirfairelinux.com/index.php/s/gACSARfHjAKqgRR
     80 
     81 * * *
     82 
     83 436p / 300 kbps / CRF28
     84 ![image](encoder13.png)
     85 436p / 300 kbit/s / CRF38
     86 ![image](encoder14.png)
     87 
     88 Visual comparison (CRF28 left / CRF38 right)
     89 https://nextcloud.savoirfairelinux.com/index.php/s/gj9CpQox5fiaWMT
     90 
     91 436p / 1.5 Mbps / CRF22
     92 ![image](encoder15.png)
     93 436p / 1.5 Mbit/s / CRF30
     94 ![image](encoder16.png)
     95 
     96 Visual comparison (CRF22 left / CRF30 right)
     97 https://nextcloud.savoirfairelinux.com/index.php/s/BeCaqs2rMRpNQwS
     98 
     99 436p / 6 Mbps / CRF17
    100 ![image](encoder17.png)
    101 436p / 6 Mbit/s / CRF23
    102 ![image](encoder18.png)
    103 
    104 Visual comparison (CRF17 left / CRF23 right)
    105 https://nextcloud.savoirfairelinux.com/index.php/s/KLeXq9NeLKTfyqs