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Thread: Changing video size from 1080p to 720p - what new bitrate should I use?

  1. #1

    Question Changing video size from 1080p to 720p - what new bitrate should I use?

    I am converting a video taken on my JVC Everio GZ-HD620 from 1080p to 720p using Windows Live Movie Maker.

    I believe the original video bitrate is around 22.7 Mbps (according to KMPlayer).

    WLMM wants to know what bitrate it should use when it sizes it down to 720p (in kbps).

    What would you use?

    Code:
    L:\Desktop\Videos To Sort\Camcorder\00016.MTS
       General #0
          ID : 0 (0x0)
          Complete name : L:\Desktop\Videos To Sort\Camcorder\00016.MTS
          Format : BDAV
          Format/Info : Blu-ray Video
          File size : 249 MiB
          Duration : 1mn 27s
          Overall bit rate : 24.0 Mbps
          Maximum Overall bit rate : 24.0 Mbps
       Video #4113
          ID : 4113 (0x1011)
          Menu ID : 1 (0x1)
          Format : AVC
          Format/Info : Advanced Video Codec
          Format profile : High@L4.0
          Format settings, CABAC : No
          Format settings, ReFrames : 2 frames
          Format settings, GOP : M=1, N=24
          Codec ID : 27
          Duration : 1mn 27s
          Bit rate mode : Variable
          Bit rate : 22.8 Mbps
          Maximum bit rate : 22.6 Mbps
          Width : 1 920 pixels
          Height : 1 080 pixels
          Display aspect ratio : 16:9
          Frame rate : 25.000 fps
          Color space : YUV
          Chroma subsampling : 4:2:0
          Bit depth : 8 bits
          Scan type : Interlaced
          Scan order : Top Field First
          Bits/(Pixel*Frame) : 0.439
          Stream size : 237 MiB (95%)
       Audio #4352
          ID : 4352 (0x1100)
          Menu ID : 1 (0x1)
          Format : AC-3
          Format/Info : Audio Coding 3
          Mode extension : CM (complete main)
          Codec ID : 129
          Duration : 1mn 27s
          Bit rate mode : Constant
          Bit rate : 256 Kbps
          Channel(s) : 2 channels
          Channel positions : Front: L R
          Sampling rate : 48.0 KHz
          Bit depth : 16 bits
          Compression mode : Lossy
          Delay relative to video : -40ms
          Stream size : 2.67 MiB (1%)
       Text #4608
          ID : 4608 (0x1200)
          Menu ID : 1 (0x1)
          Format : PGS
          Codec ID : 144
          Duration : 1mn 26s
          Delay relative to video : -40ms

  2. #2

    Default

    The bit rate of the original video is 24Mbps, but it's a variable bit rate rather than constant so your getting it a bit lower. Your video is also a Long GOP structure, i.e. it doesn't have the full information for every frame, some frames are referencing information on other frames.

    Ideally you'll wan't to set it to 24Mbps, but it would also be a good idea to use an intermediate codec that doesn't use a Long GOP structure for editing. I have no idea how/if Windows Live Movie Maker can work with Long GOP, I can imagine it can as most users will be editing straight out the camera. I also have no idea what codecs it can read. If it can use them it would be a good idea to download the free Avid codecs (available on their site) and convert to 35Mbps Avid DNxHD for editing.

    David.

  3. #3

    Default

    Quote Originally Posted by david walsh View Post
    The bit rate of the original video is 24Mbps, but it's a variable bit rate rather than constant so your getting it a bit lower. Your video is also a Long GOP structure, i.e. it doesn't have the full information for every frame, some frames are referencing information on other frames.

    Ideally you'll wan't to set it to 24Mbps, but it would also be a good idea to use an intermediate codec that doesn't use a Long GOP structure for editing. I have no idea how/if Windows Live Movie Maker can work with Long GOP, I can imagine it can as most users will be editing straight out the camera. I also have no idea what codecs it can read. If it can use them it would be a good idea to download the free Avid codecs (available on their site) and convert to 35Mbps Avid DNxHD for editing.

    David.
    I am sizing it down to 720p purely so After Effects CS5.5 doesn't take 40 minutes to stabilize the video. Takes around 7 minutes @ 720p.

  4. #4

    Default

    You can convert it to 720p in After Effects too, what ever you use I have a strong feeling that if you convert to an intermediate codec you will find that After effects doesn't take so long, I can't be certain as I never work with Long GOP codecs in editing, but it makes a lot of sense that it will. It could be worth a try as it might let you keep your 1080p. After Effects can definitely work with Avid DNxHD codecs, but if your then going back to Movie Maker to edit (strange combination) I don't know, you'd need to try and see.

    David.

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