Final Cut Studio. Native Long-GOP Editing. Brett R. Halle Sr. Director, Pro Video Applications Engineering Apple Computer, Inc.

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1 Final Cut Studio Native Long-GOP Editing Brett R. Halle Sr. Director, Pro Video Applications Engineering Apple Computer, Inc. HPA Technology Retreat - February 24, 2006

2 Introduction NLE traditionally based on I-frame formats 2004: Long-GOP HDV burst on the scene 2005: Native HDV editing in FCP v5 Intermediate-codec HDV editing in FCE & imovie Let s examine: Can Native HDV = truly pro performance & results? Pros/cons of Native vs Intermediate-codec HDV editing

3 First, some preliminaries...

4 Two Approaches to HDV Editing Edit with an Intermediate codec Transcode to a (typically) I-frame format during capture Use traditional I-frame-based editing techniques Transcode back to long-gop for output back to device Edit Natively* Solve the hard problems of dealing directly with Long-GOP at every phase of the NLE process *Some vendors use Native merely to mean built-in to their NLE, i.e., not supplied by a 3rd party

5 Native Editing Shoot, edit, and output in the same format Camera-native (DV, HDV, DVCPRO HD) Camera-native (DV, HDV, DVCPRO HD) Shoot Edit Output

6 Key Principles of Native Editing Preview op ns (RT Playback, Scrub, etc) are decode-only Re-compress only frames modified by edits Re-compress matters only at final rendering time Optimize encoder to minimize re-compression degradation

Example of Native Device I/O Baseband vs Device-native compressed Desktop NLE DVCPRO-HD Device 1920 1280 HD-SDI

7 Example of Native Device I/O Baseband vs Device-native compressed Desktop NLE DVCPRO-HD Device HD-SDI Card HD-SDI Up/down Sample Codec Tape FireWire Native (compressed domain) path avoids I/O re-encoding generation loss

8 I-frame vs Long-GOP Data Rates Table shown for 1080i60 format Codec Bit rate (Mbit/s) HDD Xfer (MByte/s) Storage (GByte/hr) DVCPRO-HD (for reference) HDV Long-GOP AIC (transcode of HDV Long-GOP) ~110* ~13* ~50* *Apple Intermediate Codec (AIC) uses VBR encoding HDV rates attractive for laptops & low-cost hard drives

9 HDV MPEG-2 GOPs GOP = Group of Pictures P B B I B B P B JVC 720p30 6-frame Closed GOP Worst-case random access: 3 frames to decode P B B I B B P B B P B B P B B P B B I Sony 1080i60 15-frame Open GOP Worst-case random access: 7 frames to decode

10 Next, consider basic NLE operations, comparing I-frame to Long-GOP...

11 Basic NLE Operations 1. Video input (capture, import) 2. Video editing RT playback with FX Scrubbing Jog/shuttle (JKL) 3. Video output (PTV, export) All operations complicated by long-gop formats

12 Video Input I-frame: capture at any in/out frames in out Long-GOP: extend capture to GOP boundaries in out User perceives only in/out points QuickTime does the bookkeeping

13 Editing: RT Playback I-frame simple seamless playback clip 1 clip 2 cut Long-GOP cuts will not always be on GOP boundaries clip 1 clip 2 cut Partial GOP precedes cut point

14 Long-GOP RT Playback Detailed look at previous slide clip 1...P B B I B B P B B P... P B cut point...p B B I B B P B B P... P B... clip 2 partial GOP Seamless RT playback achieved as follows: Extra frames to be decoded prior to Clip 2 cut point Trick: schedule decoding in advance, as with transitions

15 Editing: RT Playback with FX I-frame cross dissolve example cross dissolve clip 1 clip 2 Within cross-dissolve, decode & mix frames from both clips Long GOP cross dissolve example cross clip 1 dissolve clip 2 Decode partial GOP prior to cross dissolve boundary

16 Long-GOP Scrubbing & Jog/Shuttle Non-GOP-aligned clips within a cross-dissolve P B B I B B P B B P P B P B B I B B P B B P P B Fast Rev: the difficult direction Speed playback through an effect, fwd or rev Decode, mix, & display every Nth (red) frame Secret: buffer recent frames in both directions FCP responsiveness is remarkably fluid

17 Video Output to HDV Tape Encoder variable rate Buffer HDV tape (constant rate channel) HDV tape imposes strict CBR requirement If using intermediate codec, entire timeline must be reencoded to long-gop CBR, in order to output to HDV tape

18 Video Output to HDV Tape Long-GOP Case: Conformant Re-encoding As with Native I-frame editing, (most) unmodified frames do not get re-encoded But neighborhood around cuts must be re-encoded to properly formed GOPs CBR buffer fullness must be continuous at boundaries clip 1 cut point clip 2 re-encoded GOPs

19 AIC vs. Native HDV Quality Measurement of video-out to HDV tape For long-gop Native timeline, measure average PSNR of re-encoded frames around cut clip 1 clip 2 cut edit mild quality loss from AIC transcoding For AIC timeline, measure average PSNR compounded from (a) AIC transcode at capture time, and (b) Long-GOP re-encode of entire timeline at video-out time measure same frames quality loss from Long-GOP re-encoding clip 1 clip 2 cut edit

20 AIC vs. Native HDV Quality Measurement of video-out to HDV tape Timeline Codec Capture PSNR + Long-GOP re-encode for output Frames with zero quality loss AIC db (1.8 levels avg) 35.6 db (4.2 levels avg) None Native Long-GOP No transcode Infinite db (0 levels) 36.1 db (4.0 levels avg) Unedited frames: Infinite db (0 levels) Native HDV beats AIC on quality Slightly around edit boundaries Substantially, for unmodified footage Measurements taken from unusually challenging material

21 Performance Comparison 1080i60 PowerMac G5 Quad 2.5GHz Codec High-Quality Decode (simultaneous streams) Medium-Quality Decode (simultaneous streams) High-Quality Encode (frames per second) DVCPRO HD* ~130 AIC* ~170 Native HDV ~20 * DVCPRO HD & AIC require RAID for multistream playback Native HDV performance! DVCPRO HD AIC at Medium quality is slightly better DVCPRO HD & AIC require RAID for multi-stream playback HDV encoding slow, but Native only re-encodes the changes

22 Conclusions Native HDV Long-GOP NLE highly effective RT performance competitive with I-frame Scrubbing/JKL performance is highly responsive Output-to-tape quality better than intermediate Principles and methods should be extended to future formats, like H.264

HDV Editing Made Simple (And Fast) Convergent Design

HDV Editing Made Simple (And Fast) Convergent Design www.convergent-design.com HDV Editing Made Simple (And Fast) Two Simple Rules 1. Convert HDV I-Frame CODEC 2. Keep it All Digital Rule #1 Convert HDV