> On 12 May 2015, at 13:50, Werner Robitza <[email protected]> wrote: > > On Tue, May 12, 2015 at 11:47 AM, Henk D. Schoneveld <[email protected]> > wrote: >> Would you be so kind to explain why to NOT use the crf option? > > CRF is essentially a constant quality mode, which results in variable > bitrate depending on the spatiotemporal complexity of the scenes. Your goal is max quality within a given link-capacity I assume. Upfront choosing an arbitrary bitrate to achieve max possible quality seems sub-optimal/contradictionary to me. A. to many bits for talking heads B. to few bits for action dominant events. > For > streaming purposes, this is not ideal, since your adaptive streaming > client assumes that a segment encoded at a target bitrate of x kBit/s > is can actually be transmitted over a link with x kBit/s throughput. Where both the stream and link bitrate are averages. A stream consists of I and P and sometimes B frames, the size of these individual frames differ in size. For example choosing a small GOP-size, with relatively more I-frames, will result in more or less 'avoidable' relatively lower average quality. > > If you want to make sure you're not exceeding a certain bandwidth, the > VBV encoding mode is probably the best option (see also > https://trac.ffmpeg.org/wiki/EncodingForStreamingSites). Therefore, > set -maxrate and -bufsize. > > A single-pass constant bitrate will not generally be more stable than > CRF, but it should be less spikey. > > See this chart for a comparison between CRF, single-pass CBR and > single-pass CBR with -maxrate set: http://i.imgur.com/GxTW4Jy.png > y-axis is the frame size, moving average of 120 frames. I see the difference between the methods, but I don’t really understand what it’s trying to tel me. What does the X-axis say, total stream-size/#frames/ ? > _______________________________________________ > ffmpeg-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/ffmpeg-user
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