ffmpeg DASH 编码：vp9 编解码器的比特率始终为 200k
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【中文标题】ffmpeg DASH 编码：vp9 编解码器的比特率始终为 200k【英文标题】：ffmpeg DASH encoding: always getting bitrate as 200k for vp9 codec 【发布时间】：2019-11-28 20:02:38 【问题描述】：我正在使用以下命令，之前输入 here: 来生成 DASH 文件：
ffmpeg -y -nostdin -loglevel error -i "$1" \
-map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:a\?:0 \
-maxrate:v:0 350k -bufsize:v:0 700k -c:v:0 libx264 -filter:v:0 "scale=320:-2" \
-maxrate:v:1 1000k -bufsize:v:1 2000k -c:v:1 libx264 -filter:v:1 "scale=640:-2" \
-maxrate:v:2 3000k -bufsize:v:2 6000k -c:v:2 libx264 -filter:v:2 "scale=1280:-2" \
-maxrate:v:3 300k -minrate:v:3 100k -bufsize:v:3 600k -c:v:3 libvpx-vp9 -filter:v:3 "scale=320:-2" \
-maxrate:v:4 1088k -minrate:v:4 200k -bufsize:v:4 2176k -c:v:4 libvpx-vp9 -filter:v:4 "scale=640:-2" \
-maxrate:v:5 1500k -minrate:v:5 300k -bufsize:v:5 3000k -c:v:5 libvpx-vp9 -filter:v:5 "scale=1280:-2" \
-use_timeline 1 -use_template 1 -adaptation_sets "id=0,streams=0,1,2 id=1,streams=3,4,5 id=2,streams=a" \
-threads 8 -crf 3 -seg_duration 5 -hls_init_time 1 -hls_time 5 -hls_playlist true -f dash "$2"
问题是，在输出中，vp9 编解码器的带宽始终为 200k（请参见下面的输出），而对于 h264 编解码器的相同视频带宽随着标准分辨率的不同而变化，而且相当小，我预计 vp9 会更少它压缩得更多。我已经使用多个不同的选项进行了测试，例如：-b:v、-deadline、-cpu-used-crf 等，但无法使用这些不同的值，我错过了什么？
样本输出mpd文件：
<?xml version="1.0" encoding="utf-8"?>
<MPD xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="urn:mpeg:dash:schema:mpd:2011"
xmlns:xlink="http://www.w3.org/1999/xlink"
xsi:schemaLocation="urn:mpeg:DASH:schema:MPD:2011 http://standards.iso.org/ittf/PubliclyAvailableStandards/MPEG-DASH_schema_files/DASH-MPD.xsd"
profiles="urn:mpeg:dash:profile:isoff-live:2011"
type="static"
mediaPresentationDuration="PT25.4S"
minBufferTime="PT15.0S">
<ProgramInformation>
</ProgramInformation>
<Period id="0" start="PT0.0S">
<AdaptationSet id="0" contentType="video" segmentAlignment="true" bitstreamSwitching="true" lang="und">
<Representation id="0" mimeType="video/mp4" codecs="avc1.64000c" band frameRate="24000/1001">
<SegmentTemplate timescale="24000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1">
<SegmentTimeline>
<S t="0" d="130130" />
<S d="250250" />
<S d="176176" />
<S d="54054" />
</SegmentTimeline>
</SegmentTemplate>
</Representation>
<Representation id="1" mimeType="video/mp4" codecs="avc1.64001e" band frameRate="24000/1001">
<SegmentTemplate timescale="24000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1">
<SegmentTimeline>
<S t="0" d="130130" />
<S d="250250" />
<S d="180180" />
<S d="50050" />
</SegmentTimeline>
</SegmentTemplate>
</Representation>
<Representation id="2" mimeType="video/mp4" codecs="avc1.64001f" band frameRate="24000/1001">
<SegmentTemplate timescale="24000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1">
<SegmentTimeline>
<S t="0" d="130130" />
<S d="250250" />
<S d="180180" />
<S d="50050" />
</SegmentTimeline>
</SegmentTemplate>
</Representation>
</AdaptationSet>
<AdaptationSet id="1" contentType="video" segmentAlignment="true" bitstreamSwitching="true" lang="und">
<Representation id="3" mimeType="video/mp4" codecs="vp09.00.11.08" band frameRate="24000/1001">
<SegmentTemplate timescale="24000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1">
<SegmentTimeline>
<S t="0" d="128128" r="3" />
<S d="98098" />
</SegmentTimeline>
</SegmentTemplate>
</Representation>
<Representation id="4" mimeType="video/mp4" codecs="vp09.00.21.08" band frameRate="24000/1001">
<SegmentTemplate timescale="24000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1">
<SegmentTimeline>
<S t="0" d="128128" r="3" />
<S d="98098" />
</SegmentTimeline>
</SegmentTemplate>
</Representation>
<Representation id="5" mimeType="video/mp4" codecs="vp09.00.31.08" band frameRate="24000/1001">
<SegmentTemplate timescale="24000" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1">
<SegmentTimeline>
<S t="0" d="128128" r="3" />
<S d="98098" />
</SegmentTimeline>
</SegmentTemplate>
</Representation>
</AdaptationSet>
<AdaptationSet id="2" contentType="audio" segmentAlignment="true" bitstreamSwitching="true" lang="eng">
<Representation id="6" mimeType="audio/mp4" codecs="mp4a.40.2" band audiosamplingRate="44100">
<AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2" />
<SegmentTemplate timescale="44100" initialization="init-stream$RepresentationID$.m4s" media="chunk-stream$RepresentationID$-$Number%05d$.m4s" startNumber="1">
<SegmentTimeline>
<S t="0" d="235520" r="3" />
<S d="180224" />
</SegmentTimeline>
</SegmentTemplate>
</Representation>
</AdaptationSet>
</Period>
</MPD>
我正在使用这个video，但我尝试过的所有大约 30 秒的视频都是一样的。
【问题讨论】：
【参考方案1】：从这个answer 获得帮助，看来我必须使用Two-pass 编码或Constant Quality 编码。
当我使用Constant Quality 编码时，我删除了bufSize、minRate 等并将-b:v 设置为零，我能够生成不默认为200k 的可变比特率，下面的示例命令，我将测试Two-pass 编码也是如此。
ffmpeg -y -nostdin -loglevel error -i "$1" \
-map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:v:0 -map 0:a\?:0 \
-maxrate:v:0 350k -bufsize:v:0 700k -c:v:0 libx264 -filter:v:0 "scale=320:-2" \
-maxrate:v:1 1000k -bufsize:v:1 2000k -c:v:1 libx264 -filter:v:1 "scale=640:-2" \
-maxrate:v:2 3000k -bufsize:v:2 6000k -c:v:2 libx264 -filter:v:2 "scale=1280:-2" \
-b:v:3 0 -c:v:3 libvpx-vp9 -filter:v:3 "scale=320:-2" \
-b:v:4 0 -c:v:4 libvpx-vp9 -filter:v:4 "scale=640:-2" \
-b:v:5 0 -c:v:5 libvpx-vp9 -filter:v:5 "scale=1280:-2" \
-use_timeline 1 -use_template 1 -adaptation_sets "id=0,streams=0,1,2 id=1,streams=3,4,5 id=2,streams=a" \
-threads 32 -deadline best -cpu-used 1 -crf 3 -seg_duration 5 -hls_init_time 1 -hls_time 5 -hls_playlist true -f dash "$2"
【讨论】：
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