the quality of beginning of compressed video

[MBlueSky]

Hi. When I compressed a video by ffmpeg the beginning of the compressed video has lower quality and the rest of that is normal. How can I fix it?

[ProWo]

What codec, what settings etc...

[MBlueSky]

What codec, what settings etc...

Codec is mp4, at Bitrate of 214kbps and I didn't use any special settings for the other parameters.

[ProWo]

Mp4 isn't a codec, but a container.
Post a mediainfo report (text mode) from your mp4 here.

[MBlueSky]

Mp4 isn't a codec, but a container.
Post a mediainfo report (text mode) from your mp4 here.

General
Complete name : ku_2.mp4
Format : MPEG-4
Format profile : Base Media
File size : 2.53 MiB
Duration : 58 s 700 ms
Overall bit rate : 361 kb/s
Writing application : Lavf58.76.100

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High
Format level : 2.1
Format settings, CABAC : Yes
Format settings, Referenc : 4 frames
Codec ID : avc1
Duration : 58 s 700 ms
Bit rate : 285 kb/s
Maximum bit rate : 288 kb/s
Width : 360 pixels
Height : 360 pixels
Display aspect ratio : 1.000
Frame rate mode : Constant
Frame rate : 30.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.073
Stream size : 2.02 MiB (80%)
Writing library : x264 core 158 r2984 3759fcb
Encoding settings : cabac=1 / ref=3 / deblock=1:0:0 / analyse=0x3:0x113 / me=hex / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=11 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=abr / mbtree=1 / bitrate=285 / ratetol=1.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Color range : Limited
Color primaries : BT.601 PAL
Transfer characteristics : BT.601
Matrix coefficients : BT.601
Codec configuration box : avcC

Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec
Codec ID : mp4a-40-2
Duration : 58 s 700 ms
Source duration : 58 s 746 ms
Bit rate mode : Constant
Bit rate : 64.1 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 44.1 kHz
Frame rate : 43.066 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 459 KiB (18%)
Source stream size : 460 KiB (18%)
Default : Yes
Alternate group : 1
mdhd_Duration : 58700

[jagabo]

Use two-pass encoding if you want bitrates that low. With single pass encoding the coded doesn't know how simple or complex the video is so it starts with low bitrate to make sure it doesn't over-allocate bits at the start of the video, then increases or decreases as it attempts to match the bitrate you specified.

Another possibility is that your video is very complex at the start and your requested bitrate is just too low for that part of the video. 2-pass encoding should help in this situation too.

[Cornucopia]

Particularly at scene boundaries and transitions, it might help if you can manually tweak the frame type and bitrate. But that requires an encoder that allows for manual frame-by-frame override adjustment.


Scott

[ProWo]

The bitrate is too low.
Use a CRF value (g.e. CRF 23 to start) instead of assign a fixed bitrate.
Read http://trac.ffmpeg.org/wiki/Encode/H.264

The simple way: use clever FFmpeg-GUI


[Attachment 60405 - Click to enlarge]

[MBlueSky]

Thank you all, guys