Re: [Libav-user] Bitrate parameter ignored when writing videos

[Paul B Mahol]

On 8/10/16, Masneri, Stefano  wrote:
> I am trying to write an .mp4 video with a specified bitrate and gopsize set
> to 1.
> Apparently libavcodec ignores the settings I provide and creates a video
> with a much higher bitrate
>
> Here's the code I use to setup the output video:
>
>   m_pcVideoSt->codec->gop_size = m_iGopSize; /* emit one intra frame every
> m_iGopSize frames at most */
>   m_pcVideoSt->codec->pix_fmt = AV_PIX_FMT_YUV420P; /* default pix_fmt */
>   m_pcVideoSt->codec->max_b_frames = 1;
>   AVDictionary* pcOpts = nullptr;
>   int res1 = av_dict_set(, "b", "20k", 0);
>   int res = avcodec_open2(m_pcVideoSt->codec, codec, );
>
> m_pcVideoSt is of type AVStream*
>
> This is the output of ffprobe ran on the video I wrote:
>
> Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'testGray.mp4':
>   Metadata:
> major_brand : isom
> minor_version   : 512
> compatible_brands: isomiso2avc1mp41
> encoder : Lavf56.40.101
>   Duration: 00:00:20.00, start: 0.00, bitrate: 8905 kb/s
> Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p,
> 720x576, 8904 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
> Metadata:
>   handler_name: VideoHandler
>
> When watching the video, it seems that the quality is low for the first few
> frames, but then the quality gets much better (explaining the 8905Kb/s
> bitrate).
> Any idea on what I am missing?

Above I do not see relevant code that calls encoder.
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[Libav-user] Bitrate parameter ignored when writing videos

[Masneri, Stefano]

I am trying to write an .mp4 video with a specified bitrate and gopsize set to 
1.
Apparently libavcodec ignores the settings I provide and creates a video with a 
much higher bitrate

Here's the code I use to setup the output video:

  m_pcVideoSt->codec->gop_size = m_iGopSize; /* emit one intra frame every 
m_iGopSize frames at most */
  m_pcVideoSt->codec->pix_fmt = AV_PIX_FMT_YUV420P; /* default pix_fmt */
  m_pcVideoSt->codec->max_b_frames = 1;
  AVDictionary* pcOpts = nullptr;
  int res1 = av_dict_set(, "b", "20k", 0);
  int res = avcodec_open2(m_pcVideoSt->codec, codec, );

m_pcVideoSt is of type AVStream*

This is the output of ffprobe ran on the video I wrote:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'testGray.mp4':
  Metadata:
major_brand : isom
minor_version   : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf56.40.101
  Duration: 00:00:20.00, start: 0.00, bitrate: 8905 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 720x576, 
8904 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
Metadata:
  handler_name: VideoHandler

When watching the video, it seems that the quality is low for the first few 
frames, but then the quality gets much better (explaining the 8905Kb/s bitrate).
Any idea on what I am missing?
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Re: [Libav-user] Need to understand where demuxer for mp4 is hooked with h264 decoder ?

[ssshukla26]

Hi, It seems *demuxer for mp4* is sending data to decoder but without
*headers* (i.e. sps and pps) and the packets received is having only *size*
(first 4 bytes) at the beginning.

My decoder need sps and pps else its giving error that "No proper header"
while decoding. Can you please suggest what to be done ?



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