<p>Intra frames (I-frames, keyframes) are <em>independent of other frames</em> - they contain the complete information for reconstructing the frame's image. There is no need for reading other frames and computing from them.</p>

<p>So it's about a <em>speed</em>, not about a quality. On the other hand, more intra frames, grater size of the file. (Known tradeoff speed for space.)</p>

<p>Intra frames are preferably used in most media players for so called <em>fast seek</em> (fast because of skipping the necessity of reading other frames and computing from them) - see for example </p>

<pre><code>View -&gt; Options -&gt; Tweaks -&gt; Fast seek (on keyframe)
</code></pre>

<p>in Media Player Classic (from <a href="https://www.codecguide.com/" rel="nofollow noreferrer">K-Lite Codec Pack</a>):</p>

<p><a href="https://i.sstatic.net/TgXAh.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/TgXAh.png" alt="enter image description here"></a></p>

<p>Adding more intra frames is important for relatively slow devices (e. g. smartphones) because after jump to non-intra frame <em>they played back ugly colored and broken video</em> while they meet the next intra frame - so for common density of 1 intra frame for 250 frames and the 25 fps the user may wait almost 10 second for restoring the image.</p>

CC BY-SA 4.0
2019-06-05T15:29:57.817Z
Good piece of info. Thanks.
angel_30
CC BY-SA 4.0
2019-06-05T14:53:51.503Z
2019-06-05T15:07:45.320Z
2019-06-05T15:07:45.320Z
MarianD
<p>I-frames are uncompressed frames and are what p and b frames reference to for compression. Yes I frames are higher quality. </p>

CC BY-SA 4.0
2018-09-12T04:39:41.187Z
I-frames aren't uncompressed - they simply rely on intra prediction.
Gyan
CC BY-SA 4.0
2018-09-12T16:24:27.107Z
Sorry, tried to answer that with out getting too technical. Yes I-frames are compressed to a degree, but to answer your question Tina they are higher is quality when compared to P and B frames.
user23155
CC BY-SA 4.0
2018-09-11T23:45:30.597Z
2018-09-11T23:45:30.597Z
user23155
<p>"I, B and P" don't refer to the viewed frames, they refer to the encoded, stored forms of the frames. However the frame is encoded in the file or stream, when it appears on the screen or is extracted as a still it is a complete frame, reconstructed from the IBP information as needed.</p>

CC BY-SA 4.0
2018-09-30T00:42:02.450Z
2018-09-30T00:42:02.450Z
Jim Mack
<p>I'm trying to capture various frames within a x264-encoded video files into <code>png</code> files (in <code>python</code>), and then compare the quality of them:</p>

<pre><code>cap = cv2.VideoCapture(filename);
//get frame_number for saving, and save the frame
cap.set(cv2.CAP_PROP_POS_FRAMES,frame_no);
ret, frame = cap.read()

cv2.imwrite(dir_path+'uniform_frame_'+str(frame_no)+".png", frame);
</code></pre>

<p>Now I was wondering if I fetch an <strong>I-Frame</strong>, does it mean that it has a higher quality than other frames, e.g. <strong>P-frames</strong> and <strong>B-Frames</strong>? (inherently, keyframes are not compressed, so they must have higher quality and less noise).</p>

CC BY-SA 4.0
2018-09-12T04:39:09.370Z
Please don't crosspost Qs.
Gyan
<video><video-quality><video-capture><keyframes><gop>
Frame capture from videos: I-frame vs P-frames
angel_30
# Frame capture from videos: I-frame vs P-frames

(Asked by: username_0 on 2018-09-11)

I'm trying to capture various frames within a x264-encoded video files into png files (in python), and then compare the quality of them:
cap = cv2.VideoCapture(filename);
//get frame_number for saving, and save the frame
cap.set(cv2.CAP_PROP_POS_FRAMES,frame_no);
ret, frame = cap.read()

cv2.imwrite(dir_path+'uniform_frame_'+str(frame_no)+".png", frame);

Now I was wondering if I fetch an I-Frame, does it mean that it has a higher quality than other frames, e.g. P-frames and B-Frames? (inherently, keyframes are not compressed, so they must have higher quality and less noise).

**Tags:** video, video-quality, video-capture, keyframes, gop

> **Comments:**
> **username_1**: Please don't crosspost Qs.  

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## 3 answers

### Answer by username_4 on 2018-09-30. Score: 3 | Accepted answer

"I, B and P" don't refer to the viewed frames, they refer to the encoded, stored forms of the frames. However the frame is encoded in the file or stream, when it appears on the screen or is extracted as a still it is a complete frame, reconstructed from the IBP information as needed.


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### Answer by username_2 on 2019-06-05. Score: 1

Intra frames (I-frames, keyframes) are independent of other frames - they contain the complete information for reconstructing the frame's image. There is no need for reading other frames and computing from them.
So it's about a speed, not about a quality. On the other hand, more intra frames, grater size of the file. (Known tradeoff speed for space.)
Intra frames are preferably used in most media players for so called fast seek (fast because of skipping the necessity of reading other frames and computing from them) - see for example 
View -> Options -> Tweaks -> Fast seek (on keyframe)

in Media Player Classic (from K-Lite Codec Pack):

Adding more intra frames is important for relatively slow devices (e. g. smartphones) because after jump to non-intra frame they played back ugly colored and broken video while they meet the next intra frame - so for common density of 1 intra frame for 250 frames and the 25 fps the user may wait almost 10 second for restoring the image.

> **Comments:**
> **username_0**: Good piece of info. Thanks.  

---

### Answer by username_3 on 2018-09-11. Score: -1

I-frames are uncompressed frames and are what p and b frames reference to for compression. Yes I frames are higher quality.

> **Comments:**
> **username_1**: I-frames aren't uncompressed - they simply rely on intra prediction.  
> **username_3**: Sorry, tried to answer that with out getting too technical. Yes I-frames are compressed to a degree, but to answer your question Tina they are higher is quality when compared to P and B frames.  

---

