特殊视频构造总结

 

由于最近在测试画中画的功能，需要构造一批特殊的视频和图片进行异常场景的测试，现总结如下：

1.查看视频基本信息

首先将被测视频放在指定目录(/Users/ceshi/Downloads/a.mp4)，然后打开终端输入如下命令:

cd /Users/ceshi/Downloads/
mediainfo a.mp4
ffprobe -v quiet -print_format json -show_format -show_streams -show_error -show_chapters a.mp4

 

输出结果如下：

{
    "streams":[
        {
            "index":0,
            "codec_name":"h264",
            "codec_long_name":"H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
            "profile":"High",
            "codec_type":"video",
            "codec_tag_string":"avc1",
            "codec_tag":"0x31637661",
            "width":720,
            "height":1280,
            "coded_width":720,
            "coded_height":1280,
            "closed_captions":0,
            "film_grain":0,
            "has_b_frames":2,
            "sample_aspect_ratio":"1:1",
            "display_aspect_ratio":"9:16",
            "pix_fmt":"yuv420p",
            "level":32,
            "color_range":"tv",
            "color_space":"bt709",
            "color_transfer":"bt709",
            "color_primaries":"bt709",
            "chroma_location":"left",
            "field_order":"progressive",
            "refs":1,
            "is_avc":"true",
            "nal_length_size":"4",
            "id":"0x1",
            "r_frame_rate":"60/1",
            "avg_frame_rate":"3940/83",
            "time_base":"1/15360",
            "start_pts":0,
            "start_time":"0.000000",
            "duration_ts":318720,
            "duration":"20.750000",
            "bit_rate":"1790467",
            "bits_per_raw_sample":"8",
            "nb_frames":"985",
            "extradata_size":49,
            "disposition":{
                "default":1,
                "dub":0,
                "original":0,
                "comment":0,
                "lyrics":0,
                "karaoke":0,
                "forced":0,
                "hearing_impaired":0,
                "visual_impaired":0,
                "clean_effects":0,
                "attached_pic":0,
                "timed_thumbnails":0,
                "captions":0,
                "descriptions":0,
                "metadata":0,
                "dependent":0,
                "still_image":0
            },
            "tags":{
                "language":"und",
                "handler_name":"VideoHandler",
                "vendor_id":"[0][0][0][0]"
            }
        },
        {
            "index":1,
            "codec_name":"aac",
            "codec_long_name":"AAC (Advanced Audio Coding)",
            "profile":"LC",
            "codec_type":"audio",
            "codec_tag_string":"mp4a",
            "codec_tag":"0x6134706d",
            "sample_fmt":"fltp",
            "sample_rate":"44100",
            "channels":2,
            "channel_layout":"stereo",
            "bits_per_sample":0,
            "id":"0x2",
            "r_frame_rate":"0/0",
            "avg_frame_rate":"0/0",
            "time_base":"1/44100",
            "start_pts":0,
            "start_time":"0.000000",
            "duration_ts":917456,
            "duration":"20.803991",
            "bit_rate":"128009",
            "nb_frames":"898",
            "extradata_size":2,
            "disposition":{
                "default":1,
                "dub":0,
                "original":0,
                "comment":0,
                "lyrics":0,
                "karaoke":0,
                "forced":0,
                "hearing_impaired":0,
                "visual_impaired":0,
                "clean_effects":0,
                "attached_pic":0,
                "timed_thumbnails":0,
                "captions":0,
                "descriptions":0,
                "metadata":0,
                "dependent":0,
                "still_image":0
            },
            "tags":{
                "language":"und",
                "handler_name":"SoundHandler",
                "vendor_id":"[0][0][0][0]"
            }
        }
    ],
    "chapters":[

    ],
    "format":{
        "filename":"a.mp4",
        "nb_streams":2,
        "nb_programs":0,
        "format_name":"mov,mp4,m4a,3gp,3g2,mj2",
        "format_long_name":"QuickTime / MOV",
        "start_time":"0.000000",
        "duration":"20.851000",
        "size":"5010419",
        "bit_rate":"1922370",
        "probe_score":100,
        "tags":{
            "major_brand":"isom",
            "minor_version":"512",
            "compatible_brands":"isomiso2avc1mp41",
            "comment":"vid:v0200fg10000c8rfcnbc77u6dmhs6mo0",
            "encoder":"Lavf58.45.100"
        }
    }
}

 

2.查看视频I帧/B帧/P帧的分布及数量

查看视频总帧数

ffprobe -v error -count_frames -select_streams v:0 -show_entries stream=nb_read_frames -of default=nokey=1:noprint_wrappers=1 a.mp4

 

查看每个帧的分布

ffprobe -show_frames a.mp4 | grep pict_type
ffprobe -show_frames -i a.mp4 | grep "pict_type=" > a.txt

 

关于视频的I帧/B帧/P帧数量可以用如下Python脚本统计

# coding=utf-8
# 打开文件
f = open('/Users/ceshi/Downloads/a.txt', 'r', encoding='UTF-8')
# 读取文件所有行
content = f.readlines()
contentLines = ''

frame = ["I", "P", "B"]
rate = {}

# 依次迭代所有行
for line in content:
    # 去除空格
    line = line.strip()
    # 如果是空行则跳过
    if len(line) == 0:
        continue
    contentLines = contentLines + line
    for x in range(0, len(line)):
        if line[x] not in rate:
            rate[line[x]] = 0
        rate[line[x]] += 1

rate = sorted(rate.items(), key=lambda e: e[1], reverse=True)

for i in rate:
    if i[0] in frame:
        print(i[0], "帧的数量:", i[1])

f.close()

 

输出结果：

/Users/ceshi/PycharmProjects/pythonProject/venv/bin/python /Users/ceshi/PycharmProjects/PythonProject/count.py
 
B 帧的数量: 705
 
P 帧的数量: 274
 
I 帧的数量: 6
 
Process finished with exit code 0

查看key_frame分布

ffprobe -show_frames a.mp4 | grep key_frame

查看关键帧数量

ffprobe -v error -count_frames -select_streams v:0 -show_entries stream=nb_read_frames -of default=nokey=1:noprint_wrappers=1 -skip_frame nokey a.mp4

查看关键帧所在帧数

ffprobe -v error -select_streams v -show_frames -show_entries frame=pict_type -of csv a.mp4 | grep -n I | cut -d ':' -f 1 > d.txt

# coding=utf-8
newList = []
doneList = []
 
 
def diffList():
    f = open('/Users/ceshi/Downloads/d.txt', 'r', encoding='UTF-8')
    content = f.readlines()
    for line in content:
        line = line.strip()
        if len(line) == 0:
            continue
        newList.append(int(line))
    f.close()
    for i, j in zip(newList[0::], newList[1::]):
        doneList.append(j - i)
    print(doneList)
 
 
diffList()

输出结果：

/Users/ceshi/PycharmProjects/pythonProject/venv/bin/python /Users/ceshi/PycharmProjects/PythonProject/testnum.py
 
[242, 232, 75, 234, 113]
 
Process finished with exit code 0

3.修改视频的GOP大小和B帧数量

设置关键帧和B帧数量

ffmpeg -i a.mp4 -vcodec libx264 -bf 0 -g 1 -x264-params "keyint=250:min-keyint=50" -crf 26 -an -y a.mp4

-bf 0 : B帧数量

keyint ：关键帧的最大间隔，即GOP长度

min-keyint ：关键帧的最小间隔

说明：

帧率FPS=视频帧总数/视频时长

GOP设置的建议；[2*FPS,4*FPS]