How to choose the video version when I use youtube-dl to grab from BBC?

[dbigger]

~$ youtube-dl -F http://www.bbc.co.uk/iplayer/episode/xxxxxxxxxxxxxxxx

[info] Available formats :
format code                                                             extension  resolution note
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls-meta     mp4        multiple   Quality selection URL , h264@8490k
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls-meta  mp4        multiple   Quality selection URL , h264@8490k
iplayer_stb_streaming_sd_akamai_hls_open-meta                           mp4        multiple   Quality selection URL , h264@ 796k, 149.37MiB
iptv_streaming_1500_akamai_hls_open-meta                                mp4        multiple   Quality selection URL , h264@1500k, 279.46MiB
iplayer_stb_streaming_hd_akamai_hls_open-meta                           mp4        multiple   Quality selection URL , h264@2800k, 440.14MiB
iplayer_stb_streaming_sd_akamai_hls_open-797                            mp4        640x360     797k , h264@ 796k,  mp4a, 149.37MiB
iptv_streaming_1500_akamai_hls_open-797                                 mp4        832x468     797k , h264@1500k,  mp4a, 279.46MiB
iplayer_stb_streaming_hd_akamai_hls_open-797                            mp4        1280x720    797k , h264@2800k,  mp4a, 440.14MiB
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls-1012     mp4        1920x1080  1012k , h264@8490k, avc1 
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls-1012  mp4        1920x1080  1012k , h264@8490k, avc1 
iplayer_stb_streaming_sd_akamai_hls_open-1497                           mp4        640x360    1497k , h264@ 796k,  mp4a, 149.37MiB
iptv_streaming_1500_akamai_hls_open-1497                                mp4        832x468    1497k , h264@1500k,  mp4a, 279.46MiB
iplayer_stb_streaming_hd_akamai_hls_open-1497                           mp4        1280x720   1497k , h264@2800k,  mp4a, 440.14MiB
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls-1799     mp4        1920x1080  1799k , h264@8490k, avc1 
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls-1799  mp4        1920x1080  1799k , h264@8490k, avc1 
iplayer_stb_streaming_sd_akamai_hls_open-2361                           mp4        640x360    2361k , h264@ 796k,  mp4a, 149.37MiB
iptv_streaming_1500_akamai_hls_open-2361                                mp4        832x468    2361k , h264@1500k,  mp4a, 279.46MiB
iplayer_stb_streaming_hd_akamai_hls_open-2361                           mp4        1280x720   2361k , h264@2800k,  mp4a, 440.14MiB
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls-3116     mp4        1920x1080  3116k , h264@8490k, avc1 
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls-3116  mp4        1920x1080  3116k , h264@8490k, avc1 
stream-uk-iptv_streaming_concrete_combined_hd_mf_akamai_uk_hls-5509     mp4        1920x1080  5509k , h264@8490k, avc1 
stream-uk-iptv_streaming_concrete_combined_hd_mf_limelight_uk_hls-5509  mp4        1920x1080  5509k , h264@8490k, avc1  (best)

the format codes from bbc are different from youtube format codes. I want to download the 720p version. Can anyone help me? Thanks in advance.


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update: ok. after I checked the youtube-dl documentation, I have solved the problem by myself.