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4349 | Serge | 1 | @chapter Bitstream Filters |
2 | @c man begin BITSTREAM FILTERS |
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3 | |||
4 | When you configure your FFmpeg build, all the supported bitstream |
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5 | filters are enabled by default. You can list all available ones using |
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6 | the configure option @code{--list-bsfs}. |
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7 | |||
8 | You can disable all the bitstream filters using the configure option |
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9 | @code{--disable-bsfs}, and selectively enable any bitstream filter using |
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10 | the option @code{--enable-bsf=BSF}, or you can disable a particular |
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11 | bitstream filter using the option @code{--disable-bsf=BSF}. |
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12 | |||
13 | The option @code{-bsfs} of the ff* tools will display the list of |
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14 | all the supported bitstream filters included in your build. |
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15 | |||
16 | Below is a description of the currently available bitstream filters. |
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17 | |||
18 | @section aac_adtstoasc |
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19 | |||
20 | Convert MPEG-2/4 AAC ADTS to MPEG-4 Audio Specific Configuration |
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21 | bitstream filter. |
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22 | |||
23 | This filter creates an MPEG-4 AudioSpecificConfig from an MPEG-2/4 |
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24 | ADTS header and removes the ADTS header. |
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25 | |||
26 | This is required for example when copying an AAC stream from a raw |
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27 | ADTS AAC container to a FLV or a MOV/MP4 file. |
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28 | |||
29 | @section chomp |
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30 | |||
31 | Remove zero padding at the end of a packet. |
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32 | |||
33 | @section dump_extra |
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34 | |||
35 | Add extradata to the beginning of the filtered packets. |
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36 | |||
37 | The additional argument specifies which packets should be filtered. |
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38 | It accepts the values: |
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39 | @table @samp |
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40 | @item a |
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41 | add extradata to all key packets, but only if @var{local_header} is |
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42 | set in the @option{flags2} codec context field |
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43 | |||
44 | @item k |
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45 | add extradata to all key packets |
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46 | |||
47 | @item e |
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48 | add extradata to all packets |
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49 | @end table |
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50 | |||
51 | If not specified it is assumed @samp{k}. |
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52 | |||
53 | For example the following @command{ffmpeg} command forces a global |
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54 | header (thus disabling individual packet headers) in the H.264 packets |
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55 | generated by the @code{libx264} encoder, but corrects them by adding |
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56 | the header stored in extradata to the key packets: |
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57 | @example |
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58 | ffmpeg -i INPUT -map 0 -flags:v +global_header -c:v libx264 -bsf:v dump_extra out.ts |
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59 | @end example |
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60 | |||
61 | @section h264_mp4toannexb |
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62 | |||
63 | Convert an H.264 bitstream from length prefixed mode to start code |
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64 | prefixed mode (as defined in the Annex B of the ITU-T H.264 |
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65 | specification). |
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66 | |||
67 | This is required by some streaming formats, typically the MPEG-2 |
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68 | transport stream format ("mpegts"). |
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69 | |||
70 | For example to remux an MP4 file containing an H.264 stream to mpegts |
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71 | format with @command{ffmpeg}, you can use the command: |
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72 | |||
73 | @example |
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74 | ffmpeg -i INPUT.mp4 -codec copy -bsf:v h264_mp4toannexb OUTPUT.ts |
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75 | @end example |
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76 | |||
77 | @section imx_dump_header |
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78 | |||
79 | @section mjpeg2jpeg |
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80 | |||
81 | Convert MJPEG/AVI1 packets to full JPEG/JFIF packets. |
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82 | |||
83 | MJPEG is a video codec wherein each video frame is essentially a |
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84 | JPEG image. The individual frames can be extracted without loss, |
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85 | e.g. by |
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86 | |||
87 | @example |
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88 | ffmpeg -i ../some_mjpeg.avi -c:v copy frames_%d.jpg |
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89 | @end example |
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90 | |||
91 | Unfortunately, these chunks are incomplete JPEG images, because |
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92 | they lack the DHT segment required for decoding. Quoting from |
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93 | @url{http://www.digitalpreservation.gov/formats/fdd/fdd000063.shtml}: |
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94 | |||
95 | Avery Lee, writing in the rec.video.desktop newsgroup in 2001, |
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96 | commented that "MJPEG, or at least the MJPEG in AVIs having the |
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97 | MJPG fourcc, is restricted JPEG with a fixed -- and *omitted* -- |
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98 | Huffman table. The JPEG must be YCbCr colorspace, it must be 4:2:2, |
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99 | and it must use basic Huffman encoding, not arithmetic or |
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100 | progressive. . . . You can indeed extract the MJPEG frames and |
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101 | decode them with a regular JPEG decoder, but you have to prepend |
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102 | the DHT segment to them, or else the decoder won't have any idea |
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103 | how to decompress the data. The exact table necessary is given in |
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104 | the OpenDML spec." |
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105 | |||
106 | This bitstream filter patches the header of frames extracted from an MJPEG |
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107 | stream (carrying the AVI1 header ID and lacking a DHT segment) to |
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108 | produce fully qualified JPEG images. |
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109 | |||
110 | @example |
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111 | ffmpeg -i mjpeg-movie.avi -c:v copy -bsf:v mjpeg2jpeg frame_%d.jpg |
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112 | exiftran -i -9 frame*.jpg |
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113 | ffmpeg -i frame_%d.jpg -c:v copy rotated.avi |
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114 | @end example |
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115 | |||
116 | @section mjpega_dump_header |
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117 | |||
118 | @section movsub |
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119 | |||
120 | @section mp3_header_compress |
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121 | |||
122 | @section mp3_header_decompress |
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123 | |||
124 | @section noise |
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125 | |||
126 | @section remove_extra |
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127 | |||
128 | @c man end BITSTREAM FILTERS |