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  • Libavcodec : How to tell end of access unit when decoding H.264 stream

    22 septembre 2011, par Flame

    I'm receiving H.264 video over RTP and decoding it with libavcodec. I'm unpackaging the NAL units from the RTP packets before feeding them to avcodec (including reassembling fragmentation units).

    I'm trying to show effective decoding frame rate. I used to log the time after a successful decode video call where *got_picture_ptr is non-zero. So far this worked since I only ever got video where there was one slice per frame. But now I receive video where both I and P frames consist of 2 NAL units each, of types 5 and 1 respectively. Now when I feed the either slice of a frame, decode_video return that it got a picture, and the pAVFrame->coded_picture_number is increased from every slice.

    How do I go about reliably finding the beginning or end of a video frame/picture/access unit?

    I've dumped out a few NAL units from the stream and run them through h264_analyze from h264bitstream.

    Output from h264_analyze on 4 NAL Units

    !! Found NAL at offset 695262 (0xA9BDE), size 25 (0x0019) 
==================== NAL ====================
 forbidden_zero_bit : 0 
 nal_ref_idc : 1 
 nal_unit_type : 7 ( Sequence parameter set ) 
======= SPS =======
 profile_idc : 66 
 constraint_set0_flag : 1 
 constraint_set1_flag : 1 
 constraint_set2_flag : 1 
 constraint_set3_flag : 0 
 reserved_zero_4bits : 0 
 level_idc : 32 
 seq_parameter_set_id : 0 
 chroma_format_idc : 0 
 residual_colour_transform_flag : 0 
 bit_depth_luma_minus8 : 0 
 bit_depth_chroma_minus8 : 0 
 qpprime_y_zero_transform_bypass_flag : 0 
 seq_scaling_matrix_present_flag : 0 
 log2_max_frame_num_minus4 : 12 
 pic_order_cnt_type : 2 
   log2_max_pic_order_cnt_lsb_minus4 : 0 
   delta_pic_order_always_zero_flag : 0 
   offset_for_non_ref_pic : 0 
   offset_for_top_to_bottom_field : 0 
   num_ref_frames_in_pic_order_cnt_cycle : 0 
 num_ref_frames : 1 
 gaps_in_frame_num_value_allowed_flag : 0 
 pic_width_in_mbs_minus1 : 79 
 pic_height_in_map_units_minus1 : 44 
 frame_mbs_only_flag : 1 
 mb_adaptive_frame_field_flag : 0 
 direct_8x8_inference_flag : 1 
 frame_cropping_flag : 0 
   frame_crop_left_offset : 0 
   frame_crop_right_offset : 0 
   frame_crop_top_offset : 0 
   frame_crop_bottom_offset : 0 
 vui_parameters_present_flag : 1 
=== VUI ===
 aspect_ratio_info_present_flag : 1 
   aspect_ratio_idc : 1 
     sar_width : 0 
     sar_height : 0 
 overscan_info_present_flag : 0 
   overscan_appropriate_flag : 0 
 video_signal_type_present_flag : 1 
   video_format : 5 
   video_full_range_flag : 1 
   colour_description_present_flag : 0 
     colour_primaries : 0 
   transfer_characteristics : 0 
   matrix_coefficients : 0 
 chroma_loc_info_present_flag : 0 
   chroma_sample_loc_type_top_field : 0 
   chroma_sample_loc_type_bottom_field : 0 
 timing_info_present_flag : 1 
   num_units_in_tick : 1 
   time_scale : 25 
   fixed_frame_rate_flag : 0 
 nal_hrd_parameters_present_flag : 0 
 vcl_hrd_parameters_present_flag : 0 
   low_delay_hrd_flag : 0 
 pic_struct_present_flag : 0 
 bitstream_restriction_flag : 1 
   motion_vectors_over_pic_boundaries_flag : 1 
   max_bytes_per_pic_denom : 0 
   max_bits_per_mb_denom : 0 
   log2_max_mv_length_horizontal : 6 
   log2_max_mv_length_vertical : 6 
   num_reorder_frames : 0 
   max_dec_frame_buffering : 1 
=== HRD ===
 cpb_cnt_minus1 : 0 
 bit_rate_scale : 0 
 cpb_size_scale : 0 
 initial_cpb_removal_delay_length_minus1 : 0 
 cpb_removal_delay_length_minus1 : 0 
 dpb_output_delay_length_minus1 : 0 
 time_offset_length : 0 
!! Found NAL at offset 695290 (0xA9BFA), size 4 (0x0004) 
==================== NAL ====================
 forbidden_zero_bit : 0 
 nal_ref_idc : 1 
 nal_unit_type : 8 ( Picture parameter set ) 
======= PPS =======
 pic_parameter_set_id : 0 
 seq_parameter_set_id : 0 
 entropy_coding_mode_flag : 0 
 pic_order_present_flag : 0 
 num_slice_groups_minus1 : 0 
 slice_group_map_type : 0 
 num_ref_idx_l0_active_minus1 : 0 
 num_ref_idx_l1_active_minus1 : 0 
 weighted_pred_flag : 0 
 weighted_bipred_idc : 0 
 pic_init_qp_minus26 : 3 
 pic_init_qs_minus26 : 0 
 chroma_qp_index_offset : 0 
 deblocking_filter_control_present_flag : 1 
 constrained_intra_pred_flag : 0 
 redundant_pic_cnt_present_flag : 0 
 transform_8x8_mode_flag : 1 
 pic_scaling_matrix_present_flag : 0 
 second_chroma_qp_index_offset : 1 
!! Found NAL at offset 695297 (0xA9C01), size 50725 (0xC625) 
==================== NAL ====================
 forbidden_zero_bit : 0 
 nal_ref_idc : 1 
 nal_unit_type : 5 ( Coded slice of an IDR picture ) 
======= Slice Header =======
 first_mb_in_slice : 0 
 slice_type : 2 ( I slice ) 
 pic_parameter_set_id : 0 
 frame_num : 0 
 field_pic_flag : 0 
 bottom_field_flag : 0 
 idr_pic_id : 0 
 pic_order_cnt_lsb : 0 
 delta_pic_order_cnt_bottom : 0 
 redundant_pic_cnt : 0 
 direct_spatial_mv_pred_flag : 0 
 num_ref_idx_active_override_flag : 0 
 num_ref_idx_l0_active_minus1 : 0 
 num_ref_idx_l1_active_minus1 : 0 
 cabac_init_idc : 0 
 slice_qp_delta : 5 
 sp_for_switch_flag : 0 
 slice_qs_delta : 0 
 disable_deblocking_filter_idc : 0 
 slice_alpha_c0_offset_div2 : 0 
 slice_beta_offset_div2 : 0 
 slice_group_change_cycle : 0 
=== Prediction Weight Table ===
 luma_log2_weight_denom : 0 
 chroma_log2_weight_denom : 0 
 luma_weight_l0_flag : 0 
 chroma_weight_l0_flag : 0 
 luma_weight_l1_flag : 0 
 chroma_weight_l1_flag : 0 
=== Ref Pic List Reordering ===
 ref_pic_list_reordering_flag_l0 : 0 
 ref_pic_list_reordering_flag_l1 : 0 
=== Decoded Ref Pic Marking ===
 no_output_of_prior_pics_flag : 0 
 long_term_reference_flag : 0 
 adaptive_ref_pic_marking_mode_flag : 0 
!! Found NAL at offset 746025 (0xB6229), size 38612 (0x96D4) 
==================== NAL ====================
 forbidden_zero_bit : 0 
 nal_ref_idc : 1 
 nal_unit_type : 5 ( Coded slice of an IDR picture ) 
======= Slice Header =======
 first_mb_in_slice : 1840 
 slice_type : 2 ( I slice ) 
 pic_parameter_set_id : 0 
 frame_num : 0 
 field_pic_flag : 0 
 bottom_field_flag : 0 
 idr_pic_id : 0 
 pic_order_cnt_lsb : 0 
 delta_pic_order_cnt_bottom : 0 
 redundant_pic_cnt : 0 
 direct_spatial_mv_pred_flag : 0 
 num_ref_idx_active_override_flag : 0 
 num_ref_idx_l0_active_minus1 : 0 
 num_ref_idx_l1_active_minus1 : 0 
 cabac_init_idc : 0 
 slice_qp_delta : 5 
 sp_for_switch_flag : 0 
 slice_qs_delta : 0 
 disable_deblocking_filter_idc : 0 
 slice_alpha_c0_offset_div2 : 0 
 slice_beta_offset_div2 : 0 
 slice_group_change_cycle : 0 
=== Prediction Weight Table ===
 luma_log2_weight_denom : 0 
 chroma_log2_weight_denom : 0 
 luma_weight_l0_flag : 0 
 chroma_weight_l0_flag : 0 
 luma_weight_l1_flag : 0 
 chroma_weight_l1_flag : 0 
=== Ref Pic List Reordering ===
 ref_pic_list_reordering_flag_l0 : 0 
 ref_pic_list_reordering_flag_l1 : 0 
=== Decoded Ref Pic Marking ===
 no_output_of_prior_pics_flag : 0 
 long_term_reference_flag : 0 
 adaptive_ref_pic_marking_mode_flag : 0

    Both I slices show the frame_num = 0. The next 2 (not shown) have frame_num = 1.

  • ffmpeg reencoding of flv files from MAC

    22 septembre 2011, par Nick Mitin

    I've recorded a video from a webcam on mac and now i'm trying to reencode it, but ffmpeg does not recognize audio stream:

    FFmpeg version git-120610e, Copyright (c) 2000-2010 the FFmpeg developers
  built on Sep 21 2010 15:56:57 with gcc 4.4.1
  configuration: --enable-gpl --enable-version3 --enable-nonfree --enable-postproc --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libmp3lame --enable-libx264
  libavutil     50.27. 0 / 50.27. 0
  libavcore      0. 9. 0 /  0. 9. 0
  libavcodec    52.89. 0 / 52.89. 0
  libavformat   52.78. 5 / 52.78. 5
  libavdevice   52. 2. 2 / 52. 2. 2
  libavfilter    1.39. 0 /  1.39. 0
  libswscale     0.11. 0 /  0.11. 0
  libpostproc   51. 2. 0 / 51. 2. 0
[flv @ 0x1e79470] Estimating duration from bitrate, this may be inaccurate
Input #0, flv, from '10125174c09241f6536ccbe503ebbc00.flv':
  Duration: 00:00:22.68, start: 0.000000, bitrate: N/A
    Stream #0.0: Video: flv, yuv420p, 640x480, 1k tbr, 1k tbn, 1k tbc
    Stream #0.1: Audio: [0][0][0][0] / 0x0000, 0 channels

    Is it possible to make ffmpeg to support audio stream form flv recorded on MAC?

  • How to capture camera devices on Windows using Libav ?

    22 septembre 2011, par Occulta

    Is there any way to capture frames from as many camera types as DirectShow do on Windows platform using Libav? I need to capture a camera output without using DirectShow filters and I want my application to work with many camera devices types.

    I have searched the Internet about this capability of libav and found that it can be done via libav using special input format "vfwcap". Something like that (don't sure about code correctness - I wrote it by myself):

    AVFormatParameters formatParams = NULL;
AVInputFormat* pInfmt = NULL;
pInFormatCtx*  pInFormatCtx = NULL;

av_register_all();

//formatParams.device = NULL; //this was probably deprecated and then removed
formatParams.channel = 0;
formatParams.standard = "ntsc"; //deprecated too but still available
formatParams.width = 640;
formatParams.height = 480;
formatParams.time_base.num = 1000;
formatParams.time_base.den = 30000; //so we want 30000/1000 = 30 frames per second
formatParams.prealloced_context = 0;


pInfmt = av_find_input_format("vfwcap");
if( !pInfmt )
{
  fprintf(stderr,"Unknown input format\n");
  return -1;
}

// Open video file (formatParams can be NULL for autodetecting probably)
if (av_open_input_file(&pInFormatCtx, 0, pInfmt, 0, formatParams) < 0)
   return -1; // Couldn't open device

/* Same as video4linux code*/

    So another question is: how many devices are supported by Libav? All I have found about capture cameras output with libav on windows is advice to use DirectShow for this purpose because libav supports too few devices. Maybe situation has already changed now and it does support enough devices to use it in production applications?

    If this isn't possible.. Well I hope my question won't be useless and this composed from different sources piece of code will help someone interested in this theme 'coz there are really too few information about it in the whole internet.

  • FFMPeg Windows C# H264

    21 septembre 2011, par Allen Ho

    I am trying to use SharpFFMpeg

    http://sourceforge.net/projects/sharpffmpeg/

    I found avcodec-52.dll and avformat-52.dll somewhere on the Net...

    When I use SharpFFMpeg and make calls like av_init_packet

    I get PInvoke errors like so

    PInvokeStackImbalance was detected Message: A call to PInvoke function 'WpfApplicationFFMpegTest!FFmpegSharp.Interop.FFmpeg::av_init_packet' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature.

    In a nutshell I am trying to decode H264 and display the incoming stream from a camera...

    Just wondering if anyone has been able to do this succesfully in C#?

    Thanks

  • How to get correct video dimensions

    21 septembre 2011, par David542

    I've been using ffmpeg -i and mediainfo (CLI) to get the dimensions of a video. Unfortunately, neither have been very good at returning the correct dimensions. This is especially true if the video has been modified since its initial export.

    What is the best way to get the correct dimensions of a video file?

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