Read directly from 'senc' box when 'senc' box is present

media/test/data/README

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 bear-320x240.webm - WebM encode of bear.1280x720.mp4 resized to 320x240.
 bear-320x240-video-only.webm - The video track of bear-320x240.webm.
 bear-320x240-audio-only.webm - The audio track of bear-320x240.webm.
 bear-vp9.webm - VP9 video only WebM file.
 bear-vp9-opus.webm - VP9 Video with Opus Audio.
 bear-vp8-webvtt.webm - WebM VP8 video with WebVTT subtitle track.
@@ skipping 59 matching lines @@
 bear-320x240-av_enc-a.webm - bear-320x240.webm with audio track encrypted using key ID [1] and key [2].
 bear-320x240-v_enc-v.webm - bear-320x240-video-only.webm encrypted using key ID [1] and key [2].
 bear-320x240-v-vp9_enc-v.webm - bear-vp9.webm VP9 video only encrypted using key ID [1] and key [2].
 bear-320x240-opus-a_enc-a.webm - bear-opus.webm encrypted using key ID [1] and key[2].
 bear-320x240-opus-av_enc-av.webm - bear-vp9-opus.webm with audio & video encrypted using key ID [1] and key[2].
 bear-320x240-opus-av_enc-v.webm - bear-vp9-opus.webm with video track encrypted using key ID [1] and key[2].
 bear-640x360-a_frag-cenc.mp4 - A fragmented MP4 version of the audio track of bear-640x360.mp4 encrypted (ISO CENC) using key ID [1] and key [2].
 bear-640x360-a_frag-cenc-key_rotation.mp4 - A fragmented MP4 version of the audio track of bear-640x360.mp4 encrypted (ISO CENC) using key ID [1] and key [2] with key rotation [3].
 bear-640x360-v_frag-cenc.mp4 - A fragmented MP4 version of the video track of bear-640x360.mp4 encrypted (ISO CENC) using key ID [1] and key [2]  and with sample encryption auxiliary information in the beginning of mdat box.
 bear-640x360-v_frag-cenc-senc.mp4 - Same as above, but with sample encryption information stored in SampleEncryption ('senc') box.
+bear-640x360-v_frag-cenc-senc-no-saiz-saio.mp4 - Same as above, but without saiz and saio boxes.
 bear-640x360-v_frag-cenc-key_rotation.mp4 - A fragmented MP4 version of the video track of bear-640x360.mp4 encrypted (ISO CENC) using key ID [1] and key [2] with key rotation [3].
 bear-a_enc-a.webm - bear-320x240-audio-only.webm encrypted using key ID [1] and key [2].
 frame_size_change-av_enc-v.webm - third_party/WebKit/LayoutTests/media/resources/frame_size_change.webm encrypted using key ID [1] and key [2].
 
 
 [1] 30313233343536373839303132333435
 [2] ebdd62f16814d27b68ef122afce4ae3c
 [3] KeyIds and Keys are created by left rotating key ID [1] and key [2] using
     std::rotate for every new crypto period. This is only for testing. The
     actual key rotation algorithm is often much more complicated.
@@ skipping 151 matching lines @@
 media/test/data/bbb-320x240-2video-2audio.mp4
   Generated using following commands
   // Download the source file with 1 video and 1 audio stream.
   wget http://distribution.bbb3d.renderfarming.net/video/mp4/bbb_sunflower_1080p_30fps_normal.mp4
   // Generate a scaled down to 320x240 video + 2 channel AAC LC audio from the source file.
   ffmpeg -i bbb_sunflower_1080p_30fps_normal.mp4 -c:v libx264 -crf 36 -vf  scale=320:240 -c:a libfdk_aac -ac 2 -t 24 bbb1.mp4
   // Generate a file with the original video scaled down to 320x240 and flipped upside down and sine wave instead of audio.
   ffmpeg -i bbb_sunflower_1080p_30fps_normal.mp4 -f lavfi -i "sine=frequency=500:sample_rate=48000" -map 0:v -map 1:a -c:v libx264 -crf 36 -vf scale=320:240,vflip -c:a libfdk_aac -ac 2 -t 24 bbb2.mp4
   // Combine the two files generated above into a single fragmented .mp4 file with 2 video and 2 audio tracks.
   ffmpeg -i bbb1.mp4 -i bbb2.mp4 -map 0:0 -map 0:1 -map 1:0 -map 1:1 -c:v copy -c:a copy -movflags frag_keyframe+omit_tfhd_offset+separate_moof bbb-320x240-2video-2audio.mp4